{"id":11001,"date":"2017-09-26T12:51:38","date_gmt":"2017-09-26T16:51:38","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=11001"},"modified":"2026-04-18T06:37:53","modified_gmt":"2026-04-18T11:37:53","slug":"activating-and-deactivating-groups-in-electrophilic-aromatic-substitution","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2017\/09\/26\/activating-and-deactivating-groups-in-electrophilic-aromatic-substitution\/","title":{"rendered":"Activating and Deactivating Groups In Electrophilic Aromatic Substitution"},"content":{"rendered":"<p><strong>Activating and Deactivating Groups in Electrophilic Aromatic Substitution<\/strong><\/p>\n<ul>\n<li>The rate of electrophilic aromatic substitution (EAS) reactions is greatly affected by the groups attached to the ring. <strong>The more electron-rich the aromatic ring, the faster the reaction<\/strong><\/li>\n<li>Groups that can donate electron density to the ring make EAS reactions faster.<\/li>\n<li>If a substituent increases the rate of reaction relative to H it is called\u00a0<strong>activating<\/strong>. If it decreases the rate relative to H it is called\u00a0<strong>deactivating.\u00a0<\/strong>(These rates need to be measured by experiment).<\/li>\n<li><strong><span style=\"color: #ff0000;\">Important!<\/span><\/strong> Groups like OR and NR<sub>2<\/sub> that <strong>seem<\/strong> like they should be deactivating because of their electronegativity are actually <strong>activating<\/strong> since they can donate a lone pair of electrons into the ring through resonance.<\/li>\n<\/ul>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-15846\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/0-summary-of-activating-and-deactivating-groups-in-electrophilic-aromatic-substitution-table-activating-groups-increase-rate-relative-to-h.gif\" alt=\"summary of activating and deactivating groups in electrophilic aromatic substitution table activating groups increase rate relative to h\" width=\"630\" height=\"486\" \/><\/p>\n<p>There&#8217;s a lot to this post, so here&#8217;s a quick index:<\/p>\n<p><strong>Table of Contents<\/strong><\/p>\n<ol>\n<li><a href=\"#one\">Activating And Deactivating Groups<\/a><\/li>\n<li><a href=\"#two\">Measuring Reaction Rates Can Provide Insight Into The Mechanism<\/a><\/li>\n<li><a href=\"#three\">&#8220;Activating&#8221; and &#8220;Deactivating&#8221; Groups &#8211; A Definition<\/a><\/li>\n<li><a href=\"#four\">&#8220;Sigma&#8221; (\u03c3) donors and acceptors (otherwise known as &#8220;inductive effects&#8221;)<\/a><\/li>\n<li><a href=\"#five\">Pi ( \u03c0) Donors and Acceptors (often just called &#8220;Resonance&#8221;)<\/a><\/li>\n<li><a href=\"#six\"><span class=\"s1\">Oxygen And Nitrogens Containing Lone Pairs Are Highly Activating When Bonded Directly To The Ring<\/span><\/a><\/li>\n<li><a href=\"#seven\"><span class=\"s1\"><span class=\"s1\">Halogens (F, Cl, Br, I)\u00a0 Are Deactivating<\/span><\/span><\/a><\/li>\n<li><a href=\"#eight\">Pi Acceptor Groups Are Strongly Deactivating<\/a><\/li>\n<li><a href=\"#nine\">A Table of Activating and Deactivating Groups<\/a><\/li>\n<li><a href=\"#ten\">Summary: What Does This Tell Us About The Mechanism Of Electrophilic Aromatic Substitution?<\/a><\/li>\n<li><a href=\"#quizzes\">Quiz Yourself!\u00a0<\/a><\/li>\n<li><a href=\"#notes\">Notes<\/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. Activating And Deactivating Groups<\/strong><\/h2>\n<p>Last post in this series we introduced <a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/07\/11\/electrophilic-aromatic-substitution-introduction\/\">electrophilic aromatic substitution<\/a>. \u00a0Here&#8217;s the general case:<br \/>\n<img decoding=\"async\" class=\"alignnone wp-image-15847\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/1-electrophilic-aromatic-substitution-benzene-plus-electrophile-plus-lewis-acid-gives-substitution.gif\" alt=\"electrophilic aromatic substitution benzene plus electrophile plus lewis acid gives substitution\" width=\"600\" height=\"199\" \/><\/p>\n<p>Why is this a substitution reaction, you ask? Because we&#8217;re forming and breaking a bond on the same carbon. We <strong>form<\/strong> C\u2013E <em>(where &#8220;E&#8221; is a generic term for &#8220;electrophilic atom&#8221;)<\/em> and we <strong>break<\/strong> C\u2013H.<\/p>\n<p><em>[<span style=\"color: #993366;\">As for the specific identity of &#8220;E&#8221;, we mentioned <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2017\/07\/11\/electrophilic-aromatic-substitution-introduction\/\">six key electrophilic aromatic substitution reactions<\/a> in the last post (bromination, chlorination, nitration, sulfonylation, Friedel-Crafts alkylation and Friedel-Crafts acylation) that we&#8217;ll eventually dig into in detail. But not yet.<\/span> ]<\/em><\/p>\n<p>So if that&#8217;s the summary of\u00a0<em>what<\/em> happens, the next obvious question is:\u00a0<em>how<\/em> does it happen?<\/p>\n<p>In other words, what&#8217;s the mechanism?<\/p>\n<hr \/>\n<p><strong>Obligatory pre-mechanism speech:\u00a0<\/strong>You can&#8217;t determine the mechanism of a chemical reaction merely through logical deduction from first principles. \u00a0Sure, you can make guesses &#8211; even good ones! But the ultimate test of a mechanistic hypothesis is how well it fits with experiment, and that typically involves a lot of lab work. What you&#8217;re taught in an introductory course is the tippy-topmost layer of snow on the iceberg. We give you the best answer, and in retrospect it looks obvious.\u00a0What you don&#8217;t see is all the failure, wrong turns, and false hypotheses that happened along the path towards determining the correct mechanism. However, \u00a0the mechanisms of these reactions that you will learn about weren&#8217;t obvious to most of their discoverers, who were among the brightest and best chemists of their time. <em>Remember that.<\/em><\/p>\n<hr \/>\n<h2><strong><a id=\"two\"><\/a>2. Measuring Reaction Rates Can Provide Insight Into The Mechanism<\/strong><\/h2>\n<p>As far as determining mechanisms is concerned, one of the best tools we have in our experimental arsenal is the ability to measure <strong>reaction rates.\u00a0<\/strong><\/p>\n<p>By measuring the effect that slight tweaks in the experimental conditions (e.g. structure of reactant, temperature, solvent) have upon the rate, we can gather useful insights about how a reaction operates &#8220;under the hood&#8221;.<\/p>\n<p>Of the parameters mentioned above, \u00a0changing the substrate (reactant) is probably the most powerful way to probe a mechanism, because it allows you to tune how electron-rich (nucleophilic) or electron-poor (electrophilic) it is.<\/p>\n<p>Let me show you what I mean.<\/p>\n<p>Let&#8217;s arbitrarily pick one electrophilic aromatic substitution reaction: <strong>nitration<\/strong>.<\/p>\n<ul>\n<li>We know that by adding nitric acid and H<sub>2<\/sub>SO<sub>4<\/sub>, \u00a0benzene can undergo nitration to form nitrobenzene (break C-H, form C-NO<sub>2<\/sub>)<\/li>\n<li>We can even measure the rate of this reaction at a given temperature, concentration, and solvent.<\/li>\n<li>Using the exact same experimental conditions we can then measure the rate of the reaction when <a href=\"https:\/\/en.wikipedia.org\/wiki\/Toluene\" target=\"_blank\" rel=\"noopener noreferrer\">toluene <\/a>(methylbenzene, C<sub>6<\/sub>H<sub>5<\/sub>CH<sub>3<\/sub>) is used as the substrate instead of benzene.<\/li>\n<li>The nitration of toluene is\u00a0<strong>23 times faster<\/strong> than it is for benzene. [<a href=\"#refone\">Ref 1<\/a>]<\/li>\n<li>Using the exact same experimental conditions, we can also use trifluoromethylbenzene (C<sub>6<\/sub>H<sub>5<\/sub>CF<sub>3<\/sub>) as the substrate, and measure the reaction rate.<\/li>\n<li>The nitration of trifluoromethylbenzene is\u00a0<strong>40,000\u00a0<\/strong><strong>times slower<\/strong> than it is for benzene (2.5\u00a0\u00d7 10<sup>-5<\/sup>).<\/li>\n<\/ul>\n<p><img decoding=\"async\" class=\"alignnone wp-image-15848\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/2-effect-of-substituents-on-reaction-rate-methyl-is-activating-trifluoromethyl-is-deactivating.gif\" alt=\"effect of substituents on reaction rate methyl is activating trifluoromethyl is deactivating\" width=\"600\" height=\"435\" \/><a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2017\/09\/2-methyl-and-trifluromethyl-e1504805597532.png\"><br \/>\n<\/a><strong>Bottom line:<\/strong> if we swap a hydrogen on benzene for a methyl group, the reaction is faster.\u00a0If we swap a hydrogen for a trifluoromethyl group, the reaction is slower.<\/p>\n<p>This pattern turns out to be general for other electrophilic aromatic substitution reactions as well (chlorination, bromination, Friedel-Crafts, and others).<\/p>\n<h2><strong><a id=\"three\"><\/a>3. &#8220;Activating&#8221; and &#8220;Deactivating&#8221; Groups &#8211; A Definition<\/strong><\/h2>\n<p>Let&#8217;s call a group <strong>activating\u00a0<\/strong>that\u00a0<strong>increases\u00a0the rate of an electrophilic aromatic substitution reaction, relative to hydrogen<\/strong>. As we just saw, CH<sub>3<\/sub> is a perfect example of an activating group; when we substitute a hydrogen on benzene for CH<sub>3<\/sub>, the rate of nitration is increased.<\/p>\n<p>A\u00a0<strong>deactivating group<\/strong>, on the other hand,\u00a0<strong>decreases the rate of an electrophilic aromatic substitution reaction, relative to hydrogen.\u00a0<\/strong>The trifluoromethyl group, CF<sub>3 ,\u00a0<\/sub>drastically decreases the rate of nitration when substituted for a hydrogen on benzene.<\/p>\n<p>This definition is ultimately based on\u00a0<strong>experimental reaction rate data<\/strong>. \u00a0It doesn&#8217;t tell us\u00a0<strong><em>why<\/em>\u00a0<\/strong>each group accelerates or decreases the rate. &#8220;Activating&#8221; and &#8220;deactivating&#8221; just refers to the effect of each substituent on the rate, relative to H.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15849\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/3-definition-of-activating-and-deactivating-groups-in-electrophilic-aromatic-substitution-activating-groups-increase-rate-relative-to-h.gif\" alt=\"definition of activating and deactivating groups in electrophilic aromatic substitution activating groups increase rate relative to h\" width=\"600\" height=\"348\" \/><\/p>\n<p>&nbsp;<\/p>\n<p>OK then. So why might CH<sub>3<\/sub> increase the rate of reaction, and CF<sub>3<\/sub> decrease it?<\/p>\n<h2><a id=\"four\"><\/a>4. &#8220;Sigma&#8221; (\u03c3) donors and acceptors (otherwise known as &#8220;inductive effects&#8221;)<\/h2>\n<p>Let&#8217;s quickly think back to what we know about alkyl groups (such as CH<sub>3<\/sub>) and haloalkyl groups (such as CF<sub>3<\/sub>), and try to address this question.<\/p>\n<p>In CH<sub>3<\/sub>, the carbon atom is more electronegative (2.5) than hydrogen (2.2). This means that the carbon attracts a bit more than an equal share of electron-density from the covalent bond with H, resulting in a partial negative charge (\u03b4<sup>\u2013<\/sup>) on carbon and a partial positive charge (\u03b4<sup>+<\/sup>) on hydrogen. This partial negative charge is then available to be donated to an adjacent atom. Hence, we tend to think of CH<sub>3<\/sub> as an electron-rich species; an <strong>electron<\/strong>&#8211;<strong>donor<\/strong>.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15850\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/4-alkyl-groups-are-generally-eletron-donating-sigma-donors.gif\" alt=\"alkyl groups are generally eletron donating sigma donors\" width=\"450\" height=\"222\" \/><\/p>\n<p>In CF<sub>3<\/sub> the electrons are pulled in the opposite direction. Three highly electronegative (4.0) fluorine atoms pull electron density away from the carbon atom (2.5), resulting in a partial positive charge (\u03b4<sup>+<\/sup>) on carbon. Rather than donate electron density, the carbon tends to\u00a0<em>accept\u00a0<\/em>(pull away) electron density from adjacent atoms (this is the familiar <a href=\"https:\/\/en.wikipedia.org\/wiki\/Inductive_effect\">inductive effect<\/a>) We generally consider CF<sub>3<\/sub> to be an electron-poor species; an<strong> electron-acceptor<\/strong>.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15851\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/5-electronegative-groups-are-deactivating-through-inductive-effect-cf3-is-sigma-acceptor.gif\" alt=\"electronegative groups are deactivating through inductive effect cf3 is sigma acceptor\" width=\"600\" height=\"283\" \/><\/p>\n<p>Since these inductive effects operate solely through <strong>single bonds<\/strong> (&#8220;sigma&#8221;, or \u03c3\u00a0bonds) this behaviour is sometimes called &#8220;sigma donation&#8221; (as for CH<sub>3<\/sub>) or &#8220;sigma accepting&#8221; (for CF<sub>3<\/sub>).<\/p>\n<p>So it seems like a good hypothesis that<\/p>\n<ul>\n<li><strong>activating groups are\u00a0<\/strong><strong>electron-donating (relative to H), and<\/strong><\/li>\n<li><strong style=\"line-height: inherit;\">deactivating groups are electron-withdrawing (relative to H)<br \/>\n<\/strong><\/li>\n<\/ul>\n<h2><strong><a id=\"five\"><\/a>5. Pi ( \u03c0) Donors and Acceptors (otherwise known as &#8220;Resonance&#8221;)<\/strong><\/h2>\n<p>Sigma donation and acceptance helps us to understand the effect of alkyl groups on electrophilic aromatic substitution. \u00a0So what about other functional groups? What effect might, say, a hydroxyl group have on the rate of nitration?<\/p>\n<p>Quiz time. Do you think \u2013OH would be <strong>activating<\/strong> (increase the rate) or <strong>deactivating<\/strong> (decrease the rate) for electrophilic aromatic substitution (such as nitration)? <em>Guessing is OK!\u00a0<\/em><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15852\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/6-trick-question-what-is-effect-of-oh-on-rate-of-electrophilic-aromatic-substitution-relative-to-H-will-oh-be-activating-or-deactivating.gif\" alt=\"trick question what is effect of oh on rate of electrophilic aromatic substitution relative to H - will oh be activating or deactivating\" width=\"600\" height=\"158\" \/><\/p>\n<p>Based on what we just said, it&#8217;s fully understandable if you said, &#8220;deactivating&#8221;. After all, oxygen is highly electronegative (3.4) and through induction, pulls away electron density through the bond. In other words, it&#8217;s a <strong>sigma-acceptor<\/strong>.<\/p>\n<p>The fact is, however, that <strong>OH\u00a0greatly accelerates the rate,\u00a0<\/strong>orders of magnitude\u00a0more than CH<sub>3<\/sub> does.\u00a0In fact I couldn&#8217;t find good rate data comparing OH to CH<sub>3<\/sub> because in the case of -OH, the reaction is what&#8217;s called, &#8220;diffusion controlled&#8221;. That roughly means, &#8220;as soon as the reactant comes in contact with the electrophile, a reaction occurs.&#8221; In other words, the \u2013OH group is\u00a0<strong>highly activating.\u00a0<\/strong><\/p>\n<p>Clearly, something else must be going on here besides the inductive effect of oxygen!<\/p>\n<h2><a id=\"six\"><\/a>6. Oxygen And Nitrogens Containing Lone Pairs Are Highly Activating When Bonded Directly To The Ring<\/h2>\n<p>As we saw in our chapter way back on resonance, hydroxyl groups are excellent <a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/12\/15\/exploring-resonance-pi-donation\/\"><strong>pi donors<\/strong><\/a>. The lone pairs on the oxygen atom can form a pi bond with an adjacent atom containing an available p-orbital.\u00a0<a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2017\/09\/6-pi-donation-e1506363611188.png\"><br \/>\n<\/a><\/p>\n<p>This donation effect (or &#8220;resonance&#8221;) must outweigh electron-withdrawal via inductive effects, otherwise we&#8217;d observe that hydroxyl groups are deactivating.<\/p>\n<p>The same is true for nitrogen groups with lone pairs, such as amines and amides (below).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15853\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/7-oxygen-and-nitrogen-functional-groups-with-lone-pairs-are-activating-since-they-can-be-pi-donors.gif\" alt=\"oxygen and nitrogen functional groups with lone pairs are activating since they can be pi donors\" width=\"630\" height=\"613\" \/><\/p>\n<p><em>[<span style=\"color: #993366;\">One measure of the importance of pi-donation in the activating nature of amines is seen in their behavior under strongly acidic conditions. \u00a0If the nitrogen lone pair is either protonated with strong acid or undergoes a substitution reaction to form NR<sub>3<\/sub>+ , pi-donation is impossible and the group becomes strongly deactivating (see table below).<\/span> ]<\/em><\/p>\n<h2><strong><a id=\"seven\"><\/a>7. Halogens (F, Cl, Br, I)\u00a0 Are Deactivating<\/strong><\/h2>\n<p>Not all groups capable of pi donation are activating groups. For example, halogens (F, Cl, Br, I) tend to be <strong>deactivating<\/strong>. The rates of electrophilic aromatic substitution reactions on fluorobenzene, chlorobenzene, bromobenzene, and iodobenzene are all slower than they are for benzene itself. \u00a0In these cases, inductive effects (&#8220;sigma accepting&#8221;) would appear to have a greater effect on the rate than any pi-donation from the lone pairs. [pi donation &lt; sigma acceptance]. [<a href=\"#reftwo\">Why?<\/a>]<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15854\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/8-halogens-f-cl-br-i-are-deactivating-groups-slow-electrophilic-aromatic-substitution-relative-to-h.gif\" alt=\"halogens f cl br i are deactivating groups slow electrophilic aromatic substitution relative to h\" width=\"600\" height=\"387\" \/><\/p>\n<p><span style=\"color: #993366;\"><em>A good rule of thumb for pi-donation ability is the basicity of the lone pair. Amines tend to be better bases than oxygens, which are far better bases than halogens.\u00a0<\/em><\/span><\/p>\n<p>Alright. What if electrons flow in the opposite direction? Is there an opposite of &#8220;pi donor&#8221; ?<\/p>\n<h2><strong><a id=\"eight\"><\/a>8. Pi Acceptor Groups Are Strongly Deactivating<\/strong><\/h2>\n<p>Yes! As you may already know, the opposite of a &#8220;pi-donor&#8221; is a &#8220;pi acceptor&#8221;. Certain functional groups can accept, rather than donate, a pi bond from the ring, resulting in a new lone pair on a substituent atom. Examples are NO<sub>2<\/sub>, carbonyl groups (C=O), sulfonyl, cyano (CN) among others. These groups are universally <strong>deactivating<\/strong>, slowing the rate of electrophilic aromatic substitution.<\/p>\n<p>In terms of resonance, one can draw a pi bond from the aromatic ring forming a pi bond with the atom bound to the ring, resulting in formation of a new lone pair on an electronegative atom on the substituent. Note how this results in a positive charge on the ring!<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15855\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/9-pi-acceptor-groups-like-no2-so3h-cn-carbonyl-are-strongly-deactivating-pi-acceptors.gif\" alt=\"pi acceptor groups like no2 so3h cn carbonyl are strongly deactivating pi acceptors\" width=\"600\" height=\"404\" \/><\/p>\n<p><strong>So how do we keep all of these factors straight?<\/strong><\/p>\n<p>This is an example of why I say that <a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/01\/19\/what-to-expect-in-organic-chemistry-2\/\">resonance<\/a> is the most important key concept to review for Org 2. In the section on aromatic chemistry it comes back with a vengeance.<\/p>\n<h2><strong><a id=\"nine\"><\/a>9. A Table of Activating and Deactivating Groups<\/strong><\/h2>\n<p>Now seems like the right time to present a big table of activating and deactivating groups. It&#8217;s hard to rank exactly by power since the effect is averaged over several types of reactions.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15856\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/10-table-of-activating-and-deactivating-groups-for-electrophilic-aromatic-substitution-in-approximate-order-of-ability.gif\" alt=\"table of activating and deactivating groups for electrophilic aromatic substitution in approximate order of ability\" width=\"630\" height=\"425\" \/><a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2017\/09\/9-table-of-ability-1-e1506370562198.png\"><br \/>\n<\/a>Oh dear, this looks like a lot to remember. How to keep it all straight?<\/p>\n<p>I would suggest five main &#8220;buckets&#8221;, below:<\/p>\n<ol>\n<li><b>Nitrogen and oxygens with lone pairs\u00a0<\/b>&#8211; amines (NH<sub>2<\/sub>, NHR, NR<sub>2<\/sub>), phenol (OH) and its conjugate base O<sup>\u2013<\/sup>\u00a0 are very strong activating groups due to pi-donation (resonance). Alkoxy, amide, ester groups less strongly activating.<\/li>\n<li><b>Alkyl Groups &#8211;\u00a0<\/b>(with no electron withdrawing groups). Moderately activating through inductive effect.<\/li>\n<li><strong>Halogens<\/strong>\u00a0&#8211; Moderately deactivating. Electron withdrawing (highly electronegative) nature outweighs donation of electron density through a lone pair.<\/li>\n<li><b>Atoms with pi-bonds to electronegative groups\u00a0<\/b>&#8211; \u00a0Strongly deactivating. NO<sub>2<\/sub>, \u00a0CN, SO<sub>3<\/sub>H, CHO, COR, COOH, COOR, CONH<sub>2<\/sub>. All pi-acceptors.<\/li>\n<li><strong>Electron withdrawing groups with no pi bonds or lone pairs &#8211; <\/strong> Strongly deactivating.\u00a0CF<sub>3<\/sub>, CCl<sub>3<\/sub>, and NR<sub>3<\/sub>(+). Pure inductive effect.<\/li>\n<\/ol>\n<p>Once you remember the somewhat counterintuitive fact that O and N-bonded functional groups with lone pairs are activating, and halogens are deactivating, the rest is fairly straightforward.<\/p>\n<p>One final word. Our table of &#8220;activating&#8221; and &#8220;deactivating&#8221; groups turns out to be a little bit like a pK<sub>a<\/sub> table. How? We can evaluate several factors that have an impact on pKa, but the ultimate test of which factor is more important is experimental measurement of an equilibrium constant. Likewise, with activating and deactivating groups, we can identify factors which may or may not make a certain group activating or deactivating, but in the end, its position on the chart comes down to experimental measurements of reaction rates.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"37835\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"37835\"] {\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=\"37835\"] {\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=\"37835\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-37835\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-37835 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"37835\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-kjbn8\" data-id=\"kjbn8\">\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\/2446-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\/2446-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=\"ten\"><\/a>10. Summary: <strong>What Does This Tell Us About The Mechanism Of Electrophilic Aromatic Substitution?<\/strong><\/h2>\n<p>OK. So what does all of this tell us?<\/p>\n<p>Since the rate is so sensitive to whether the group is electron donating or electron withdrawing <em>(&#8220;electronic effects&#8221;, as organic chemists might quickly summarize it)<\/em> it would suggest that <strong>the rate determining step is the formation of a\u00a0fairly unstable electron-poor species<\/strong>, <strong>such as a carbocation<\/strong>.<\/p>\n<p>Recall CH<sub>3<\/sub> and CF<sub>3<\/sub>. You may recall that the order of carbocation stability (tertiary &gt; secondary &gt; primary) is due to the fact that carbocations are <a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/03\/11\/3-factors-that-stabilize-carbocations\/\">stabilized<\/a> by adjacent alkyl groups (such as CH<sub>3<\/sub>), and, conversely, are <a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/03\/21\/three-factors-that-destabilize-carbocations\/\">destabilized<\/a> by adjacent electron withdrawing groups (like CF<sub>3<\/sub>).<\/p>\n<p>Likewise, carbocations are stabilized by adjacent atoms that can donate lone pairs (e.g. O and N) through resonance, and destabilized by pi acceptors such as C=O, NO<sub>2<\/sub>, and so on.<\/p>\n<p>A likely first step would be something like this:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15857\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/11-what-is-mechanism-of-electrophilic-aromatic-substitution-first-step-is-attack-of-pi-bond-on-electrophile-giving-carbocation.gif\" alt=\"what is mechanism of electrophilic aromatic substitution first step is attack of pi bond on electrophile giving carbocation\" width=\"600\" height=\"184\" \/><\/p>\n<p>We&#8217;ll go into the full mechanism of electrophilic aromatic substitution in the next post, but will fill in additional detail in a bonus topic below.<\/p>\n<p><strong>Next Post:<a href=\"https:\/\/www.masterorganicchemistry.com\/2017\/11\/09\/electrophilic-aromatic-substitution-the-mechanism\/\"> Electrophilic Aromatic Substitution: The Mechanism<\/a><\/strong><\/p>\n<hr \/>\n<h2><a id=\"quizzes\"><\/a>Quiz Yourself!<\/h2>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-36214 aligncenter\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2909-Front-Image-Only.png\" alt=\"\" width=\"600\" height=\"451\" \/><\/a><br \/>\n<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<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-36214 aligncenter\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2910-Front-Image-Only.png\" alt=\"\" width=\"600\" height=\"451\" \/><\/a><br \/>\n<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\/0511-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\/3044-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\/3045-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<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\/2017\/11\/09\/electrophilic-aromatic-substitution-the-mechanism\/\" class=\"\"><span>Electrophilic Aromatic Substitution \u2013 The Mechanism<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/03\/05\/why-are-halogens-ortho-para-directors\/\" class=\"\"><span>Why are halogens ortho- para- directors?<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/02\/02\/understanding-ortho-para-meta-directors\/\" class=\"\"><span>Understanding Ortho, Para, and Meta Directors<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/01\/29\/ortho-para-and-meta-directors-in-electrophilic-aromatic-substitution\/\" class=\"\"><span>Ortho-, Para- and Meta- Directors in Electrophilic Aromatic Substitution<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/04\/18\/electrophilic-aromatic-substitutions-1-halogenation\/\" class=\"\"><span>Electrophilic Aromatic Substitutions (1) \u2013 Halogenation of Benzene<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/organic-chemistry-practice-problems\/aromaticity-practice-quizzes\/\" class=\"\"><span>Aromaticity Practice Quizzes (MOC Membership)<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/10\/08\/nitration-baeyer-villiger\/\" class=\"\"><span>More Reactions on the Aromatic Sidechain: Reduction of Nitro Groups and the Baeyer Villiger<\/span><\/a><\/li><\/ul><\/div>\n<p>Possibly a useful reference sheet. Adapted from Ingold&#8217;s &#8220;Structure and Mechanism in Organic Chemistry&#8221;, 2nd ed.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-38902\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2025\/02\/Selected-Relative-Rates-for-Mono-Nitration-of-Benzene-Derivatives-alkyl-groups-moderately-activating-nitro-strongly-deactivating-nr3-strongly-deactivating.gif\" alt=\"Selected Relative Rates for Mono Nitration of Benzene Derivatives alkyl groups moderately activating nitro strongly deactivating nr3 strongly deactivating\" width=\"640\" height=\"650\" \/><\/a><\/p>\n<p><em><strong>1. [Advanced] No deuterium isotope effect is observed in electrophilic aromatic substitution<\/strong><\/em><\/p>\n<p>In electrophilic aromatic substitution a C-H bond is broken. \u00a0One way to probe the mechanisms of reactions that involve C-H bond cleavage is to use deuterium (D) labelling. In reactions where C-H bond breakage is a rate-determining step (e.g. E2 elimination) a C-H bond can break up to 6-7 times faster than a C-D bond. This is called a <a href=\"https:\/\/en.wikipedia.org\/wiki\/Kinetic_isotope_effect\">deuterium isotope effect<\/a> and it is measurable.<\/p>\n<p>Electrophilic aromatic substitution reactions have no significant deuterium isotope effects. [<a href=\"#notethree\">Note<\/a>] This strongly suggests that C-H bond breakage is not the rate determining step.<\/p>\n<p><strong><em>2. Carbocation intermediates have been isolated that strongly support the proposed mechanism<\/em><\/strong><\/p>\n<p>Here&#8217;s a species that&#8217;s been observed when 1,3,5-trimethylbenzene (mesitylene) is treated with ethyl fluoride and boron trifluoride at \u201380\u00b0C <em>(this is a Friedel-Crafts alkylation reaction, by the way). <\/em><\/p>\n<p>The carbocation intermediate (called an &#8220;arenium ion&#8221; or &#8220;Wheland intermediate&#8221; was isolated as a white solid with melting point \u201315\u00b0C, and analyzed by NMR spectroscopy.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-15858\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/F1-extremely-strong-evidence-for-intermediate-carbocation-is-arenium-ion-or-wheland-intermediate-isolated-as-solid-with-melting-point-of-15.gif\" alt=\"extremely strong evidence for intermediate carbocation is arenium ion or wheland intermediate isolated as solid with melting point of -15\" width=\"600\" height=\"273\" \/><a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2017\/09\/11-arenium-ion-e1506443714350.png\"><br \/>\n<\/a>As <a href=\"https:\/\/chemistry.harvard.edu\/people\/eric-jacobsen\">Eric Jacobsen<\/a> might say: &#8220;mechanisms can never be proven, but&#8230;.&#8221; . <em>(this pretty much seals the deal).<\/em> We&#8217;ll go into in more detail in the next post.<\/p>\n<p><a id=\"refone\"><\/a><strong>Note 1. <\/strong>Reference: March, Advanced Organic Chemistry 5th ed, page 692.<\/p>\n<p><a id=\"reftwo\"><\/a><strong>Note 2<\/strong>. Why? Interestingly, fluorine is the most activating of the halogens. The reason is likely that the overlap of the lone pair in the fluorine 2p orbital with the p orbital on carbon is much better (resulting in a stronger pi-bond) than is donation with the 3p (and higher) p orbitals of chlorine, bromine, and iodine.<\/p>\n<p><a id=\"notethree\"><\/a>\u00a0<strong>Note 3. <\/strong>Actually a white lie; some electrophilic aromatic substitution reactions do have <em>very small<\/em> deuterium isotope effects, but we&#8217;re not touching that topic, nosiree.<span style=\"color: #999999;\"> <em>[partitioning effects, see March&#8217;s Advanced Organic Chemistry, 5th ed., p. 679]<\/em><\/span><\/p>\n<hr \/>\n<h2><a id=\"references\"><\/a>(Advanced) References and Further Reading<\/h2>\n<p>As mentioned, this topic is useful for all types of EAS reactions \u2013 Friedel-Crafts alkylation\/acylation, halogenation, nitration, etc.<\/p>\n<ol>\n<li><strong>\u2014The chlorination of anilides. The directing influence of the acylamido-group<br \/>\n<\/strong>Kennedy Joseph Previt\u00e9 Orton and Alan Edwin Bradfield<br \/>\n<em>J. Chem. Soc.<\/em> <strong>1927<\/strong>, 986-997<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.rsc.org\/en\/Content\/ArticleLanding\/JR\/1927\/JR9270000986#!divAbstract\">10.1039\/JR9270000986<\/a><strong><br \/>\n<\/strong>An early paper discussing the <em>ortho\/para<\/em> product distribution obtained by electrophilic chlorination of anilides (generally 65% <em>para<\/em>\/35% <em>ortho<\/em>). Unfortunately this paper does not have data comparing the rate of chlorination to benzene.<\/li>\n<li><strong>Kinetics and mechanism of some electrophilic benzene substitution reactions<br \/>\n<\/strong>Alan E. Bradfield and Brynmor Jones<strong><br \/>\n<\/strong><em> Faraday Soc.<\/em> <strong>1941<\/strong>, <em>37<\/em>, 726-743<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1941\/TF\/TF9413700726#!divAbstract\">10.1039\/TF9413700726<\/a><br \/>\nTable I in this paper contains partial rate factors for nitration of benzene and related compounds. Chlorobenzene and bromobenzene are around 1-3% as reactive as benzene, whereas ethyl benzoate is <em>significantly deactivated <\/em>\u2013 it is around 0.1-0.2% as reactive as benzene! Toluene is 40-50 times as reactive as benzene.<\/li>\n<li><strong> The kinetics of aromatic halogen substitution. Part IX. Relative reactivities of monosubstituted benzenes<br \/>\n<\/strong>P. W. Robertson, P. B. D. de la Mare, and B. E. Swedlund<strong><br \/>\n<\/strong><em>J. Chem. Soc.<\/em> <strong>1953<\/strong>, 782-788<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.rsc.org\/en\/Content\/ArticleLanding\/1953\/JR\/JR9530000782#!divAbstract\">10.1039\/JR9530000782<\/a><br \/>\nPg. 783 in this paper contains data for reaction rates of halogenation of various benzene derivatives. This spans the gamut of extreme activating substituents (N,N-dimethylaniline is <em>10<sup>18<\/sup> times more reactive than benzene<\/em>!) and deactivating substituents (nitrobenzene is 10<sup>-6<\/sup> times less reactive than benzene).<\/li>\n<li><strong> The influence of the methoxyl group in aromatic substitution<br \/>\n<\/strong>P. B. D. de la Mare and C. A. Vernon<strong><br \/>\n<\/strong><em>J. Chem. Soc.<\/em> <strong>1951<\/strong>, 1764-1767<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1951\/JR\/jr9510001764#!divAbstract\">10.1039\/JR9510001764<\/a><br \/>\nThis paper examines the effect of -OMe in electrophilic aromatic substitution (e.g. anisole and related compounds vs. benzene). Overall, anisole is 10<sup>8<\/sup> times more reactive than benzene, and as a result, o\/p selectivity in reactions is very low.<\/li>\n<li><strong>Rates of Bromination of Anisole and Certain Derivatives. Partial Rate Factors for the Bromination Reaction. The Application of the Selectivity Relationship to the Substitution Reactions of Anisole<br \/>\n<\/strong>Leon M. Stock and Herbert C. Brown<strong><br \/>\n<\/strong><em>Journal of the American Chemical Society<\/em><strong> 1960, <\/strong><em>82<\/em> (8), 1942-1947<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja01493a026\">1021\/ja01493a026<\/a><br \/>\nThis paper is a more rigorous study of the bromination of anisole by Nobel Laureate Prof. H. C. Brown. The o\/p selectivity of anisole is actually rather high \u2013 bromination gives 1.6% <em>o<\/em>&#8211; and 98.4% <em>p<\/em>-bromoanisole. The relative reaction of anisole:benzene is also measured to be 1.79 x 10<sup>9<\/sup>:1.00. This paper also shows that s<sup>+<\/sup> values (electrophilic Hammett constants) measured this way are comparable to Hammett values measured through other methods, and that the Hammett values also provide a good measure of how a substituent will effect EAS reactions as well.<\/li>\n<li><strong>\u2014Influence of directing groups on nuclear reactivity in oriented aromatic substitutions. Part II. Nitration of toluene<br \/>\n<\/strong>Christopher Kelk Ingold, Arthur Lapworth, Eugene Rothstein, and Denis Ward<strong><br \/>\n<\/strong><em>J. Chem. Soc.<\/em> <strong>1931<\/strong>, 1959-1982<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1931\/JR\/JR9310001959#!divAbstract\">10.1039\/JR9310001959<\/a><strong><br \/>\n<\/strong>This is the first paper to introduce the term \u2018partial rate factor\u2019 (usually denoted by <em>f<sub>p<\/sub>, f<sub>o<\/sub>, f<sub>m<\/sub><\/em>) to denote the amount by which a specific position on a substituted benzene may be more or less reactive compared to benzene. Table IV shows in this paper that toluene can be anywhere from 1.2 \u2013 10 times more reactive than benzene.<\/li>\n<li><strong>Effects of Alkyl Groups in Electrophilic Additions and Substitutions<br \/>\n<\/strong>COHN, H., HUGHES, E., JONES, M. and PEELING, M. G.<strong><br \/>\n<\/strong><em>Nature <\/em><strong>1952, <\/strong><em>169<\/em>, 291<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/www.nature.com\/articles\/169291a0\">1038\/169291a0<\/a><br \/>\nThis paper has data comparing the nitration of <em>t<\/em>-butylbenzene and toluene. <em>T<\/em>-butylbenzene is much more <em>p<\/em>-directing than toluene (79.5% <em>para<\/em> for t-butylbenzene vs. 40% <em>para<\/em> for toluene), which is likely due to sterics (<em>ortho<\/em> approach is blocked by the bulkier t-butyl group).<\/li>\n<li><strong> The transmission of polar effects through aromatic systems. Part II. The nitration of benzyl derivatives<br \/>\n<\/strong>J. R. Knowles and R. O. C. Norman<strong><br \/>\n<\/strong><em>J. Chem. Soc.<\/em> <strong>1961<\/strong>, 2938-2947<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1961\/jr\/jr9610002938\/unauth#!divAbstract\">10.1039\/JR9610002938<\/a><br \/>\nJ. R. Knowles went on to become a Professor at Harvard, specializing in enzymology. The knowledge of kinetics that one gets from doing physical organic chemistry is applicable in a wide variety of areas! In this paper, Table 2 is interesting, and shows that the empirical reactivity difference between toluene and benzene is 25x, which is what is commonly found in textbooks today. T-butylbenzene is less reactive than toluene, but still 15x more reactive than benzene.<\/li>\n<li><strong> Influence of directing groups on nuclear reactivity in oriented aromatic substitutions. Part IV. Nitration of the halogenobenzenes<\/strong><br \/>\nMarjorie L. Bird and Christopher K. Ingold<br \/>\n<em>J. Chem. Soc.<\/em> <strong>1938<\/strong>, 918<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.rsc.org\/en\/Content\/ArticleLanding\/JR\/1938\/JR9380000918#!divAbstract\">10.1039\/JR9380000918<\/a><br \/>\nTable I in this paper shows that overall, chlorobenzene and bromobenzene are around 2-3% as reactive as benzene towards nitration under a wide variety of conditions.<\/li>\n<li><strong> Some aspects of the nitration of the mononitrotoluenes<br \/>\n<\/strong>J. G. Tillett<br \/>\n<em>J. Chem. Soc.<\/em> <strong>1962<\/strong>, 5142-5148<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1962\/jr\/jr9620005142#!divAbstract\">10.1039\/JR9620005142<\/a><br \/>\nPg. 5148 in this paper shows that in nitrotoluenes, the deactivating nature of nitro wins out over the activating nature of the methyl group. Interestingly, in <em>m<\/em>-nitrotoluene, the <em>meta <\/em>position to the nitro group is less reactive than the other positions, due to resonance effects. Note that these compounds are also precursors to the common explosive TNT!<\/li>\n<li><strong> Substituent effects of positive poles in aromatic substitution. Part I. The nitration of the anilinium ion in 90\u2014100% sulphuric acid<\/strong><br \/>\nMadeline Brickman and J. H. Ridd<br \/>\n<em>J. Chem. Soc.<\/em> <strong>1965<\/strong>, 6845-6851<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1965\/jr\/jr9650006845\/unauth#!divAbstract\">10.1039\/JR9650006845<\/a><\/li>\n<li><strong> Substituent effects of positive poles in aromatic substitution. Part II. The nitration of N-methylated anilinium ions<\/strong><br \/>\nMadeline Brickman, J. H. P. Utley, and J. H. Ridd<br \/>\n<em>J. Chem. Soc.<\/em> <strong>1965<\/strong>, 6851-6857<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1965\/jr\/jr9650006851\/unauth#!divAbstract\">10.1039\/JR9650006851<\/a><br \/>\nIn contrast to aniline, which is very reactive in EAS compared to benzene, the anilinium ion (which is easily formed in acidic media) is deactivated. As the acidity of the medium increases, the amount of <em>meta<\/em> product obtained from nitration of aniline increases, indicating that the reaction is proceeding via the anilinium ion (PhNH<sub>3<\/sub><sup>+<\/sup>). Reaction rates also decrease with increasing acidity, as the amount of free aniline available in the reaction gets lower and lower.<\/li>\n<li><strong>Aromatic substitution. 53. Electrophilic nitration, halogenation, acylation, and alkylation of (.alpha.,.alpha.,.alpha.-trifluoromethoxy)benzene<\/strong><br \/>\nGeorge A. Olah, Takehiko Yamato, Toshihiko Hashimoto, Joseph G. Shih, Nirupam Trivedi, Brij P. Singh, Marc Piteau, and Judith A. Olah<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1987,<\/strong> <em>109<\/em> (12), 3708-3713<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja00246a030\">10.1021\/ja00246a030<\/a><br \/>\nThe -OCF<sub>3<\/sub> substituent is not commonly encountered in undergraduate chemistry courses, but is used in medicinal chemistry. This paper by Nobel Laureate Prof. George A. Olah and his wife Judith, covers the directing effects and reactivity of PhOCF<sub>3<\/sub> in a variety of EAS reactions. Overall, PhOCF<sub>3<\/sub> is around 3-10% as reactive as benzene in EAS (see Tables VI-VIII).<\/li>\n<li><strong>A Quantum Mechanical Investigation of the Orientation of Substituents in Aromatic Molecules<br \/>\n<\/strong>G. W. Wheland<strong><br \/>\n<\/strong><em>Journal of the American Chemical Society<\/em> <strong>1942,<\/strong> <em>64<\/em> (4), 900-908<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja01256a047\">10.1021\/ja01256a047<\/a><br \/>\nThis discusses the structure of the arenium ion that gets formed in EAS reactions, also known as the s-complex or Wheland intermediate, after the author here who first proposed it.<\/li>\n<li><strong>Isolation of the Stable Boron Trifluoride \u2013 Hydrogen Fluoride Complexes of the Methyl-benzenes ; the Onium Salt (or \u03c3-Complex) Structure of the Friedel-Crafts Complexes<br \/>\n<\/strong>OL\u00c1H, G., KUHN, S. &amp; PAVL\u00c1TH, A.<strong><br \/>\n<\/strong><em>Nature<\/em><strong> 1956, <\/strong><em>178<\/em>, 693\u2013694<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/www.nature.com\/articles\/178693b0\">1038\/178693b0<\/a><\/li>\n<li><strong>The Benzotrifluoride\u2013Nitryl Fluoride\u2013Boron Trifluoride Complex<br \/>\n<\/strong>OL\u00c1H, G., NOSZK\u00d3, L. &amp; PAVL\u00c1TH, A.<strong><br \/>\n<\/strong><em>Nature<\/em><strong> 1957, <\/strong><em>179<\/em><strong>, <\/strong>146\u2013147<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/www.nature.com\/articles\/179146b0\">1038\/179146b0<\/a><\/li>\n<li><strong>Isolation of the Stable Boron Trifluoride-ethylfluoride and Boron Trifluoride-formylfluoride Complexes of the Methylbenzenes: Mechanism of the Friedel\u2013Crafts Reactions<br \/>\n<\/strong>OL\u00c1H, G., KUHN, S.<strong><br \/>\n<\/strong><em>Nature<\/em><strong> 1956, <\/strong><em>178<\/em><strong>, <\/strong>1344\u20131345<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/www.nature.com\/articles\/1781344a0\">10.1038\/1781344a0<\/a><br \/>\nThese papers by Nobel Laureate Prof. G. A. Olah describe the isolation and characterization of the intermediate ions (\u2018Wheland intermediates\u2019) from various electrophilic aromatic substitution reactions \u2013 alkylation, nitration, and even protonation (by HBF<sub>4<\/sub>!)<\/li>\n<li><strong>A Quantitative Treatment of Directive Effects in Aromatic Substitution<br \/>\n<\/strong>Leon M. Stock, Herbert C. Brown<strong><br \/>\n<\/strong><em> Phys. Org. Chem.<\/em><strong> 1963, <\/strong><em>1<\/em>, 35-154<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/www.sciencedirect.com\/bookseries\/advances-in-physical-organic-chemistry\/vol\/1\/suppl\/C\">10.1016\/S0065-3160(08)60277-4<\/a><br \/>\nThis is a very comprehensive review for its time, summarizing work on directing effects in EAS (e.g. determining which groups are <em>o\/p-<\/em>directing vs. <em>meta<\/em>-directing, and to what extent they direct\/deactivate).<\/li>\n<li><strong>Stable carbocations. CLXX. Ethylbenzenium ions and the heptaethylbenzenium ion<br \/>\n<\/strong>George A. Olah, Robert J. Spear, Guisseppe Messina, and Phillip W. Westerman<strong><br \/>\n<\/strong><em>Journal of the American Chemical Society<\/em><strong> 1975, <\/strong><em>97<\/em> (14), 4051-4055<strong><br \/>\nDOI: <\/strong>1021\/ja00847a031<br \/>\nThis paper discusses the characterization of benzenium ions, which are intermediates in EAS, and the characterization of the heptaethylbenzenium ion, which is a stable species because it lacks a proton and therefore eliminates with difficulty.<\/li>\n<li><strong>The Anomalous Reactivity of Fluorobenzene in Electrophilic Aromatic Substitution and Related Phenomena<br \/>\n<\/strong>Joel Rosenthal and David I. Schuster<strong><br \/>\n<\/strong><em>Journal of Chemical Education<\/em><strong> 2003, <\/strong><em>80<\/em> (6), 679<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ed080p679\">1021\/ed080p679<\/a><br \/>\nA very interesting paper, suitable for curious undergrads, and discusses something that most practicing organic chemists will know empirically \u2013 fluorobenzene is almost as reactive as benzene in EAS or Friedel-Crafts reactions, which is counterintuitive when one considers electronic effects.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>Activating and Deactivating Groups in Electrophilic Aromatic Substitution The rate of electrophilic aromatic substitution (EAS) reactions is greatly affected by the groups attached to the <\/p>\n","protected":false},"author":1,"featured_media":15846,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1297],"tags":[1274,1275,1276,199,319,1278,305,670,267,1279,1277],"post_folder":[],"class_list":["post-11001","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-aromatic-reactions","tag-activating-group","tag-deactivating-group","tag-deuterium-isotope","tag-electronegativity","tag-electrophilic-aromatic-substitution","tag-pi-acceptor","tag-pi-donation","tag-reaction-rate","tag-resonance","tag-sigma-acceptor","tag-sigma-donation"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Activating and Deactivating Groups In Electrophilic Aromatic Substitution<\/title>\n<meta name=\"description\" content=\"What are activating and deactivating groups in organic chemistry? 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