{"id":10599,"date":"2017-03-22T15:43:02","date_gmt":"2017-03-22T19:43:02","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=10599"},"modified":"2026-04-17T21:07:55","modified_gmt":"2026-04-18T02:07:55","slug":"reactions-of-dienes-12-and-14-addition","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2017\/03\/22\/reactions-of-dienes-12-and-14-addition\/","title":{"rendered":"Reactions of Dienes: 1,2 and 1,4 Addition"},"content":{"rendered":"<p><strong>Kinetic Versus Thermodynamic Control In Addition of HBr to Dienes: 1,2- and 1,4- Addition<\/strong><\/p>\n<p>In today&#8217;s post we&#8217;ll discuss \u00a01,2- and 1,4- addition to dienes &#8211; specifically, the addition of strong acid such as HBr.<\/p>\n<ul>\n<li>When a diene undergoes reaction with a strong acid like HBr, protonation results in a\u00a0<strong>resonance-stabilized\u00a0<\/strong>carbocation<\/li>\n<li>The resonance-stabilized carbocation can undergo attack at\u00a0<strong>two\u00a0<\/strong>possible positions.<\/li>\n<li>When the reaction is conducted at <strong>low<\/strong> temperatures, the reaction is <strong>irreversible <\/strong>and the major product will be the one with the lowest-energy transition state, which is the carbon best able to stabilize positive charge.<\/li>\n<li>This is referred to as running the reaction under\u00a0<strong>kinetic control<\/strong>.<\/li>\n<li>When the reaction is conducted at higher temperatures, the reaction is\u00a0<strong>reversible\u00a0<\/strong>and the major product will be the one which is most\u00a0<strong>thermodynamically stable<\/strong>, which is generally the\u00a0<strong>most-substituted\u00a0<\/strong>alkene.<\/li>\n<li>This is referred to as running the reaction under\u00a0<strong>thermodynamic control<\/strong>.<\/li>\n<\/ul>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-15592\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/0-summary-of-12-and-14-addition-with-addition-of-hbr-to-butadiene-thermodynamic-versus-kinetic-product-varies-with-temperature-kinetic-versus-thermodynamic-control.gif\" alt=\"summary of 12 and 14 addition with addition of hbr to butadiene thermodynamic versus kinetic product varies with temperature kinetic versus thermodynamic control\" width=\"600\" height=\"599\" \/><\/p>\n<p><strong>Table of Contents<\/strong><\/p>\n<ol>\n<li><a href=\"#one\">Addition To Alkenes, Revisited<\/a><\/li>\n<li><a href=\"#two\">Reaction Of Butadiene With Acid Gives &#8220;1,2-Addition&#8221; And &#8220;1,4-Addition&#8221; Products<\/a><\/li>\n<li><a href=\"#three\">The &#8220;1,4 Addition&#8221; Product Of Acids Adding To Butadiene<\/a><\/li>\n<li><a href=\"#four\">Protonation Of Butadiene Gives A Resonance-Stabilized Carbocation<\/a><\/li>\n<li><a href=\"#five\">The Effect Of Temperature: Low Temperatures Give &#8220;1,2&#8221; Addition To Butadiene<\/a><\/li>\n<li><a href=\"#six\">Higher Temperatures Give More Of The &#8220;1,4&#8221; Product<\/a><\/li>\n<li><a href=\"#seven\">With Butadiene, The &#8220;1,4&#8221; Product Is More Stable Because It Has A More Substituted Double Bond<\/a><\/li>\n<li><a href=\"#eight\">&#8220;Kinetic Control&#8221; vs &#8220;Thermodynamic Control&#8221;: At Low Temperatures The Reaction Is Irreversible And Products Are Determined By Relative Rates<\/a><\/li>\n<li><a href=\"#nine\">Thermodynamic Control: At Higher Temperatures The Reaction Is Reversible And Product Distribution Is Determined By Stability<\/a><\/li>\n<li><a href=\"#ten\">Using An Energy Diagram To Understand Thermodynamic Versus Kinetic Control<\/a><\/li>\n<li><a href=\"#eleven\">A Parting Word Of Warning: The &#8220;1,4-Product&#8221; Is Not Always The &#8220;Thermodynamic&#8221; Product<\/a><\/li>\n<li><a href=\"#twelve\">Other Reactions Can Give 1,2- and 1,4- Additions As Well<\/a><\/li>\n<li><a href=\"#notes\">Notes<\/a><\/li>\n<li><a href=\"#quizzes\">Quiz Yourself!<\/a><\/li>\n<li><a href=\"#references\">(Advanced) References and Further Reading<\/a><\/li>\n<\/ol>\n<hr \/>\n<h2><strong><a id=\"one\"><\/a>1. Addition To Alkenes, Revisited<\/strong><\/h2>\n<p>Waaay back in the day we talked about addition reactions of alkenes. Remember\u00a0<a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/02\/08\/markovnikovs-rule-1\/\">Markovnikov&#8217;s rule<\/a>\u00a0in the addition of electrophiles to alkenes?<\/p>\n<p>For example, take an alkene like 1-butene, and add HBr. What happens?<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-15593\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/1-review-the-addition-of-acids-to-alkenes-with-hbr-giving-alkyl-bromides-also-works-for-hi-and-h2o-follows-markovnikovs-rule.gif\" alt=\"review the addition of acids to alkenes with hbr giving alkyl bromides also works for hi and h2o follows markovnikovs rule\" width=\"600\" height=\"195\" \/><\/p>\n<p>An addition reaction occurs! (Break C-C pi, and form adjacent C-H and C-Br bonds).<\/p>\n<p>Bromine adds to the most substituted carbon of the alkene, and hydrogen adds to the least substituted carbon. That&#8217;s due to carbocation stability: the reaction proceeds through <a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/03\/11\/3-factors-that-stabilize-carbocations\/\">the most stable carbocation<\/a>, which happens to be the most substituted.<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-15594\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/2-example-of-markovnikov-rule-with-1-butene-step-1-attack-hydrogen-of-hbr-resulting-in-more-substituted-carbocation-followed-by-attack-of-bromide-ion-to-give-alkyl-bromide.gif\" alt=\"example of markovnikov rule with 1-butene step 1 attack hydrogen of hbr resulting in more substituted carbocation followed by attack of bromide ion to give alkyl bromide\" width=\"600\" height=\"237\" \/><\/p>\n<h2><a id=\"two\"><\/a>2. Reaction Of Butadiene With Acid Gives &#8220;1,2-Addition&#8221; And &#8220;1,4-Addition&#8221; Products<\/h2>\n<p>All well and good. But since we&#8217;ve been discussing <a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/01\/24\/conjugation-and-resonance\/\">conjugation and resonance,<\/a> let&#8217;s throw in an additional wrinkle.<\/p>\n<p>What happens when we try the same reaction on a <strong>diene?\u00a0<\/strong>Butadiene, for example.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15595\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/3-question-what-happens-when-butadiene-is-treated-with-hbr-what-product-do-you-get.gif\" alt=\"question what happens when butadiene is treated with hbr what product do you get\" width=\"600\" height=\"166\" \/><\/p>\n<p>I&#8217;ll tell you. You get two products! (But the second one might not be what you think it is).<\/p>\n<p>Here&#8217;s what they look like:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15596\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/4-when-butadiene-is-treated-with-hbr-two-products-result-we-call-these-12-and-14-addition-the-12-product-is-formed-at-lower-temperature-the-14-product-formed-at-higher-temperature.gif\" alt=\"when butadiene is treated with hbr two products result we call these 12 and 14 addition the 12 product is formed at lower temperature the 14 product formed at higher temperature\" width=\"600\" height=\"302\" \/><\/p>\n<p>Product #1 is essentially the same product that we saw\u00a0in the 1-butene example: \u00a0H and Br are added across two consecutive carbons of a double bond. Note that since butadiene is symmetric, \u00a0the same product is formed <em>regardless<\/em> of which double bond participates! (we get 3-bromo-1-butene either way).<\/p>\n<p>Since addition occurs across <strong>two consecutive carbons<\/strong>, we often call this &#8220;1,2 addition&#8221;.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15597\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/5-definition-of-12-addition-in-addition-of-hbr-to-butadiene-the-hydrogen-ends-up-on-carbon-1-and-the-bromine-ends-up-on-carbon-2-adds-to-adjacent-carbons.gif\" alt=\"definition of 12 addition in addition of hbr to butadiene the hydrogen ends up on carbon 1 and the bromine ends up on carbon 2 adds to adjacent carbons\" width=\"600\" height=\"256\" \/><\/p>\n<h2><a id=\"three\"><\/a>3. The &#8220;1,4 Addition&#8221; Product Of Acids Adding To Butadiene<\/h2>\n<p>In contrast, Product #2 shows the result of adding H and Br across\u00a0<em>four<\/em> conjugated carbons. All four carbons participate in the reaction. \u00a0A new C-H single bond has formed on one end of the diene (C-1), and C-Br formed on the other end (C-4). Note that the C<sub>1<\/sub>-C<sub>2<\/sub> and C<sub>3<\/sub>-C<sub>4<\/sub> pi bonds are broken, and we&#8217;ve formed a new pi bond between C<sub>2<\/sub> and C<sub>3<\/sub>.<\/p>\n<p>We call this &#8220;1,4 addition&#8221;.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15598\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/6-definition-of-14-addition-in-addition-of-hbr-to-butadiene-the-h-ends-up-attached-to-carbon-1-and-the-bromine-ends-up-attached-to-carbon-4-hence-14-addition-internal-alkene.gif\" alt=\"definition of 14 addition in addition of hbr to butadiene the h ends up attached to carbon 1 and the bromine ends up attached to carbon 4 hence 14 addition internal alkene\" width=\"600\" height=\"257\" \/><\/p>\n<p><span style=\"color: #993366;\"><em>[Note: to simplify the discussion here, I&#8217;m choosing to\u00a0ignore double bond isomers (i.e.\u00a0E\u00a0and\u00a0Z) in this analysis.\u00a0\u00a0In the lab, the 1,4- example above will exist as a mixture of (mostly)\u00a0E product with a small amount of the\u00a0Z. ]<\/em><\/span><\/p>\n<p>So why does this &#8220;1,4 addition&#8221; happen in the first place? What&#8217;s different about butadiene, as opposed to 1-butene where only &#8220;1,2-addition&#8221; was possible?<\/p>\n<h2><a id=\"four\"><\/a>4. Protonation Of Butadiene Gives A Resonance-Stabilized Carbocation<\/h2>\n<p>The first thing to notice is that the initial protonation of butadiene gives a\u00a0<strong>resonance-stabilized carbocation<\/strong>. See how protonation of C-1 gives a carbocation that has two important resonance forms?<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15599\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/7-protonatoin-of-butadiene-gives-carbocation-that-is-resonance-stabilized-with-major-and-minor-resonance-contributors-depending-on-substitution-of-carbocation-recall-resonance-hybrid.gif\" alt=\"protonatoin of butadiene gives carbocation that is resonance stabilized with major and minor resonance contributors depending on substitution of carbocation recall resonance hybrid\" width=\"630\" height=\"203\" \/><\/p>\n<p>In the case of butadiene,<\/p>\n<ul>\n<li>the <strong>major contributor<\/strong>\u00a0to the resonance hybrid will be the resonance form where the carbocation is on the more substituted carbocation (C<sub>2<\/sub>)<\/li>\n<li>the <strong>minor contributor<\/strong> will be the resonance form where the carbocation is on the less substituted carbocation (C<sub>4<\/sub>).<\/li>\n<\/ul>\n<p>Attack of the nucleophile (Br<sup>\u2013<\/sup>) at the C<sub>2<\/sub> position of the hybrid will lead to the 1,2-product.<\/p>\n<p>Attack of Br<sup>\u2013\u00a0<\/sup>at the C<sub>4<\/sub> position of the resonance hybrid will lead to the 1,4-product.<\/p>\n<p>We can draw it up like this:<a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2017\/03\/4-12-and-14-addition-1-e1489779494116.png\"><br \/>\n<\/a><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15609\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/8-intermediate-from-protonation-of-butadiene-with-hcl.gif\" alt=\"intermediate from protonation of butadiene with hcl\" width=\"600\" height=\"357\" \/><\/p>\n<p><span style=\"color: #993366;\"><em>[Note: never forget\u00a0that <strong>resonance forms <\/strong>are<strong> not <\/strong>in<strong> equilibrium <\/strong>with each other.\u00a0It&#8217;s understandable to\u00a0casually say that &#8220;Br(\u2013) will attack the top\u00a0resonance form with the more stable carbocation&#8221; so long as you remember that the true structure of the molecule is a <strong>hybrid<\/strong> of the two resonance forms.] In the <a style=\"color: #993366;\" href=\"#noteone\">footnote<\/a>, I&#8217;m including perhaps a more correct way to show formation of the bottom resonance form.<\/em><\/span><\/p>\n<h2><strong><a id=\"five\"><\/a>5. The Effect Of Temperature: Low Temperatures Give &#8220;1,2&#8221; Addition To Butadiene<\/strong><\/h2>\n<p>Here&#8217;s the big question: which one of the two products will be major? The 1,2-addition product or the 1,4-addition product?<\/p>\n<p>We&#8217;re so used to seeing &#8220;Markovnikov addition&#8221; in alkenes (where addition occurs to the most stable carbocation) that it seems intuitive that the 1,2-addition product would be dominant.<\/p>\n<p>And indeed, at low temperature, 1,2 addition to butadiene is favoured. Here&#8217;s a literature example.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15600\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/9-low-temperature-addition-of-hbr-to-butadiene-gives-12-addition-about-80-per-cent-at-minus-80-degrees.gif\" alt=\"low temperature addition of hbr to butadiene gives 12 addition about 80 per cent at minus 80 degrees\" width=\"600\" height=\"243\" \/><\/p>\n<h2><strong><a id=\"six\"><\/a>6. Higher Temperatures Give More Of The &#8220;1,4&#8221; Product<\/strong><\/h2>\n<p>Interestingly, however, as the temperature is increased, <strong>the amount of 1,4 product increases<\/strong>.<\/p>\n<p>At room temperature, the ratio of 1,2- and 1,4- addition is 45:55 .<\/p>\n<p>At 40 degrees Celsius the 1,4- product is dominant (about 80%).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15601\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/10-at-higher-temperature-addition-of-hbr-to-butadiene-gives-14-addition-at-40-degrees-celsius-addition-of-hbr-to-butadiene-80-per-cent-14.gif\" alt=\"at higher temperature addition of hbr to butadiene gives 14 addition at 40 degrees celsius addition of hbr to butadiene 80 per cent 14\" width=\"600\" height=\"243\" \/><\/p>\n<h2><a id=\"seven\"><\/a>7. With Butadiene, The &#8220;1,4&#8221; Product Is More Stable Because It Has A More Substituted Double Bond<\/h2>\n<p>What&#8217;s going on here? What structural features are present that could possibly make formation of the 1,4 product more favourable\u00a0than the 1,2 product, even though it goes through a &#8220;less stable&#8221; carbocation?<\/p>\n<p>The answer lies in the <strong>substitution pattern of the double bond<\/strong>.<\/p>\n<p>Remember <a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/08\/31\/elimination-reactions-2-zaitsevs-rule\/\">Zaitsev&#8217;s rule<\/a>? Same deal.\u00a0The 1,4 product is more stable because it is a more substituted double bond.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15602\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/11-recall-that-stability-of-alkenes-increases-as-number-of-attached-carbons-increases-12-has-monosubstituted-double-bond-14-has-disubstituted-double-bond.gif\" alt=\"recall that stability of alkenes increases as number of attached carbons increases 12 has monosubstituted double bond 14 has disubstituted double bond\" width=\"600\" height=\"257\" \/><\/p>\n<p>The 1,4 product has a\u00a0<em>di-<\/em>substituted double bond, whereas the 1,2-product has a \u00a0<em>mono-<\/em>substituted double bond. Generally speaking, double bond stability increases as the number of carbons directly attached to the double bond is increased. (<span style=\"color: #993366;\"><em>See article: <a href=\"https:\/\/www.masterorganicchemistry.com\/2020\/04\/30\/alkene-stability\/\">Alkene Stability<\/a><\/em><\/span>)<\/p>\n<p>So why would 1,4 be more favoured under conditions of higher temperature, and the 1,2 be favoured under conditions of lower temperature?<\/p>\n<h2><strong><a id=\"eight\"><\/a>8. &#8220;Kinetic Control&#8221; vs &#8220;Thermodynamic Control&#8221;: At Low Temperatures The Reaction Is Irreversible And Products Are Determined By Relative Rates<\/strong><\/h2>\n<p>At low temperatures, the differentiating factor is the relative energies of the transition states leading to the products. The 1,2 product has a lower-energy transition state, owing to the fact that charge is more stable on the more substituted carbon. The difference between the energies of these transition states will determine the product ratio.<\/p>\n<p><em><span style=\"color: #993366;\">A quick analogy. Imagine you&#8217;re hungry, and you only have $5 in your pocket. In a choice between McDonalds and Applebee&#8217;s, the only accessible option is McDonalds &#8211; even if, for some reason, you like Applebee&#8217;s a lot more.<\/span><br \/>\n<\/em><\/p>\n<p>Let&#8217;s sketch this out. The carbocation intermediate can pass through the two different transition states \u00a0that lead to the 1,2- and 1,4- products, respectively. If we choose a temperature low enough, then the product distribution will reflect the difference in energy between the two activation energies E<sub>a<\/sub> (1,2) and E<sub>a<\/sub> (1,4).\u00a0<em>So long as the reaction is not reversible<\/em>, the product with the lower energy transition state will dominate. This is called &#8220;<strong>kinetic contro<\/strong>l&#8221;.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15608\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/12-reaction-energy-diagram-of-kinetic-control-low-temperature-12-transition-state-and-14-transition-state-activation-energy-less-for-12-addition.gif\" alt=\"reaction energy diagram of kinetic control low temperature 12 transition state and 14 transition state activation energy less for 12 addition\" width=\"630\" height=\"434\" \/><\/p>\n<h2><a id=\"nine\"><\/a>9. Thermodynamic Control: At Higher Temperatures The Reaction Is Reversible And Product Distribution Is Determined By Stability<\/h2>\n<p>At higher temperatures, the reaction has the potential to be\u00a0<strong>reversible.<\/strong> [<a href=\"#notetwo\">Note 2<\/a>]<strong>\u00a0<\/strong>In this case, this means is that both the 1,2- and 1,4- products can\u00a0<em>ionize\u00a0<\/em>(think of the first step in the S<sub>N<\/sub>1 reaction), reforming the carbocation intermediate.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15603\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/13-at-high-enough-temperatures-12-product-is-reversible-can-go-back-to-resonance-stabilized-carbocaiton-intermediate.gif\" alt=\"at high enough temperatures 12 product is reversible can go back to resonance stabilized carbocaiton intermediate\" width=\"600\" height=\"223\" \/><\/p>\n<p>This sets up an\u00a0<strong>equilibrium<\/strong><em>.\u00a0<\/em>The product ratio will now reflect the relative stabilities of the 1,2- and 1,4- <strong>products,<\/strong> not the transition states leading to their formation. In the case of butadiene, since the 1,4- product is more stable (it has a disubstituted double bond) it will be the dominant product at higher temperatures.<\/p>\n<p>This is referred to as &#8220;<strong>thermodynamic control<\/strong>&#8220;.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15604\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/14-at-high-temperatures-there-is-equilibrium-between-12-product-and-14-product-which-is-called-thermodynamic-control.gif\" alt=\"at high temperatures there is equilibrium between 12 product and 14 product which is called thermodynamic control\" width=\"600\" height=\"228\" \/><\/p>\n<p>Math interlude: \u00a0recall that \u0394G = \u2013RT lnK<\/p>\n<p>A difference of 1 kcal\/mol in stability doesn&#8217;t sound like much, but it translates into a 83:17\u00a0ratio of products at equilibrium at room temperature.<\/p>\n<p><span style=\"color: #993366;\"><em>Continuing our analogy: with enough\u00a0money in your pocket, the decision where to eat lunch is more a function of how much you like the overall McDonalds vs. Applebee&#8217;s experiences, not how much they cost.\u00a0<\/em><\/span><\/p>\n<h2><a id=\"ten\"><\/a>10. Using An Energy Diagram To Understand\u00a0Thermodynamic Versus Kinetic Control<\/h2>\n<p>Drawing up the reaction energy diagram can be helpful to understand kinetic and thermodynamic control. <a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/02\/09\/can-opener-economics\/\">This post here<\/a>\u00a0goes\u00a0into more detail, but\u00a0we&#8217;ll repeat the basics here.<\/p>\n<p>The reaction energy diagram for the addition of HBr to butadiene looks like this:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15605\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/15-reaction-energy-diagram-for-12-versus-14-addition-of-hbr-to-butadiene-showing-resonance-stabilized-carbocations-and-reversibility-to-12-and-14-products.gif\" alt=\"reaction energy diagram for 12 versus 14 addition of hbr to butadiene showing resonance stabilized carbocations and reversibility to 12 and 14 products\" width=\"630\" height=\"389\" \/><\/p>\n<p>Point\u00a0<strong>A<\/strong> is the starting butadiene, and point\u00a0<strong>B<\/strong> is the transition state for addition of H to butadiene.<\/p>\n<p>The important part to pay attention to is the &#8220;local minimum&#8221; <strong>C<\/strong>, the resonance-stabilized carbocation.<\/p>\n<p>As we mentioned previously, going from intermediate\u00a0<strong>C<\/strong> to transition states\u00a0<strong><span style=\"color: #339966;\">D<\/span>\u00a0<\/strong>and\u00a0<strong><span style=\"color: #0000ff;\">D<\/span>\u00a0<\/strong>represent the energy pathways\u00a0for 1,2- and 1,4- addition, respectively.<\/p>\n<p>Hence the\u00a0activation energies for the forward reactions is equal to the difference in energy between\u00a0<strong><span style=\"color: #339966;\">D<\/span>\u00a0<\/strong>and <strong>C <\/strong>(for 1,2-addition)\u00a0and \u00a0<strong><span style=\"color: #0000ff;\">D\u00a0<\/span><\/strong><span style=\"color: #000000;\">and\u00a0<strong>C<\/strong> (for 1,4-addition). We saw that 1,2-addition has a lower activation energy.\u00a0<\/span><\/p>\n<p>Now let&#8217;s look at the reverse reaction.<\/p>\n<p>Points <strong><span style=\"color: #339966;\">E<\/span>\u00a0<\/strong>and\u00a0<strong><span style=\"color: #0000ff;\">E<\/span>\u00a0<\/strong>represent the energies of the 1,2- and 1,4- products.<\/p>\n<p>The activation energy for the\u00a0<strong><em>reverse<\/em>\u00a0<\/strong>reaction is the difference in energy between\u00a0<strong><span style=\"color: #339966;\">E<\/span>\u00a0<\/strong>and transition state\u00a0<span style=\"color: #339966;\"><strong>D<\/strong><\/span>, and\u00a0<strong><span style=\"color: #0000ff;\">E<\/span>\u00a0<\/strong>and transition state\u00a0<span style=\"color: #0000ff;\"><strong>D<\/strong><\/span>, respectively.<\/p>\n<p>It should be clear from this diagram that the activation energies for the forward reaction \u00a0(going from <strong>C<\/strong>\u00a0through transition states <strong><span style=\"color: #339966;\">D<\/span>\u00a0<\/strong>and\u00a0<strong><span style=\"color: #0000ff;\">D\u00a0<\/span><\/strong><span style=\"color: #000000;\">give<\/span> <strong><span style=\"color: #339966;\">E<\/span>\u00a0<\/strong>and\u00a0<strong><span style=\"color: #0000ff;\">E<\/span><\/strong><span style=\"color: #000000;\">, respectively<\/span>)\u00a0\u00a0are much lower than the activation energies going in the reverse reaction (i.e. from <strong><span style=\"color: #339966;\">E<\/span>\u00a0<\/strong>and\u00a0<strong><span style=\"color: #0000ff;\">E\u00a0<\/span><\/strong><span style=\"color: #0000ff;\"><span style=\"color: #000000;\">through transition states\u00a0<strong><span style=\"color: #339966;\">D<\/span>\u00a0<\/strong>and\u00a0<span style=\"color: #0000ff;\"><strong>D<\/strong><\/span><\/span><\/span>\u00a0back to carbocation\u00a0<strong>C<\/strong>\u00a0).<\/p>\n<ul>\n<li>So if we keep the temperature low, we favor the forward reaction and hinder the reverse, and obtain the\u00a0<strong>kinetic\u00a0product.\u00a0<\/strong><\/li>\n<li>If the temperature is raised, the reverse reaction becomes energetically accessible, and equilibrium is established. We will then obtain the\u00a0<strong>thermodynamic product.\u00a0<\/strong><\/li>\n<\/ul>\n<h2><strong><a id=\"eleven\"><\/a>11.A Parting Word Of Warning: The &#8220;1,4-Product&#8221; Is Not Always The &#8220;Thermodynamic&#8221; Product<\/strong><\/h2>\n<p>Let&#8217;s summarize.\u00a0\u00a0Understanding the following two factors is key to correctly answering exam problems.<\/p>\n<ol>\n<li><del><\/del>The\u00a0relative importance of the carbocation resonance forms<\/li>\n<li>The relative stabilities of the double bond products.<\/li>\n<\/ol>\n<p>In the case of butadiene, it is true that the\u00a0<strong>1,2<\/strong> product was formed through a more stable carbocation (kinetic product), and the\u00a0<strong>1,4<\/strong> product had a more stable double bond (thermodynamic product).<\/p>\n<p>But it will not always be true for all dienes!!<\/p>\n<p>Here are three\u00a0examples that will help you think through the main issues (<a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/04\/11\/more-on-12-and-14-additions-to-dienes\/\">answers in the next post<\/a>).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15606\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/16-real-life-exam-problems-to-think-through-12-and-14-addition-to-various-dienes-cyclopentadiene-25-dimethyl-2-4-hexadiene-and-also-1-methyl-cyclohexadiene.gif\" alt=\"real life exam problems to think through 12 and 14 addition to various dienes cyclopentadiene 25 dimethyl 2 4 hexadiene and also 1 methyl cyclohexadiene\" width=\"600\" height=\"161\" \/><\/p>\n<h2><a id=\"twelve\"><\/a>12. Other Reactions Can Give 1,2- and 1,4- Additions As Well<\/h2>\n<p>This post is long enough, but I would be remiss if I failed to note that 1,2 and 1,4 additions to dienes are also possible for a few other classes of reaction.<\/p>\n<ul>\n<li>Addition of HBr to dienes under free-radical conditions (e.g. HBr + peroxides)<\/li>\n<li>Addition of Br<sub>2<\/sub> (and Cl<sub>2<\/sub>) to dienes.<\/li>\n<\/ul>\n<p>Note that similar issues will arise (i.e. stability of a reactive intermediate versus stability of the final product). We&#8217;ll go into more detail when the time comes.<\/p>\n<p><em>Many thanks to Tom Struble for help with preparing this post.\u00a0<\/em><\/p>\n<hr \/>\n<h2><a id=\"notes\"><\/a>Notes<\/h2>\n<div class=\"related-articles\"><p><strong>Related Articles<\/strong><\/p><ul><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/02\/09\/kinetic-thermodynamic-products-can-openers\/\" class=\"\"><span>Thermodynamic and Kinetic Products<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/04\/11\/more-on-12-and-14-additions-to-dienes\/\" class=\"\"><span>More On 1,2 and 1,4 Additions To Dienes<\/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><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2020\/04\/30\/alkene-stability\/\" class=\"\"><span>Alkene Stability<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/08\/31\/elimination-reactions-2-zaitsevs-rule\/\" class=\"\"><span>Elimination Reactions (2): The Zaitsev Rule<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/02\/08\/markovnikovs-rule-1\/\" class=\"\"><span>Markovnikov Addition Of HCl To Alkenes<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/01\/24\/conjugation-and-resonance\/\" class=\"\"><span>Conjugation And Resonance In Organic Chemistry<\/span><\/a><\/li><li><\/li><\/ul><\/div>\n<p><strong><a id=\"noteone\"><\/a>Note 1. <\/strong>All the textbooks I consulted showed diagrams similar to what I drew above, with Br(-) attacking different resonance forms. \u00a0Perhaps a more correct way to draw the formation of the carbocation at the 4-position is to show it like this.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15607\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/F1-equivalent-way-to-draw-14-addition-to-butadiene-showing-multiple-arrows.gif\" alt=\"equivalent way to draw 14 addition to butadiene showing multiple arrows\" width=\"600\" height=\"175\" \/><\/p>\n<p><strong><a id=\"notetwo\"><\/a>Note 2.\u00a0<\/strong>Reversibility<\/p>\n<hr \/>\n<h2><a id=\"quizzes\"><\/a>Quiz Yourself!<\/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\/0091-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\/0089-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\/0090-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\/0092-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\/3069-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\/3070-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<ol>\n<li><strong>THE ADDITION OF HYDROGEN CHLORIDE TO BUTADIENE<\/strong><br \/>\nM. S. KHARASCH, J. KRITCHEVSKY, and F. R. MAYO<br \/>\n<em>The Journal of Organic Chemistry<\/em> <strong>1937,<\/strong> <em>02<\/em> (5), 489-496<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/jo01228a010\">10.1021\/jo01228a010<\/a><br \/>\nAn early paper by the esteemed chemist M. S. Kharasch on the addition of HCl to butadiene, seeing whether the ratio of 1,2 to 1,4 addition varied with different reaction conditions.<\/li>\n<li><strong>THE PEROXIDE EFFECT IN THE ADDITION OF REAGENTS TO UNSATURATED COMPOUNDS. XIII. THE ADDITION OF HYDROGEN BROMIDE TO BUTADIENE<\/strong><br \/>\nM. S. KHARASCH, ELLY T. MARGOLIS, and FRANK R. MAYO<br \/>\n<em>The Journal of Organic Chemistry<\/em> <strong>1936,<\/strong> <em>01<\/em> (4), 393-404<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/jo01233a008\">10.1021\/jo01233a008<\/a><br \/>\nAnother early study by M. S. Kharasch in which he studies the addition of HBr to butadiene, in which he attempts to rigorously separate the two modes of addition \u2013 electrophilic vs. radical.<\/li>\n<li><strong>\u2014Mobile-anion tautomerism. Part I. A preliminary study of the conditions of activation of the three-carbon system, and a discussion of the results in relation to the modes of addition to conjugated systems<\/strong><br \/>\nHarold Burton and Christopher Kelk Ingold<br \/>\n<em>J. Chem. Soc.<\/em> <strong>1928<\/strong>, 904-921<br \/>\n<strong>DOI<\/strong>:<a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1928\/jr\/jr9280000904\/unauth#!divAbstract\"> 10.1039\/JR9280000904<\/a><br \/>\nA classic paper from a pioneer of physical organic chemistry, Prof. C. K. Ingold. He suggests the general idea that the 1,2 and 1,4 addition products are in equilibrium and that the 1,2-product can reverse reaction and form the 1,4 product. This is the basis of what we now call &#8220;kinetic&#8221; and &#8220;thermodynamic&#8221; control.<\/li>\n<li><strong> The modes of addition to conjugated unsaturated systems. Part IX. A discussion of mechanism and equilibrium, with a note on three-carbon prototropy<\/strong><br \/>\nP. B. D. de la Mare, E. D. Hughes and C. K. Ingold<br \/>\n<em>J. Chem. Soc.<\/em> <strong>1948<\/strong>, 17<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1948\/jr\/jr9480000017#!divAbstract\">10.1039\/JR9480000017<\/a><br \/>\nHere, C. K. Ingold has reviewed all work (including Kharasch\u2019s) done up to that point in the study of electrophilic additions to conjugated systems.<\/li>\n<li><strong>Properties of conjugated compounds. Part XI. Addition of hydrogen bromide to \u03b2\u03b3- and \u03b1\u03b4-dimethylbutadiene<\/strong><br \/>\nErnest Harold Farmer and Frederick G. B. Marshall<br \/>\n<em>J. Chem. Soc.<\/em> <strong>1931<\/strong>, 129<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1931\/jr\/jr9310000129\/unauth#!divAbstract\">10.1039\/JR9310000129<\/a><br \/>\nWhen methyl groups are added to butadiene, the 1,2 and 1,4 addition ratios can change significantly!\u00a0 This is because the stability of the carbocation intermediates will change.<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Kinetic Versus Thermodynamic Control In Addition of HBr to Dienes: 1,2- and 1,4- Addition In today&#8217;s post we&#8217;ll discuss \u00a01,2- and 1,4- addition to dienes <\/p>\n","protected":false},"author":1,"featured_media":15592,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1163],"tags":[364,365,366,363,998,361,539,362,1192],"post_folder":[],"class_list":["post-10599","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-dienes-and-mo-theory","tag-364","tag-2-addition","tag-4-addition","tag-dienes","tag-energy-diagram","tag-kinetic-control","tag-kinetic-product","tag-thermodynamic-control","tag-thermodynamic-product"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Reactions of Dienes: 1,2 and 1,4 Addition &#8211; Master Organic Chemistry<\/title>\n<meta name=\"description\" content=\"Kinetic and thermodynamic control in addition of HBr to dienes can give 1,2- and 1,4- products. 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How do we explain this? 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