{"id":6981,"date":"2013-02-08T10:15:39","date_gmt":"2013-02-08T15:15:39","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=6981"},"modified":"2026-04-17T20:53:42","modified_gmt":"2026-04-18T01:53:42","slug":"markovnikovs-rule-1","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2013\/02\/08\/markovnikovs-rule-1\/","title":{"rendered":"Hydrohalogenation of Alkenes and Markovnikov&#8217;s Rule"},"content":{"rendered":"<p><strong>Hydrohalogenation of Alkenes and Markovnikov&#8217;s Rule<\/strong><\/p>\n<ul>\n<li>When hydrohalic acids (HCl, HBr, HI) are added to alkenes, <strong>addition reactions<\/strong> can occur, resulting in formation of a C-H and C-halogen bond and breakage of a C-C pi bond.<\/li>\n<li>The reaction tends to occur such that the halogen ends up attached to the carbon of the alkene attached to the fewest hydrogen atoms, a phenomenon known as <strong>Markovnikov&#8217;s Rule.\u00a0<\/strong><\/li>\n<li>Addition of H-X to alkenes occurs through a protonation of the alkene to give a carbocation intermediate, followed by addition of the halide to the carbocation.<\/li>\n<li>A better reformulation of Markovnikov&#8217;s rule is therefore that addition of HX to alkenes will proceed<strong>\u00a0through the most stable carbocation<\/strong>, which is generally the more substituted carbon of the alkene.<\/li>\n<li><span style=\"color: #800080;\"><em>(Note that H-Br with peroxides (RO-OR) operates through a different reaction mechanism &#8211; see <span style=\"color: #800080;\"><a style=\"color: #800080;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/04\/12\/addition-hbr-alkenes-roor-peroxides-free-radical\/\">Free Radical Addition of H-Br to Alkenes<\/a><\/span>).\u00a0<\/em><\/span><\/li>\n<li>Carbocation rearrangements (hydride or alkyl shifts) can occur if they will result in a more stable carbocation intermediate.<\/li>\n<li>H-X will also add to alkynes (<span style=\"color: #800080;\"><em>See: <span style=\"color: #800080;\"><a style=\"color: #800080;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/05\/24\/alkyne-reaction-patterns-the-carbocation-pathway\/\">Addition of HX to alkynes<\/a><\/span><\/em><\/span>) and dienes (<span style=\"color: #800080;\"><em>See: <span style=\"color: #800080;\"><a style=\"color: #800080;\" href=\"https:\/\/www.masterorganicchemistry.com\/2017\/03\/22\/reactions-of-dienes-12-and-14-addition\/\">1,2- and 1,4- Addition of HX To Dienes<\/a><\/span><\/em><\/span>) but will not add to aromatic rings.<\/li>\n<\/ul>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-35582\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/0-summary-of-addition-of-HX-to-alkenes-hydrohalogenation.gif\" alt=\"summary of addition of HX to alkenes hydrohalogenation\" width=\"640\" height=\"682\" \/><\/a><\/p>\n<p><strong>Table of Contents<\/strong><\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li><a href=\"#one\">Reaction of Alkenes With Hydrohalic Acids (HCl, HBr, HI)<\/a><\/li>\n<li><a href=\"#two\">Markovnikov&#8217;s Rule: The Halide Adds To The Most Substituted Carbon<\/a><\/li>\n<li><a href=\"#three\">Stereoselectivity (or Lack Thereof) In Alkene Hydrohalogenation<\/a><\/li>\n<li><a href=\"#four\">Hydrohalogenation of Alkenes: The Mechanism<\/a><\/li>\n<li><a href=\"#five\">The Reaction Energy Diagram<\/a><\/li>\n<li><a href=\"#six\">Carbocation Rearrangements &#8211; Hydride and Alkyl Shifts<\/a><\/li>\n<li><a href=\"#seven\">Alkynes, Dienes, Aromatic Rings, and the Cationic Cyclization of Alkenes<\/a><\/li>\n<li><a href=\"#eight\">Summary: Alkene Hydrohalogenation<\/a><\/li>\n<li><a href=\"#notes\">Notes<\/a><\/li>\n<li><a href=\"#quiz\">Quiz Yourself!<\/a><\/li>\n<li><a href=\"#references\">(Advanced) References and Further Reading<\/a><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<hr \/>\n<h2><a id=\"one\"><\/a>1. Reaction of Alkenes With Hydrohalic Acids (HCl, HBr, HI)<\/h2>\n<p>When alkenes are treated with <strong>hydrohalic acids<\/strong> (HCl, HBr, or HI) they form\u00a0<strong>alkyl halides.\u00a0<\/strong><\/p>\n<p>This is sometimes called\u00a0<strong>hydrohalogenation\u00a0<\/strong>of alkenes since it results in the addition of\u00a0<strong>hydrogen\u00a0<\/strong>and a\u00a0<strong>halogen.\u00a0<\/strong><\/p>\n<p>In these\u00a0<strong>addition reactions:\u00a0<\/strong><\/p>\n<ul>\n<li>the C-C pi bond and the H-X bond breaks;<\/li>\n<li>a new C-H and C-X bond forms (where X is Cl, Br, or I).<\/li>\n<\/ul>\n<p><img decoding=\"async\" class=\"alignnone wp-image-35574\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/1-hydrohalogenation-of-alkenes-through-addition-of-HX-to-alkenes-giving-alkyl-halides-gives-Markovnikov-products.gif\" alt=\"hydrohalogenation of alkenes through addition of HX to alkenes giving alkyl halides - gives Markovnikov products\" width=\"640\" height=\"295\" \/><\/a><\/p>\n<p>If we add up the bond dissociation energies (BDE&#8217;s) of the bonds that <strong>form<\/strong> (C-H, about 98 kcal\/mol, and C-Cl, about 81 kcal\/mol) and subtract their sum from those of the bonds that <strong>break<\/strong> (C-C pi, about 60 kcal\/mol, and H-Cl, about 103 kcal\/mol) the reaction is <strong>exothermic by about 18 kcal\/mol<\/strong> for the addition of HCl. [<span style=\"color: #993366;\"><em><a style=\"color: #993366;\" href=\"https:\/\/www2.chemistry.msu.edu\/faculty\/reusch\/OrgPage\/bndenrgy.htm\">Link to a useful table<\/a><\/em><\/span>]<\/p>\n<p><b>Acid<\/b> is required for these reactions to occur; no addition of halide to alkenes will happen in the absence of strong acid. (<span style=\"color: #993366;\"><em>In other words, HCl =\u00a0 \u2705, but NaCl = \u274c<\/em><\/span>).<\/p>\n<p>The new C-halogen bond tends to form on the <strong>most substituted<\/strong> carbon of the alkene (i.e. the one with the fewest carbons), and the new C-H bond tends to form on the carbon of the alkene containing the most hydrogens.<\/p>\n<h2><a id=\"two\"><\/a>2. Markovnikov&#8217;s Rule: Regioselectivity of HX Addition to Alkenes<\/h2>\n<p>The reactions of alkenes with\u00a0 has been known for over 150 years.<\/p>\n<p>When an alkene is not symmetrical, the reaction has the potential to form two different constitutional isomers (<span style=\"color: #993366;\"><em>&#8220;regioisomers&#8221;<\/em><\/span>). However, in many cases, one constitutional isomer is formed in a much higher proportion than the other. In other words, the reaction is <strong>regioselective<\/strong>.<\/p>\n<p>In an early study of this reaction, Russian chemist Victor Markovnikov published the observation that the <strong>halogen<\/strong> tended to add to the carbon of the alkene which was bonded to the <strong>least number<\/strong> of hydrogens.<\/p>\n<p>This has come to be known as &#8220;<strong>Markovnikov&#8217;s Rule<\/strong>&#8220;.<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-35575\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/2-Markovnikovs-rule-addition-of-halogen-to-most-substituted-carbon-examples-with-HI-and-HCl-.gif\" alt=\"Markovnikovs rule - addition of halogen to most substituted carbon - examples with HI and HCl\" width=\"640\" height=\"402\" \/><\/a><\/p>\n<p>Markovnikov&#8217;s rule is what we would call an &#8220;empirical&#8221; rule. It was based purely on observed results, without any real underlying understanding of the mechanism of the reaction.<\/p>\n<p><span style=\"color: #993366;\"><em>In later years people had a hard time replicating Markovnikov&#8217;s results with HBr, often finding that the least substituted regioisomer was formed instead!\u00a0 Later on, in the 1930s the cause of this aberrant regioselectivity was found to be the presence of <strong>peroxides<\/strong> in solvent, which led to a free-radical process for addition of H-Br to alkenes, which does not occur with H-I or H-Cl. See article &#8211; <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/04\/12\/addition-hbr-alkenes-roor-peroxides-free-radical\/\">Free-Radical addition of H-Br to Alkenes<\/a>. [<a href=\"#noteone\">Note 1<\/a>]<\/em><\/span><\/p>\n<p>Subsequently we tend to say, for better or worse, that addition reactions to alkenes that follow this pattern (<a href=\"https:\/\/www.masterorganicchemistry.com\/2023\/09\/15\/hydration-alkenes-acid\/\"><span style=\"color: #993366;\"><em>such as their reaction with H<sub>3<\/sub>O<sup>+<\/sup> <\/em><\/span><\/a>) are &#8220;<strong>Markovnikov-selective<\/strong>&#8220;, whereas reactions that follow the opposite pattern are &#8220;<strong>anti-Markovnikov selective<\/strong>&#8221; (<span style=\"color: #993366;\"><em>such as <span style=\"color: #993366;\"><a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/03\/28\/hydroboration-of-alkenes-the-mechanism\/\">hydroboration of alkenes<\/a><\/span><\/em><\/span>).<\/p>\n<p>See if you can apply the pattern in the reaction of the alkene below (1-methylcyclopentene) with H-Cl.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35565\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35565\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35565\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35565\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35565\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35565 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35565\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-t45qs\" data-id=\"t45qs\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2588-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2588-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>Another example is below. Draw the major product(s) and determine how they will be related:<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35566\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35566\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35566\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35566\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35566\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35566 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35566\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-zyp61\" data-id=\"zyp61\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2589-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2589-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>Can you work backwards to come up with the best starting material for this reaction?<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35567\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35567\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35567\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35567\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35567\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35567 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35567\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-qc9g4\" data-id=\"qc9g4\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2590-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2590-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<h2><a id=\"three\"><\/a>3. Stereoselectivity (Or Lack Thereof) In Addition of HX To Alkenes<\/h2>\n<p>When addition reactions occur across an alkene pi-bond, the (sp<sup>2<\/sup>-hybridized) trigonal planar carbons of the alkene are converted into (sp<sup>3<\/sup>-hybridized) tetrahedral carbons, and with this comes the potential for formation of stereoisomers. (<span style=\"color: #993366;\"><em>See article: <span style=\"color: #993366;\"><a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2018\/09\/10\/types-of-isomers\/\">Types of Isomers<\/a><\/span><\/em><\/span>)<\/p>\n<ul>\n<li>When the two new bonds to carbon are formed on the same face of the alkene, the addition is said to be &#8220;<strong><em>syn<\/em><\/strong>&#8220;<\/li>\n<li>When the two new bonds are formed on opposite faces of the alkene, the addition is said to be &#8220;<strong><em>anti<\/em><\/strong>&#8220;.<\/li>\n<\/ul>\n<p>Addition reactions that give primarily\u00a0<em>syn<\/em> or\u00a0<em>anti<\/em> products are said to be\u00a0<strong>stereoselective<\/strong>, and we will meet many examples in subsequent articles in this chapter (<span style=\"color: #993366;\"><em>e.g. <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/03\/15\/alkene-bromination-mechanism\/\">halogenation<\/a> is stereoselective for anti products, and <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/03\/28\/hydroboration-of-alkenes-the-mechanism\/\">hydroboration<\/a> is stereoselective for syn products<\/em><\/span>).<\/p>\n<p>Addition of H-X to alkenes gives a mixture of\u00a0<em>syn<\/em> addition products <strong>and<\/strong>\u00a0<em>anti<\/em> addition products [<span style=\"color: #ff0000;\"><a href=\"#notetwo\">Note 2<\/a><\/span>].<\/p>\n<p>In other words, the reaction is <strong>not<\/strong> particularly stereoselective.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35576\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/6-addition-of-HCl-to-dimethylcyclopentene-gives-a-mixture-of-syn-and-anti-addition-addition-of-hcl-not-stereoselective.gif\" alt=\"addition of HCl to dimethylcyclopentene gives a mixture of syn and anti addition - addition of hcl not stereoselective\" width=\"640\" height=\"312\" \/><\/a><\/p>\n<p>This lack of stereoselectivity leads to mixtures of\u00a0<em>syn<\/em> and\u00a0<em>anti<\/em> addition products, in some cases each as mixtures of enantiomers. See if you can draw the products of the reaction below:<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35568\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35568\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35568\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35568\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35568\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35568 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35568\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-wixyr\" data-id=\"wixyr\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2591-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2591-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<h2><a id=\"four\"><\/a>4. Hydrohalogenation of Alkenes: The Mechanism<\/h2>\n<p>Markovnikov was one of the more prominent chemists of his era, but back in 1870 he didn&#8217;t know <strong>why<\/strong> the reaction tended to give the more substituted product.\u00a0 <em><span style=\"color: #993366;\">The first to really figure it out was Lucas in 1924 [Ref], based on observations that alkyl groups are more &#8220;electron releasing&#8221;.\u00a0<\/span><\/em><\/p>\n<p>After many decades it was finally proposed that reaction goes through an intermediate <strong>carbocation<\/strong>. (<span style=\"color: #993366;\"><em>The existence of carbocations was a fairly controversial subject until the 1930&#8217;s<\/em><\/span>).<\/p>\n<p>In the first step, the alkene (a nucleophile) is protonated by strong acid, resulting in a new carbocation. [<a href=\"#notethree\"><span style=\"color: #ff0000;\">Note 3<\/span><\/a> ]<\/p>\n<p>Depending on where protonation occurs, two different carbocations may be formed. Being electron-poor species, carbocations are stabilized by adjacent electron-donating groups as well as by delocalization through resonance. (<span style=\"color: #800080;\"><em>See article &#8211; <a style=\"color: #800080;\" href=\"https:\/\/www.masterorganicchemistry.com\/2011\/03\/11\/3-factors-that-stabilize-carbocations\/\">3 Factors Which Stabilize Carbocations<\/a><\/em><\/span>).<\/p>\n<p>The transition state leading to the\u00a0<strong>most stable\u00a0carbocation<\/strong> will be lower in energy, which tends to be the\u00a0<strong>most substituted\u00a0<\/strong>carbocation.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35577\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/9-mechanism-of-hydrohalogenation-of-alkenes-first-step-is-protonation-of-alkene-to-give-carbocation.gif\" alt=\"mechanism of hydrohalogenation of alkenes - first step is protonation of alkene to give carbocation\" width=\"640\" height=\"376\" \/><\/a><\/p>\n<p><span style=\"color: #800080;\"><em>The arrow pushing for alkenes reacting with acids like H-X can be a little ambiguous &#8211; see <span style=\"color: #ff0000;\"><a href=\"#notefour\">Note 4<\/a><\/span>.\u00a0<\/em><\/span><\/p>\n<p>So it is ultimately this carbocation intermediate which is the underlying reason for why Markovnikov&#8217;s rule is observed.<\/p>\n<p>Carbocations have an empty p-orbital and readily accept a pair of electrons from whatever Lewis bases happen to be present in solution.<\/p>\n<p>In the second step, the best nucleophile present (which tends to be the halide ion) then attacks the carbocation, forming the alkyl halide.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35578\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/10-mechanism-for-addition-of-halide-ion-to-carbocation-to-give-alkyl-halide.gif\" alt=\"mechanism for addition of halide ion to carbocation to give alkyl halide\" width=\"640\" height=\"309\" \/><\/a><\/p>\n<p><span style=\"color: #800080;\"><em>To reiterate: Markovnikov went to his grave not knowing this mechanism. Heck, many chemists of his time didn&#8217;t even accept that carbon was tetrahedral!\u00a0 So if you didn&#8217;t figure this mechanism out immediately, that&#8217;s to be expected and certainly nothing to feel bad about.\u00a0 The body of knowledge that is chemistry is built up of thousands of little experiments that eventually grew into the framework we have today.\u00a0<\/em><\/span><\/p>\n<h2><a id=\"five\"><\/a>5. Reaction Energy Diagram For Alkene Hydrohalogenation<\/h2>\n<p>Sometimes it can be helpful to trace out the energy profile of a reaction as it progresses from starting material to products.<\/p>\n<p>In these diagrams,\u00a0<strong>peaks\u00a0<\/strong>(local maxima) are\u00a0<strong>transition states<\/strong> and\u00a0<strong>valleys\u00a0<\/strong>(local minima) are\u00a0<strong>intermediates.\u00a0<\/strong><\/p>\n<p>A simple hydrohalogenation reaction has two steps &#8211; each of which has a transition state &#8211; and a single carbocation intermediate.<\/p>\n<ul>\n<li>In the first step, our intrepid alkene is protonated by strong acid, resulting in the high-energy\u00a0<strong>transition state\u00a0<\/strong>TS 1. This step has the highest <strong>activation energy <\/strong>(the barrier between reactants and transition state) making it the <strong>rate-determining step<\/strong> for this reaction.<\/li>\n<li>From the transition state (TS1) energy maximum, the reaction proceeds to the carbocation intermediate.<\/li>\n<li>The second step involves attack of the halide nucleophile on the carbocation, which proceeds through transition state 2 (TS2). Note that the activation energy for this step is considerably less than for protonation of the alkene &#8211; in other words, it will be the fast step.<\/li>\n<li>The reaction then proceeds through TS2 to give the final product, the alkyl halide.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35579\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/11-reaction-energy-diagram-for-addition-of-HX-to-alkenes-hydrohalogenation-transition-state.gif\" alt=\"reaction energy diagram for addition of HX to alkenes hydrohalogenation transition state\" width=\"640\" height=\"591\" \/><\/a><\/p>\n<h2><a id=\"six\"><\/a>6. Carbocation Rearrangements &#8211; Hydride and Alkyl Shifts<\/h2>\n<p>One key to the proposal of a carbocation intermediate was the observation that some hydrohalogenation reactions give products of\u00a0<strong>carbocation rearrangements\u00a0<\/strong>in addition to the expected addition product.<\/p>\n<p>For example when 4-methyl-1-butene was treated with HCl and allowed to sit at room temperature for an extended period, the product mixture was found to contain about half the expected Markovnikov addition product in addition to a new\u00a0<strong>tertiary\u00a0<\/strong>alkyl halide. [<a href=\"#reffour\">Ref<\/a>]<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35580\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/12-carbocation-rearrangement-reactions-occur-during-addition-of-HX-to-alkenes-hydride-shift.gif\" alt=\"carbocation rearrangement reactions occur during addition of HX to alkenes - hydride shift\" width=\"640\" height=\"270\" \/><\/a><\/p>\n<p>In this reaction the C-H bond that was originally part of the isopropyl group\u00a0<strong>migrates<\/strong> to the secondary alkyl carbon. (<span style=\"color: #800080;\"><em>See article &#8211; <span style=\"color: #800080;\"><a style=\"color: #800080;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/02\/26\/rearrangements-in-alkene-addition-reactions\/\">Rearrangements in Alkene Addition Reactions<\/a><\/span><\/em><\/span>)<\/p>\n<p>See if you can draw a reasonable mechanism!<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35569\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35569\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35569\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35569\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35569\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35569 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35569\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-nsf4y\" data-id=\"nsf4y\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2592-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2592-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>These rearrangements can occur when a more stable carbocation can result from migration of a hydride or alkyl group. When a quaternary carbon is adjacent to a secondary carbocation, alkyl groups can migrate.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35570\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35570\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35570\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35570\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35570\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35570 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35570\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-j4zvw\" data-id=\"j4zvw\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2593-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2593-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>Occasionally migrations between equivalently substituted groups can be favored, as in the example below.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35571\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35571\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35571\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35571\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35571\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35571 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35571\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-5igip\" data-id=\"5igip\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2594-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2594-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<h2><a id=\"seven\"><\/a>7. Other Applications of Hydrohalogenation<\/h2>\n<ul>\n<li>Alkynes will react with HX to give vinyl halides. A second equivalent of HX will give geminal dihalides. (<span style=\"color: #993366;\"><em>For more, see <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/05\/24\/alkyne-reaction-patterns-the-carbocation-pathway\/\">Alkyne Hydrohalogenation<\/a><\/em><\/span>)<\/li>\n<li>Dienes such as 1,3-butadiene will react with HX to give various products. See this article in the chapter on conjugated systems for more. (<span style=\"color: #993366;\"><em>See article: <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2017\/03\/22\/reactions-of-dienes-12-and-14-addition\/\">1,2- and 1,4-Addition of HX To Dienes<\/a><\/em><\/span>)<\/li>\n<li>Aromatic rings such as benzene will\u00a0<strong>not\u00a0<\/strong>undergo addition reactions with HX. Aromatic rings tend to react through substitution. More in the chapter on aromatic rings. (<span style=\"color: #993366;\"><em>See article: <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2017\/01\/20\/introduction-aromaticity\/\">Introduction to Aromaticity<\/a><\/em><\/span>)<\/li>\n<\/ul>\n<p>Carbocations are reactive intermediates and will readily combine with even poor Lewis bases.<\/p>\n<p>Sometimes those Lewis bases include\u00a0<strong>other alkenes\u00a0<\/strong>on the same molecule. This can result in cyclic molecules.<\/p>\n<p>For example, consider the reaction below:<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35572\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35572\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35572\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35572\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35572\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35572 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35572\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-lwclg\" data-id=\"lwclg\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2595-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2595-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p><span style=\"color: #993366;\"><em>There are whole classes of molecules that are synthesized in nature via attack of alkenes on various carbocations.\u00a0 \u00a0One of the most prominent classes is terpenes.\u00a0 <\/em><em>I don&#8217;t want to get into it in this article, but if you are looking for a good time, I strongly suggest looking at how the <a style=\"color: #993366;\" href=\"https:\/\/en.wikipedia.org\/wiki\/Lanosterol\">steroid skeleton of lanosterol is built up from the cyclization of squalene<\/a>. <\/em><\/span>[<a href=\"#notefour\"><span style=\"color: #ff0000;\">Note 5<\/span><\/a>]<\/p>\n<p>This isn&#8217;t the cyclization of an alkene, but it&#8217;s another example of how rearrangements can occur in nature. In this example we start with alpha-pinene, one of the main ingredients in pine oil.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35573\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35573\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35573\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35573\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35573\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35573 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35573\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-j7qtg\" data-id=\"j7qtg\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2596-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2596-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<h2><a id=\"eight\"><\/a>8. Summary<\/h2>\n<ul>\n<li>HCl, HBr, and HI will all add to alkenes. The alkene acts as a\u00a0<strong>nucleophile<\/strong>, forming a bond with the electrophilic proton of the acid.<\/li>\n<li>The reaction always occurs so as to form the most stable carbocation. This is responsible for the observations that led Markovnikov to postulate his rule in the first place.<\/li>\n<li>Be alert for the possibility of carbocation rearrangements when a more stable carbocation can be formed. This can sometimes even occur between carbons with similar substitution if it results in a resonance-stabilized carbocation.<\/li>\n<li>The reaction of HX with alkenes is essentially the same as the reaction of H3O+ with alkenes. They both follow what I call the Carbocation Pathway, one of the three key &#8220;buckets&#8221; of alkene reaction mechanisms that you might find helpful to remember. (<span style=\"color: #800080;\"><em>See &#8211; <a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/02\/22\/addition-pattern-1-the-carbocation-pathway\/\">Alkene Addition Reactions &#8211; The &#8220;Carbocation&#8221; Pathway<\/a><\/em><\/span>)<\/li>\n<\/ul>\n<hr \/>\n<h2><strong><a id=\"notes\"><\/a>Notes<\/strong><\/h2>\n<div class=\"related-articles\"><p><strong>Related Articles<\/strong><\/p><ul><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2023\/09\/15\/hydration-alkenes-acid\/\" class=\"\"><span>Acid-Catalyzed Addition of H2O To Alkenes<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/02\/22\/addition-pattern-1-the-carbocation-pathway\/\" class=\"\"><span>Addition Pattern #1: The \u201cCarbocation Pathway\u201d<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/03\/20\/alkene-addition-pattern-2-the-three-membered-ring-pathway\/\" class=\"\"><span>Alkene Addition Pattern #2: The \u201cThree-Membered Ring\u201d Pathway<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/04\/02\/epoxidation-hydroxylation-cyclopropanation-alkene-mechanism\/\" class=\"\"><span>Alkene Addition Pattern #3: The \u201cConcerted\u201d Pathway<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/02\/26\/rearrangements-in-alkene-addition-reactions\/\" class=\"\"><span>Rearrangements in Alkene Addition Reactions<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/01\/22\/alkene-addition-regioselectivity-syn-anti\/\" class=\"\"><span>Alkene Addition Reactions: \u201cRegioselectivity\u201d and \u201cStereoselectivity\u201d (Syn\/Anti)<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/organic-chemistry-practice-problems\/alkene-reactions-practice-problems\/\" class=\"\"><span>Alkene Reactions Practice Problems (MOC Membership)<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/09\/10\/types-of-isomers\/\" class=\"\"><span>Types of Isomers: Constitutional Isomers, Stereoisomers, Enantiomers, and Diastereomers<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/03\/11\/3-factors-that-stabilize-carbocations\/\" class=\"\"><span>3 Factors That Stabilize Carbocations<\/span><\/a><\/li><\/ul><\/div>\n<p><a id=\"noteone\"><\/a><strong>Note 1. <\/strong>When <strong>peroxides <\/strong>(often written RO-OR) are present a very different reaction pathway occurs, where free-radical intermediates are involved. These reactions are anti-Markovnikov selective.<span style=\"color: #993366;\"><em> For more on this reaction, see <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/04\/12\/addition-hbr-alkenes-roor-peroxides-free-radical\/\">Free-Radical Addition of HBr To Alkene<\/a>s.\u00a0<\/em><\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35583\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/F1-alkenes-plus-HBr-with-peroxides-and-light-will-give-anti-markovnikov-free-radical-addition-of-HBr-across-alkenes.gif\" alt=\"alkenes plus HBr with peroxides and light will give anti markovnikov free radical addition of HBr across alkenes\" width=\"640\" height=\"253\" \/><\/a><\/p>\n<p><strong><a id=\"notetwo\"><\/a>Note 2.\u00a0<\/strong>Telling a small fib here, as this reaction does not <em>always<\/em> lack stereoselectivity. One particularly interesting set of results was in the addition of HBr to 1,2-dimethylcyclohexene in (the very non-polar solvent) pentane. It was found that addition occurred rapidly to give almost exclusively the\u00a0<em>trans<\/em> product; letting it sit around for awhile led to some equilibration between stereoisomers.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35587\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/F2-termolecular-addition-of-HBr-to-cycloalkenes-gives-anti-products-and-a-termolecular-transition-state.gif\" alt=\"termolecular addition of HBr to cycloalkenes gives anti products and a termolecular transition state\" width=\"640\" height=\"325\" \/><\/a><\/p>\n<p>The authors propose that the reaction proceeds through a\u00a0<em>termolecular<\/em> transition state (i.e. involving three molecules) with the alkene sandwiched between two molecules of HBr.<\/p>\n<p><strong><a id=\"notethree\"><\/a>Note 3.\u00a0<\/strong>For our purposes, drawing the immediate formation of a carbocation is fine. Some studies look for the possibility of an even earlier intermediate called a &#8220;pi complex&#8221;, where H+ is coordinated to the pi-bond.\u00a0 As the bond between the pi-bond to the proton becomes stronger, the pi-complex then evolves into the carbocation intermediate.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35588\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/F3-one-postulated-intermediate-of-HX-addition-to-alkenes-is-an-intermediate-pi-complex-of-protium.gif\" alt=\"one postulated intermediate of HX addition to alkenes is an intermediate pi complex of protium\" width=\"640\" height=\"215\" \/><\/a><\/p>\n<p><strong><a id=\"notefour\"><\/a>Note 4.\u00a0<\/strong>Alkenes present a little bit of a dilemma in using curved arrows to describe the movement of electron pairs, since the double bond is not polarized and there is no obvious nucleophilic or electrophilic end. The convention in drawing arrows is that the carbon involved in bond formation is the one closest to the electrophile.<\/p>\n<p>For example here is an example of arrow-pushing that shows the right-hand carbon of the double bond forming a new bond to H:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35584\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/F4-with-arrow-pushing-and-alkene-addition-there-is-the-possibility-of-ambiguity-in-determining-which-bond-is-formed-depends-on-direction-of-arrow.gif\" alt=\"with arrow pushing and alkene addition there is the possibility of ambiguity in determining which bond is formed - depends on direction of arrow\" width=\"640\" height=\"203\" \/><\/a><\/p>\n<p>And here is an example of curved arrows showing formation of a new bond to the left side of the alkene:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35585\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/09\/F5-ambiguity-of-arrow-pushing-with-alkene-addition-.gif\" alt=\"-ambiguity of arrow pushing with alkene addition\" width=\"640\" height=\"222\" \/><\/a><\/p>\n<p>To solve this dilemma, various new conventions have been devised such as the <a href=\"\" class=\"custom-tooltip\" data-image=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/10\/Supp-1-the-bouncy-arrow-convention-for-removing-arrow-pushing-ambiguity.gif\" data-link=\"\" data-title=\"\" data-text=\"\">bouncy arrow formalism <\/a> and <a href=\"\" class=\"custom-tooltip\" data-image=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/10\/Supp-2-the-dashed-arrow-convention-for-removing-arrow-pushing-ambiguity.gif\" data-link=\"\" data-title=\"\" data-text=\"\">drawing a dashed line<\/a> to indicate the bond being formed, although these have not exactly taken the world by storm.<\/p>\n<p><strong><a id=\"notefive\"><\/a>Note 5.<\/strong> If you are looking for a good time, <a href=\"#reften\">this review<\/a> outlines the whole rich and fascinating history of &#8220;cationic&#8221; alkene cyclizations, with a particular focus on how steroids and other related compounds are synthesized in nature.<\/p>\n<hr \/>\n<h2><strong><a id=\"quiz\"><\/a>Quiz Yourself!<\/strong><\/h2>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/0618-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3594-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3612-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3613-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2667-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2668-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/0632-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2604-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2603-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2602-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n<hr \/>\n<h2><strong><a id=\"references\"><\/a>(Advanced) References and Further Reading<\/strong><\/h2>\n<p>Ingold&#8217;s &#8220;<a href=\"https:\/\/archive.org\/details\/structuremechani0000ingo\">Structure and Mechanism in Organic Chemistry<\/a>&#8221; is a valuable guide to the early literature on this topic.<\/p>\n<ol>\n<li><strong>The Logic Behind Markovnikov&#8217;s Rule: Was It an Inspired Guess? \u2026No!<\/strong><br \/>\nD. E. Lewis,\u00a0<i>Angew. Chem. Int. Ed.<\/i>\u00a0<b>2021<\/b>,\u00a0<i>60<\/i>, 4412.<br \/>\n<strong>DOI: <\/strong><a href=\"https:\/\/doi.org\/10.1002\/anie.202008228\">10.1002\/anie.202008228<\/a><br \/>\nFun, accessible historical essay examining Markovnikov&#8217;s studies in the 1860&#8217;s-1870&#8217;s.<\/li>\n<li><strong>I. Ueber die Abh\u00e4ngigkeit der verschiedenen Vertretbarkeit des Radicalwasserstoffs in den isomeren Butters\u00e4uren.<\/strong><br \/>\nMarkownikoff, W. (1870)<br \/>\n<em>Justus Liebigs Ann. Chem.<\/em>, 153: 228-259.<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/doi.org\/10.1002\/jlac.18701530204\">10.1002\/jlac.18701530204<\/a><br \/>\nThe original Markovnikov paper.<\/li>\n<li><strong>ELECTRON DISPLACEMENT IN CARBON COMPOUNDS I. ELECTRON DISPLACEMENT VERSUS ALTERNATE POLARITY IN ALIPHATIC COMPOUNDS<\/strong><br \/>\nHoward J. Lucas and Archibald Y. Jameson<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1924<\/strong> 46 (11), 2475-2482<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/pdf\/10.1021\/ja01676a018\">10.1021\/ja01676a018<\/a><br \/>\nIf not the earliest explanation of Markovnikov&#8217;s rule, certainly one of them.<\/li>\n<li><strong><a id=\"reffour\"><\/a>Secondary Isoamyl Chloride, 3-Chloro-2-methylbutane<\/strong><br \/>\nFrank C. Whitmore and Franklin Johnston<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1933<\/strong> 55 (12), 5020-5022<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja01339a053\">10.1021\/ja01339a053\u00a0<\/a><br \/>\nOne of the first clearly written out explanations of a carbocation rearrangement in addition of HX to alkenes. A subsequent paper ( <a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/ja01160a023\">JACS 1950<\/a> 1511) goes into more detail.<\/li>\n<li><strong>The Stereochemistry of the Addition of Hydrogen Bromide to 1,2-Dimethylcyclohexene<\/strong><br \/>\nGeorge S. Hammond and Thomas D. Nevitt<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1954<\/strong> 76 (16), 4121-4123<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja01645a020\">10.1021\/ja01645a020\u00a0<\/a><br \/>\nOK. When I wrote, above, that the addition of HX to alkenes is not stereoselective, I fibbed. The truth is that it <strong>can<\/strong> be stereoselective for\u00a0<em>anti<\/em> addition if carried out at low temperatures in non polar solvents such as pentane. \u00a0The proposed mechanism is not a free carbocation but a termolecular transition state involving two equivalents of H-Br. (Interestingly, though, the reaction of H<sub>3<\/sub>O+ with the same compound is <strong>not<\/strong> stereoselective).<br \/>\nIn the strongly polar solvent acetic acid, the reaction results predominantly (but not exclusively!) through the classic carbocation mechanism.<\/li>\n<li><strong>Hydrochlorination of cyclohexene in acetic acid. Kinetic and product studies<\/strong><br \/>\nRobert C. Fahey, Michael W. Monahan, and C. Allen McPherson<br \/>\n<em>Journal of the American Chemical Society<\/em> 1970 92 (9), 2810-2815<br \/>\n<strong>DOI: <\/strong><a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/ja00712a034\">10.1021\/ja00712a034<\/a><br \/>\nDetailed kinetic studies of the addition of HCl to cyclohexene in acetic acid, discussing a possible third-order mechanism (rate = <em>k<\/em>[cyclohexene][HX]<sup>2<\/sup>).<\/li>\n<li><strong>SPIROANNELATION OF ENOL SILANES: <span class=\"chemname\">2-OXO-5-METHOXYSPlRO[5.4]DECANE<br \/>\n<\/span><\/strong>Lee, T. V.; Porter, J. R.<br \/>\n<em>Org. <\/em><em>Synth.<\/em> <strong>1995<\/strong>, <em>72<\/em>, 189<br \/>\n<strong>DOI<\/strong>: <a href=\"http:\/\/www.orgsyn.org\/demo.aspx?prep=CV9P0643\">10.15227\/orgsyn.072.0189<\/a><br \/>\nThe first reaction in the above procedure involves two steps \u2013 addition of HBr across the double bond and converting the aldehyde to a dimethyl acetal.<\/li>\n<li><strong>Markovnikov&#8217;s Rule<\/strong><br \/>\nRobert C. Kerber<br \/>\n<em>Journal of Chemical Education<\/em> <strong>2007<\/strong> 84 (7), 1109<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ed084p1109.1\">10.1021\/ed084p1109.1\u00a0<\/a><br \/>\nA 2007 missive urging educators and textbook writers to retire the teaching of Markovnikov&#8217;s Rule.<\/li>\n<li><strong><a id=\"reften\"><\/a>A Case Study in Biomimetic Total Synthesis:\u2009 Polyolefin Carbocyclizations to Terpenes and Steroids<\/strong><br \/>\nRyan A. Yoder and Jeffrey N. Johnston<br \/>\n<em>Chemical Reviews<\/em> <strong>2005<\/strong> 105 (12), 4730-4756<br \/>\n<strong>DOI<\/strong>: 10.1021\/cr040623l<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Hydrohalogenation of Alkenes and Markovnikov&#8217;s Rule When hydrohalic acids (HCl, HBr, HI) are added to alkenes, addition reactions can occur, resulting in formation of a <\/p>\n","protected":false},"author":1,"featured_media":35582,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1418],"tags":[889,169,299,360,887,890],"post_folder":[],"class_list":["post-6981","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-alkene-reactions","tag-addition-reactions","tag-alkenes","tag-alkyl-halides","tag-markovnikoff","tag-markovnikov","tag-most-substituted"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Hydrohalogenation of Alkenes and Markovnikov&#039;s Rule &#8211; 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