{"id":6849,"date":"2012-12-19T14:22:15","date_gmt":"2012-12-19T19:22:15","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=6849"},"modified":"2025-11-21T11:48:52","modified_gmt":"2025-11-21T17:48:52","slug":"sn1-vs-e1-temperature-sn2-vs-e2","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2012\/12\/19\/sn1-vs-e1-temperature-sn2-vs-e2\/","title":{"rendered":"SN1 vs E1 and SN2 vs E2 : The Temperature"},"content":{"rendered":"<p><strong>SN1 vs E1, and SN2 vs. E2:\u00a0 The Role Of Heat<\/strong><\/p>\n<ul>\n<li>This article assumes you understand the mechanisms of the S<sub>N<\/sub>1\/S<sub>N<\/sub>2\/E1 and E2 reactions. For review, see here [<a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/07\/13\/the-sn1-mechanism\/\">S<sub>N<\/sub>1<\/a>] [<a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/07\/04\/the-sn2-mechanism\/\">S<sub>N<\/sub>2<\/a>] [<a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/09\/19\/the-e1-reaction\/\">E1<\/a>] [<a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/09\/27\/the-e2-mechanism\/\">E2<\/a>]<\/li>\n<li>S<sub>N<\/sub>1\/S<sub>N<\/sub>2\/E1\/E2 reactions tend to happen on <strong>alkyl<\/strong> halides [<em>see <a href=\"https:\/\/www.masterorganicchemistry.com\/2023\/01\/18\/where-will-substitution-elimination-reactions-occur\/\">Identifying Where Substitution and Elimination Reactions Happen<\/a><\/em>]<\/li>\n<li>Determining whether the alkyl halide is <strong>primary<\/strong>, <strong>secondary<\/strong>, <strong>tertiary<\/strong> (or methyl) helps to narrow down the possibilities\u00a0 [<em><span style=\"color: #993366;\">See <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2012\/11\/21\/deciding-sn1sn2e1e2-1-the-substrate\/\">SN1\/SN2\/E1\/E2 &#8211; The Substrate<\/a><\/span>]<\/em><\/li>\n<li>When the nucleophile\/base is\u00a0<strong>negatively charged<\/strong>, the reaction tends to be S<sub>N<\/sub>2\/E2. When the nucleophile\/base is <strong>neutral<\/strong>, the reaction tends to be S<sub>N<\/sub>1\/E1. [<em><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/11\/30\/deciding-sn1sn2e1e2-2-the-nucleophilebase\/\">See SN1\/SN2\/E1\/E2 &#8211; The Nucleophile\/Base<\/a><\/em> ]<\/li>\n<li>If the major reaction pathway cannot be determined by examining these factors, the next useful indicator is to look at the\u00a0<strong>temperature<\/strong>.<\/li>\n<li>Generally, if you are trying to decide between S<sub>N<\/sub>1 and E1 (e.g. for a tertiary alkyl halide with a neutral nucleophile\/base),\u00a0<strong>heat<\/strong> (\u0394 ) indicates <strong>E1<\/strong>, whereas the <strong>absence of heat<\/strong> indicates S<sub>N<\/sub>1<\/li>\n<li>If you are trying to decide between S<sub>N<\/sub>2 and E2 (e.g. for a secondary alkyl halide with a strong base, e.g. HO(-) or RO(-) ) ,\u00a0<strong>heat<\/strong> (\u0394 ) indicates <strong>E2<\/strong>. <em>(<span style=\"color: #800080;\">The absence of heat does <strong>not<\/strong> <strong>necessarily<\/strong> indicate S<sub>N<\/sub>2 &#8211; check with your instructor<\/span>).\u00a0<\/em><\/li>\n<li>Heat may also be indicated in difficult S<sub>N<\/sub>1 reactions (e.g. secondary alkyl halide, neutral nucleophile\/base) where <strong>rearrangements<\/strong> occur.<\/li>\n<\/ul>\n<p><span style=\"color: #993366;\"><em>I also suggest, ahem, pinning down your instructor beforehand on some of these questions because these questions can be subject to a lot of variation.\u00a0<\/em><\/span><\/p>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-35840\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2012\/12\/0-SN1-SN2-E1-E2-The-role-of-heat-and-temperature-in-favoring-elimination-over-substitution.gif\" alt=\"SN1 SN2 E1 E2 - The role of heat and temperature in favoring elimination over substitution\" width=\"640\" height=\"469\" \/><\/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\">The Role of Heat ( \u0394) In Substitution and Elimination Reactions<\/a><\/li>\n<li><a href=\"#two\">Using Temperature to Evaluate SN1 vs. E1<\/a><\/li>\n<li><a href=\"#three\">SN2 vs. E2: Secondary Alkyl Halides<\/a><\/li>\n<li><a href=\"#four\">SN2 vs. E2: Primary Alkyl Halides With Bulky Bases<\/a><\/li>\n<li><a href=\"#five\">SN1 and Secondary Alkyl Halides<\/a><\/li>\n<li><a href=\"#six\">Summary<\/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. The Role of &#8220;Heat&#8221; (\u0394) In Substitution and Elimination Reactions<\/h2>\n<p>Previously we&#8217;ve outlined the main steps in deciding whether a reaction goes through S<sub>N<\/sub>1\/S<sub>N<\/sub>2\/E1\/E2.<span style=\"color: #993366;\"><em> (Note &#8211; it&#8217;s <strong>assumed<\/strong> by this point that if you know the mechanism of the reaction, you should be able to correctly draw the product!)\u00a0<\/em><\/span><\/p>\n<p>These steps are, roughly:<\/p>\n<ul>\n<li>Identify an <strong>sp<sup>3<\/sup> hybridized<\/strong> (alkyl) carbon&#8230;<\/li>\n<li>with a <strong>good leaving group<\/strong>&#8230;<\/li>\n<li>classify the carbon as <strong>primary<\/strong>, <strong>secondary<\/strong> or <strong>tertiary&#8230;<\/strong><\/li>\n<li>identify the <strong>strongest<\/strong> nucleophile\/base in the reaction (<span style=\"color: #800080;\"><em>for our purposes, I will often refer to <strong>negatively charged<\/strong> species as &#8220;<strong>strong<\/strong>&#8221; and <strong>neutral<\/strong> species as &#8220;<strong>weak<\/strong>&#8220;, although there are some exceptions &#8211; see article<\/em><\/span>).<\/li>\n<\/ul>\n<p>If you&#8217;ve gone through all these steps and applied the key rules, there are only a handful of possible dilemmas you might be facing based on what we&#8217;ve covered so far.<\/p>\n<p>Those dilemmas are:<\/p>\n<ul>\n<li>A <strong>tertiary<\/strong> carbon with a <strong>weak<\/strong> nucleophile\/base: S<sub>N<\/sub>1 vs E1<\/li>\n<li>A <strong>secondary<\/strong> carbon with <strong>strongly basic<\/strong> nucleophile like RO(-) or HO(-): E2 vs S<sub>N<\/sub>2<\/li>\n<li>A <strong>primary<\/strong> alkyl halide with a <strong>strong<\/strong>, <strong>bulky\u00a0<\/strong>base like\u00a0 <em>t<\/em>-butoxide (<em>t<\/em>-BuO<sup>\u2013 <\/sup>).<\/li>\n<\/ul>\n<p>Once you&#8217;ve looked at those factors, the next factor to evaluate is the <strong>temperature<\/strong>.<\/p>\n<ul>\n<li>The key point of this article is that if\u00a0<strong>heat <\/strong>is indicated,\u00a0it&#8217;s almost certainly <strong>elimination<\/strong>, not substitution, because\u00a0<strong>heat\u00a0<\/strong>favors elimination reactions. [<span style=\"color: #993366;\"><a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2012\/09\/10\/elimination-reactions-are-favored-by-heat\/\"><em>See post: Elimination Reactions Are Favored By Heat<\/em><\/a><\/span>]<\/li>\n<\/ul>\n<h2><a id=\"two\"><\/a>2. Evaluating S<sub>N<\/sub>1 vs E1 : The Role of Heat<\/h2>\n<p>Alright. Let&#8217;s dig into our first case.<\/p>\n<p>Say we have a <strong>tertiary<\/strong> alkyl halide with a weak (neutral) base<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-35799\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/11\/1-examples-of-alkyl-halides-reacting-with-tertiary-alkyl-halides-contrast-room-temperature-versus-heat.gif\" alt=\"-examples of alkyl halides reacting with tertiary alkyl halides - contrast room temperature versus heat\" width=\"640\" height=\"477\" \/><\/a><\/p>\n<ul>\n<li>You should already have ruled out S<sub>N<\/sub>2, due to steric hindrance [<span style=\"color: #993366;\"><em>See article: <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2012\/07\/04\/the-sn2-mechanism\/\">The S<sub>N<\/sub>2 mechanism<\/a><\/em><\/span>]<\/li>\n<li>We have a <strong>weak base<\/strong>, which generally rules out E2.<\/li>\n<\/ul>\n<p>That leaves us with two solid possibilities. S<sub>N<\/sub>1 or E1.<\/p>\n<p><strong>In practice<\/strong>, these reactions generally give a <strong>mixture<\/strong> of substitution (S<sub>N<\/sub>1) and elimination (E1) products.<\/p>\n<p>That being said:<\/p>\n<ul>\n<li>Lower temperatures (e.g. room temperature, 25 \u00b0C) tend to provide mostly S<sub>N<\/sub>1 products.<\/li>\n<li>Higher temperatures (&#8220;heat&#8221;)\u00a0 tend to provide mostly E1 products.<\/li>\n<\/ul>\n<p><img decoding=\"async\" class=\"alignnone wp-image-35800\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/11\/2-generally-lower-temperatures-favor-substitution-sn1-and-higher-temperatures-favor-elimination-e1.gif\" alt=\"generally lower temperatures favor substitution - sn1 - and higher temperatures favor elimination - e1\" width=\"640\" height=\"444\" \/><\/a><\/p>\n<p><em><span style=\"color: #800080;\">In the lab, there is lots of variation, but invariably, higher temperatures result in more eli<span style=\"color: #993366;\">mination. For some real-life results, see<\/span><\/span> <span style=\"color: #ff0000;\"><a href=\"#noteone\">Note 1<\/a>.<\/span>\u00a0(<a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/09\/10\/elimination-reactions-are-favored-by-heat\/\">See article: Elimination Reactions Are Favored By Heat<\/a>)<\/em><\/p>\n<p>Let&#8217;s look at some representative quizzes:<\/p>\n<p><div class=\"wq-quiz-wrapper\" data-id=\"35789\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35789\"] {\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=\"35789\"] {\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=\"35789\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35789\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35789 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35789\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-zoa4f\" data-id=\"zoa4f\">\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\/2630-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\/2630-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 --><br \/>\n<div class=\"wq-quiz-wrapper\" data-id=\"35790\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35790\"] {\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=\"35790\"] {\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=\"35790\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35790\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35790 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35790\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-4brvm\" data-id=\"4brvm\">\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\/2631-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\/2631-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 --><br \/>\n<div class=\"wq-quiz-wrapper\" data-id=\"35791\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35791\"] {\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=\"35791\"] {\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=\"35791\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35791\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35791 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35791\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-3jzp2\" data-id=\"3jzp2\">\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\/2632-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\/2632-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 --><br \/>\n<div class=\"wq-quiz-wrapper\" data-id=\"35792\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35792\"] {\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=\"35792\"] {\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=\"35792\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35792\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35792 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35792\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-5hfkk\" data-id=\"5hfkk\">\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\/2633-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\/2633-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 --><\/p>\n<h2><a id=\"three\"><\/a>3. S<sub>N<\/sub>2 vs E2 &#8211; Secondary Alkyl Halides<\/h2>\n<p>Another dilemma faces us when we encounter a <strong>secondary <\/strong>alkyl halide with a <strong>strong base<\/strong> such as an\u00a0alkoxide (e.g. sodium methoxide, NaOCH<sub>3<\/sub> or potassium ethoxide, KOCH<sub>2<\/sub>CH<sub>3<\/sub> ) or hydroxide (HO<sup>\u2013\u00a0<\/sup>) ion.<\/p>\n<ul>\n<li>The charged nucleophile\/base generally rules out E1 and S<sub>N<\/sub>1<\/li>\n<li>An alkoxide (conjugate base of an alcohol, pK<sub>a<\/sub> 16-18)\u00a0<strong>is\u00a0<\/strong>strong enough to perform elimination through the E2 pathway.<\/li>\n<li>However, a secondary carbon is not sterically hindered enough to <em>completely<\/em> rule out S<sub>N<\/sub>2<\/li>\n<\/ul>\n<p>So our choices at this point are either E2 or S<sub>N<\/sub>2 :<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35801\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/11\/7-for-a-secondary-alkyl-halide-with-strong-base-and-heat-elimination-e2-will-be-favored-over-sn2.gif\" alt=\"-for a secondary alkyl halide with strong base and heat elimination e2 will be favored over sn2\" width=\"640\" height=\"384\" \/><\/a><\/p>\n<ul>\n<li>If\u00a0<strong>heat<\/strong> is applied, then the major product is almost certainly\u00a0<strong>E2\u00a0<\/strong>since elimination reactions are favored by heat.<\/li>\n<li>Absence of heat it does not <em>necessarily<\/em> imply S<sub>N<\/sub>2. <em>But it might. Ask your instructor, because answers vary.\u00a0<\/em><\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35802\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/11\/8-sn2-versus-e2-on-a-secondary-alkyl-halide-with-strong-base-ask-instructor-about-sn2.gif\" alt=\"sn2 versus e2 on a secondary alkyl halide with strong base - ask instructor about sn2\" width=\"640\" height=\"365\" \/><\/a><\/p>\n<p><span style=\"color: #993366;\"><em>For some laboratory results with secondary alkyl halides and strongly basic nucleophiles, see<\/em> <\/span>[<a href=\"#notetwo\"><span style=\"color: #ff0000;\">Note 2<\/span><\/a> ]<\/p>\n<p>Here are some relevant quizzes:<\/p>\n<p><div class=\"wq-quiz-wrapper\" data-id=\"35793\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35793\"] {\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=\"35793\"] {\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=\"35793\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35793\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35793 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35793\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-rrlq7\" data-id=\"rrlq7\">\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\/2634-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\/2634-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 --><br \/>\n<div class=\"wq-quiz-wrapper\" data-id=\"35794\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35794\"] {\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=\"35794\"] {\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=\"35794\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35794\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35794 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35794\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-t4qm0\" data-id=\"t4qm0\">\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\/2635-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\/2635-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 --><br \/>\n<div class=\"wq-quiz-wrapper\" data-id=\"35795\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35795\"] {\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=\"35795\"] {\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=\"35795\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35795\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35795 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35795\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-rzei7\" data-id=\"rzei7\">\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\/2636-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\/2636-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 --><br \/>\n<div class=\"wq-quiz-wrapper\" data-id=\"35796\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35796\"] {\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=\"35796\"] {\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=\"35796\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35796\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35796 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35796\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-cdfto\" data-id=\"cdfto\">\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\/2637-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\/2637-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 --><\/p>\n<h2><a id=\"four\"><\/a>4. S<sub>N<\/sub>2 vs E2 &#8211; Primary Alkyl Halides<\/h2>\n<p>Another S<sub>N<\/sub>2 vs E2 dilemma is presented by a <strong>primary<\/strong> alkyl halide with a\u00a0<strong>bulky strong base\u00a0<\/strong>like KO<em>t-<\/em>Bu in the presence of <strong>heat<\/strong>.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35803\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/11\/13-primary-alkyl-halides-with-bulky-bases-and-heat-can-often-give-elimination-E2-products.gif\" alt=\"primary alkyl halides with bulky bases and heat can often give elimination E2 products\" width=\"640\" height=\"312\" \/><\/a><\/p>\n<ul>\n<li>It can&#8217;t be S<sub>N<\/sub>1\/E1 (primary)<\/li>\n<li>It is\u00a0<strong>likely<\/strong> S<sub>N<\/sub>2 but the bulky base <strong>and<\/strong> heat means that E2 is also a possibility<\/li>\n<\/ul>\n<p>This is another situation where there is variation between different instructors. I&#8217;d suggest asking for clarity from your instructor on this specific question, because answers can vary.<\/p>\n<p>Also be on the lookout for additional factors that may tip the scales away from S<sub>N<\/sub>2. For example,\u00a0 the presence of another alkyl group on the carbon adjacent to the primary alkyl halide will increase steric hindrance on the primary alkyl halide. Since the rate of the S<sub>N<\/sub>2 reaction is very sensitive to steric hindrance, this will make <strong>elimination<\/strong> more likely, relative to substitution.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35804\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/11\/14-the-presence-of-additional-alkyl-groups-on-the-beta-carbon-adjacent-to-the-leaving-group-will-direct-the-reaction-toward-E2-versus-SN2.gif\" alt=\"the presence of additional alkyl groups on the beta carbon adjacent to the leaving group will direct the reaction toward E2 versus SN2\" width=\"640\" height=\"237\" \/><\/a><\/p>\n<p>In the <strong>absence<\/strong> of heat,\u00a0 reactions of primary alkyl halides with\u00a0<em>t<\/em>-butoxide ions will generally be S<sub>N<\/sub>2.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35797\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35797\"] {\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=\"35797\"] {\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=\"35797\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35797\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35797 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35797\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-mf12r\" data-id=\"mf12r\">\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\/2638-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\/2638-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=\"five\"><\/a>5. Heat and the S<sub>N<\/sub>1: Watch Out For Rearrangements<\/h2>\n<p>Although up to this point I&#8217;ve been suggesting a near-Pavlovian relationship between seing &#8220;heat&#8221; and thinking &#8220;elimination&#8221;, it&#8217;s worth putting up a final set of examples where heat is <em>less<\/em> likely to result in elimination.<\/p>\n<p>Secondary alkyl halides\u00a0<em>can<\/em> participate in substitution reactions via the S<sub>N<\/sub>1 pathway, but these reactions are generally quite slow. To happen at any kind of a practical rate, they generally require a kick in the pants in the form of added\u00a0<strong>heat<\/strong>.<\/p>\n<p>Secondary alkyl halides in the presence of poor nucleophiles (like H<sub>2<\/sub>O and alcohols) also provide an opportunity for your instructor to test you on <strong>rearrangement<\/strong> reactions such as hydride shifts and alkyl shifts. (<span style=\"color: #993366;\"><em>See article: <a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/08\/15\/rearrangement-reactions-1-hydride-shifts\/\">Rearrangement reactions with hydride shifts<\/a><\/em><\/span>)<\/p>\n<p>So in these cases (i.e. secondary alkyl halide with poor nucleophile\/base)<strong> it&#8217;s advisable look at the added &#8220;heat&#8221; as making rearrangement more likely, rather than elimination.<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35805\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/11\/16-secondary-alkyl-halides-and-heat-tend-to-give-sn1-reactions-also-with-rearrangements-if-they-are-possible.gif\" alt=\"secondary alkyl halides and heat tend to give sn1 reactions - also with rearrangements if they are possible\" width=\"640\" height=\"446\" \/><\/a><\/p>\n<p>For some results from the lab regarding SN1 vs E1 on secondary alkyl halides, see <a href=\"#notethree\"><span style=\"color: #ff0000;\">Note 3<\/span><\/a>.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35798\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35798\"] {\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=\"35798\"] {\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=\"35798\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35798\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35798 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35798\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-tc9gh\" data-id=\"tc9gh\">\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\/2639-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\/2639-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=\"six\"><\/a>6. Summary<\/h2>\n<p>In case the point hasn&#8217;t been hammered home enough: <em>if you see &#8220;heat&#8221;, think elimination<\/em>.<\/p>\n<p>At the very least, the clear trend is that as temperature is <strong>increased<\/strong>, the <strong>elimination: substitution ratio<\/strong> will <strong>increase<\/strong>.<\/p>\n<p>For exam-preparation purposes, one possible exception to &#8220;heat = elimination&#8221; is the case of <strong>secondary<\/strong> alkyl halides in the presence of <strong>poor<\/strong> nucleophiles such as alcohols or H<sub>2<\/sub>O. In this case, heat provides the activation energy necessary for the leaving group to leave, forming a secondary carbocation (which may then undergo a subsequent elimination reaction, depending on structure).<\/p>\n<p>In the next article, we&#8217;ll cover the last important variable in S<sub>N<\/sub>1\/S<sub>N<\/sub>2\/E1\/E2 &#8211; the <strong>solvent<\/strong>. [<span style=\"color: #800080;\"><em>See article: <a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/12\/04\/deciding-sn1sn2e1e2-the-solvent\/\">Deciding SN1\/SN2\/E1\/E1 &#8211; The Solvent<\/a><\/em><\/span>)<\/p>\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\/2012\/12\/04\/deciding-sn1sn2e1e2-the-solvent\/\" class=\"\"><span>Deciding SN1\/SN2\/E1\/E2 (3) \u2013 The Solvent<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2023\/01\/18\/where-will-substitution-elimination-reactions-occur\/\" class=\"\"><span>Identifying Where Substitution and Elimination Reactions Happen<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/07\/13\/the-sn1-mechanism\/\" class=\"\"><span>The SN1 Mechanism<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/09\/19\/the-e1-reaction\/\" class=\"\"><span>The E1 Reaction<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/11\/08\/comparing-the-e1-and-sn1-reactions\/\" class=\"\"><span>Comparing the E1 vs SN1 Reactions<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/09\/10\/elimination-reactions-are-favored-by-heat\/\" class=\"\"><span>Elimination Reactions Are Favored By Heat<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/11\/21\/deciding-sn1sn2e1e2-1-the-substrate\/\" class=\"\"><span>Deciding SN1\/SN2\/E1\/E2 (1) \u2013 The Substrate<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/11\/30\/deciding-sn1sn2e1e2-2-the-nucleophilebase\/\" class=\"\"><span>Deciding SN1\/SN2\/E1\/E2 (2) \u2013 The Nucleophile\/Base<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/organic-chemistry-practice-problems\/sn1-sn2-e1-e2-practice-problems\/\" class=\"\"><span>SN1 SN2 E1 E2 Practice Problems (MOC Membership)<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2012\/08\/15\/rearrangement-reactions-1-hydride-shifts\/\" class=\"\"><span>Rearrangement Reactions (1) \u2013 Hydride Shifts<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/reaction-guide\/mitsunobu-reaction\/\" class=\"\"><span>Mitsunobu Reaction<\/span><\/a><\/li><\/ul><\/div>\n<p><strong><a id=\"noteone\"><\/a>Note 1.\u00a0<\/strong>The trend of increasing heat resulting in increased elimination products is clear. However it isn&#8217;t always as dramatic as it is in the first example.<\/p>\n<p>Here are some examples from an early paper <span style=\"color: #993366;\"><em>(<\/em><\/span><a href=\"https:\/\/pubs.rsc.org\/en\/Content\/ArticleLanding\/1948\/JR\/JR9480002049\"><span style=\"color: #993366;\"><em>J. Chem. Soc.\u00a0<strong>1948<\/strong>, p. 2049)<\/em><\/span><\/a> that show a more modest relationship between temperature and heat.<\/p>\n<p>First example is with\u00a0<em>t<\/em>-butyl chloride with ethanol and water as solvent:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35841\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/F1-Hughes-sn1-vs-e1-example-.gif\" alt=\"Hughes sn1 vs e1 example\" width=\"640\" height=\"347\" \/><\/a><\/p>\n<p>In the real world, adding heat is <strong>not<\/strong> like flipping a switch that suddenly changes the reaction from one major product to another.\u00a0 Going from 17% elimination at room temperature to 36% elimination at 65\u00b0C is\u00a0 a pretty modest change.<\/p>\n<p>This is why S<sub>N<\/sub>1\/E1 reactions don&#8217;t tend to get used that much in modern organic chemistry &#8211; we get\u00a0<strong>mixtures<\/strong>, and mixtures take time to separate. A better use of our time is employing reactions that will give one dominant product (the E2 would be better for making the alkene here, for instance).<\/p>\n<p>In the same article the authors ran a similar reaction with\u00a0<em>t<\/em>-butyl bromide in 100% ethanol as solvent and varied the heat. The ratio of S<sub>N<\/sub>1: E1 went from 81:19 at 25\u00b0C to 72:28 at 55\u00b0C. <a href=\"\" class=\"custom-tooltip\" data-image=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/F2-hughes-ingold-example-of-sn1-vs-e1-reaction-tert-alkyl-bromide.gif\" data-link=\"\" data-title=\"\" data-text=\"\">Hover here to see this example <\/a> or click this <a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/F2-hughes-ingold-example-of-sn1-vs-e1-reaction-tert-alkyl-bromide.gif\">link<\/a>.<\/p>\n<p>Another reaction reported in the same paper was 2-chloro-2-methylbutane in 80% ethanol\/water. At 25\u00b0C the S<sub>N<\/sub>1:E1 ratio was 67:33, which changed to 60:40 at 50\u00b0C.\u00a0<a href=\"\" class=\"custom-tooltip\" data-image=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/F3-Hughes-1948-alkyl-bromide-sn1-vs-e1-comparison-with-increasing-heat.gif\" data-link=\"\" data-title=\"\" data-text=\"\">Hover here to see this example <\/a> or click this <a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/F3-Hughes-1948-alkyl-bromide-sn1-vs-e1-comparison-with-increasing-heat.gif\">link<\/a>.<\/p>\n<p><strong><a id=\"notetwo\"><\/a>Note 2.\u00a0<\/strong>Despite how important it might seem from the perspective of someone learning organic chemistry for the first time, there actually aren&#8217;t a huge number of examples of S<sub>N<\/sub>2 reactions actually working well between strong bases and secondary alkyl halides.<\/p>\n<p>Maybe the best example is between isopropyl bromide (a.k.a. 2-bromopropane) and sodium ethoxide. In this case, the S<sub>N<\/sub>2 product is produced in 42% yield. This might seem OK at first, until we note that the major product is E2. With heating, the S<sub>N<\/sub>2:E2 ratio decreases even more.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35858\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2012\/12\/F4-sn2-vs-e2-sodium-ethoxide-isopropyl-bronide-hughes-j-chem-soc-1948.gif\" alt=\"sn2 vs e2 sodium ethoxide isopropyl bronide hughes j chem soc 1948\" width=\"640\" height=\"378\" \/><\/a><\/p>\n<p>Things get even worse for S<sub>N<\/sub>2 once an extra alkyl group is added adjacent to the secondary carbon. For isobutyl bromide reacting with NaOEt in ethanol, the S<sub>N<\/sub>2:E2 ratio is 18:82 at 25\u00b0C and 9:91 at 80\u00b0C.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35859\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2012\/12\/F5-sn2-vs-e2-sodium-ethoxide-with-2-bromobutane-chloride-dhar-hughes-ingold-j-chem-soc-1948-2058.gif\" alt=\"-sn2 vs e2 sodium ethoxide with 2-bromobutane chloride dhar hughes ingold j chem soc 1948 2058\" width=\"640\" height=\"402\" \/><\/a><\/p>\n<p>We&#8217;ll have more to say about the S<sub>N<\/sub>2 reaction of secondary alkyl halides with strongly basic nucleophiles in the next article, when we consider\u00a0<strong>solvent<\/strong>.<\/p>\n<p><strong><a id=\"notethree\"><\/a>Note 3.<\/strong> What about <strong>secondary<\/strong> alkyl halides with a\u00a0<strong>poor\u00a0<\/strong>nucleophile\/base? What happens whcn this reaction mixture is heated? Does E1 dominate?<\/p>\n<p>No. One study [<a href=\"https:\/\/doi.org\/10.1039\/JR9480002058\">Ref<\/a>] heated a series of secondary alkyl halides in ethanol at 80\u00b0C. The resulting products were mostly <strong>substitution<\/strong>, with a small amount of elimination (5-15% depending on structure &#8211; the more hindered the secondary alkyl halide, the more elimination took place).<\/p>\n<p><strong><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35936\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2012\/12\/F6-Substitution-reactions-with-heat-secondary-alkyl-halides-treated-with-ethanol-and-heat-give-mostly-substitution-products.gif\" alt=\"Substitution reactions with heat - secondary alkyl halides treated with ethanol and heat give mostly substitution products\" width=\"640\" height=\"434\" \/><\/a><\/strong><\/p>\n<p>Since ethanol is a weak base and not really capable of deprotonation through E2, it was proposed that elimination mostly occurred through an E1 pathway (i.e. carbocation formation, followed by deprotonation to give the alkene).<\/p>\n<p>The substitution products can arise through both S<sub>N<\/sub>2 (direct attack by the solvent) or S<sub>N<\/sub>1 (loss of the leaving group followed by attack of solvent).<\/p>\n<p>At least in the simple cases studied, the major pathway is S<sub>N<\/sub>2.<\/p>\n<p>(Another <a href=\"https:\/\/archive.org\/details\/solvolyticdispla00stre\">unpublished<\/a> study subjected optically active 2-octyl tosylate to heating in ethanol and found the resulting ether (2-ethoxyoctane) to have 81% inversion of configuration. So S<sub>N<\/sub>2 really does seem to be dominant, at least in fairly simple cases.)<\/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\/2662-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\/3574-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\/3575-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\/3576-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\/3577-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>A general, but quite technical, overview of the SN1\/SN2\/E1\/E2 landscape is given in <a href=\"https:\/\/archive.org\/details\/solvolyticdispla00stre\">Solvolytic Displacement Reactions<\/a> by Andrew Streitweiser. It is a useful review of the fragmented early literature on S<sub>N<\/sub>1\/S<sub>N<\/sub>2\/E1\/E2 that includes many tables still found in organic chemistry textbooks today.<\/p>\n<p>Prof. Streitweiser also wrote a popular textbook for introductory organic chemistry in 1976, &#8220;<a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ed054pA294.2\">Introduction To Organic Chemistry<\/a>&#8220;,\u00a0 that went through multiple editions. The section on substitution reactions contains tables of relative rates and yields of various reactions that are also found in his earlier review.<\/p>\n<p>I&#8217;m not sure if it&#8217;s completely fair to lay the current emphasis on S<sub>N<\/sub>1\/S<sub>N<\/sub>2\/E1\/E2 reactions in introductory texts at the feet of Prof. Streitweiser, but there is no question his textbook has had a strong influence on it.<\/p>\n<ol>\n<li><strong>421. Mechanism of elimination reactions. Part XI. Kinetics of olefin elimination from tert.-butyl and tert.-amyl bromides in acidic and alkalinc alcoholic media<br \/>\n<\/strong>M. L. Dhar, E. D. Hughes, C. K. Ingold<br \/>\n<em>J. Chem. Soc.<\/em>, <strong>1948<\/strong>, 2065<br \/>\n<strong>DOI: <a href=\"https:\/\/doi.org\/10.1039\/JR9480002065\">10.1039\/JR9480002065<\/a><br \/>\n<\/strong>Among other things, this is a study of SN1 vs E1 at room temperature (25\u00b0C). At 25\u00b0C in ethanol, <em>t<\/em>-butyl bromide gives 81% substitution (SN1) and 19% elimination (E1) cor. <em>t<\/em>-amyl bromide (2-bromo-2-methylbutane) gives 64% SN1 and 36% E1. The rate constants for each of these reactions are also measured (Table VI).<\/li>\n<li><strong><strong>418. Mechanism of elimination reactions. Part VIII. Temperature effects on rates and product-proportions in uni- and bi-molecular substitution and elimination reactions of alkyl halides and sulphonium salts in hydroxylic solvents<br \/>\n<\/strong><\/strong>K. A. Cooper,\u00a0 E. D. Hughes, C. K. Ingold, B. J. MacNulty<br \/>\n<i><strong>J. Chem. Soc.<\/strong><\/i>, 1948, 2049-2054<br \/>\n<strong><strong>DOI: <a href=\"https:\/\/doi.org\/10.1039\/JR9480002049\">10.1039\/JR9480002049<\/a><br \/>\n<\/strong><\/strong>Study of the effect of increasing temperature on SN1 vs. E1 and SN2 vs. E2. In each case it is found that heat increases the proportion of elimination products. For SN2 and E2 they have this to say:<br \/>\n<em>&#8220;For any given pair of simultaneous bimolecular processes, the elimination has, in each of the investigated cases, an Arrhenius energy of activation which lies higher than that of the accompanying substitution by 1-2 kcals\/mol. <strong>The elimination thus has always the larger temperature coefficient, so that a rise of temperature increases the proportions in which olefin is formed<\/strong>.&#8221;\u00a0<\/em>For SN2 vs. E2 they measure the pre-exponential constant for the Arrhenius equation as well as the energies of activation. The pre-exponential constants for the elimination reactions are higher in each case.<br \/>\nFor SN1 vs E1, the rate determining step is identical for both\u00a0 (loss of the leaving group).<\/li>\n<li><strong><strong>420. Mechanism of elimination reactions. Part X. Kinetics of olefin elimination from isopropyl, sec.-butyl, 2-n-amyl, and 3-n-amyl bromides in acidic and alkaline alcoholic media<br \/>\n<\/strong><\/strong>M. L. Dhar, E. D. Hughes, C. K. Ingold<br \/>\n<em>J. Chem. Soc.\u00a0<\/em><strong>1948<\/strong>. 2058-2065<br \/>\n<strong>DOI: <a href=\"https:\/\/doi.org\/10.1039\/JR9480002058\">10.1039\/JR9480002058<\/a><br \/>\n<\/strong>Intereresting result from this study is the relationship between heat and substitution\/elimination products. Table I in this paper shows that solvolysis of 2-bromobutane with 1 M NaOEt in ethanol gives 82% yield of alkene at 25 \u00b0C, but similar solvolysis at 80 \u00b0C gives 91.4% yield of alkene.<\/li>\n<li><strong>Steric Effects in Elimination Reactions. IX. The Effect of the Steric Requirements of the Leaving Group on the Direction of Bimolecular Elimination in 2-Pentyl Derivatives<br \/>\n<\/strong>Herbert C. Brown and Owen H. Wheeler<strong><br \/>\n<\/strong><em>Journal of the American Chemical Society<\/em><strong>\u00a01956,\u00a0<\/strong><em>78<\/em>\u00a0(10), 2199-2202<strong><br \/>\nDOI:\u00a0<\/strong><a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/ja01591a049\">1021\/ja01591a049<\/a><br \/>\nClassic study on the proportion of alkenes formed through elimination of 2-bromopentane (and similar substrates) with\u00a0<em>t<\/em>-butoxide bases. The major product is always the least substituted alkene (non-Zaitsev alkene).<\/li>\n<li><strong>The Hydrolysis of Tertiary Aliphatic Halides &#8211; I<\/strong><br \/>\nH. Milton Woodburn and F. C. Whitmore<br \/>\n<em>J. Am. Chem. Soc.\u00a0<\/em><strong>1934<\/strong>,\u00a0<em>56<\/em>, 1394<br \/>\n<strong>DOI: <a href=\"https:\/\/pubs.acs.org\/doi\/pdf\/10.1021\/ja01321a055\">10.1021\/ja01321a055<\/a><br \/>\n<\/strong>Hard to find clear literature examples where heat = E1 and no heat = S<sub>N<\/sub>1, but this set from 1934 on the reaction of <em>t<\/em>-amyl halides is fairly straightforward. Conducting the hydrolysis of\u00a0<em>t<\/em>-amyl bromide in the cold gives about 2:1 alcohol : alkene, whereas performing the same reaction under reflux gives exclusively elimination. \u00a0Would like to see this reproduced under more modern conditions and quantified more thoroughly. Note that slight variations in structure (e.g. swapping t-Bu for t-Am, swapping Cl for Br, changing solvents) also has a significant effect on yields\/ratios.<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>SN1 vs E1, and SN2 vs. E2:\u00a0 The Role Of Heat This article assumes you understand the mechanisms of the SN1\/SN2\/E1 and E2 reactions. For <\/p>\n","protected":false},"author":1,"featured_media":35840,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1417],"tags":[472,473,201,868,502,271,279],"post_folder":[],"class_list":["post-6849","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-sn1sn2e1e2","tag-e1","tag-e2","tag-elimination","tag-heat","tag-sn1","tag-sn2","tag-substitution"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>SN1 vs E1 and SN2 vs E2 : The Temperature<\/title>\n<meta name=\"description\" content=\"SN1\/SN2\/E1\/E2 Decision: Temperature. Once a carbocation has formed, how to choose between an E1 and an SN1 pathway? 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