{"id":2120,"date":"2010-07-01T18:19:52","date_gmt":"2010-07-01T17:19:52","guid":{"rendered":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120"},"modified":"2011-07-07T06:05:08","modified_gmt":"2011-07-07T06:05:08","slug":"the-mysteries-of-stereoinduction","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120","title":{"rendered":"The mysteries of stereoinduction."},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"2120\">\n<p>Stereo-induction is, lets face it, a <a href=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/talks\/hofmann\/\" target=\"_blank\">subtle phenomenon<\/a>. The ratio of two stereoisomers formed in a reaction can be detected very accurately by experiment, and when converted to a free energy difference using \u0394G = -RT Ln K, this can amount to quite a small value (between 0.5 &#8211; 1.5 kcal\/mol). Can modelling reproduce effects originating from such small energy differences? Well one system that has been argued about now for several decades is shown below as <strong>1<\/strong>.<\/p>\n<div id=\"attachment_2121\" style=\"width: 411px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene.jpg\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2121\" class=\"size-full wp-image-2121\" title=\"Stereoinduction: syn or anti?\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene.jpg\" alt=\"\" width=\"401\" height=\"148\" \/><\/a><p id=\"caption-attachment-2121\" class=\"wp-caption-text\">Norbornene systems<\/p><\/div>\n<p><a href=\"http:\/\/dx.doi.org\/10.1039\/C39920000998\" target=\"_blank\">Way back in 1992<\/a>, we thought that the explanation for attack by an electrophile on the alkene from the <em>syn<\/em> face was electrostatic (although it did depend on the nature of the electropile; thus we concluded that attack by Hg(OH)<sub>2<\/sub> was electrostatic, but by BH<sub>3<\/sub> was orbital controlled). Recently, a different explanation has emerged, relating to how the fundamental normal vibrational modes of the molecule interact with the transition normal mode for the reaction. A <a href=\"http:\/\/dx.doi.org\/10.1038\/nchem.577\" target=\"_blank\">new example of this<\/a>, relating to reaction of the isomeric <strong>2<\/strong> with a peracid has recently been discussed on <a href=\"http:\/\/comporgchem.com\/blog\/?p=977\" target=\"_blank\">Steve Bachrach&#8217;s blog<\/a>. Here, the peroxide of the peracid is thought to act as an electrophile (although one must bear in mind that it does bear two electron lone pairs!). The conclusion was pretty clear cut; the experimental preference for <em>syn<\/em> (92%) over the <em>anti<\/em> isomer (8%, \u0394\u0394G = 1.4 kcal\/mol) was NOT due to electrostatic effects, but due to distorsional asymmetry in the vibrational mode that couples\/forms the transition state mode.<\/p>\n<p>I could not resist revisiting this system. As in 1992, a molecular electrostatic potential was calculated for <strong>2<\/strong>. The method used was wB97XD\/aug-cc-pvdz, and if you want the archive of this calculation to evaluate it yourself, <a href=\"http:\/\/hdl.handle.net\/10042\/to-4996\" target=\"_blank\">see here<\/a>).<\/p>\n<p><div id=\"attachment_2122\" style=\"width: 273px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2122\" class=\"size-full wp-image-2122\" title=\"Electrostatic potential\" onclick=\"jmolInitialize('..\/Jmol\/');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content\/uploads\/2010\/07\/norbornene_0.029.jvxl;isosurface &quot;&quot; translucent;zoom 60;spin 3;');\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene-0.031.jpg\" alt=\"\" width=\"263\" height=\"263\" \/><p id=\"caption-attachment-2122\" class=\"wp-caption-text\">MEP for 2. Click on diagram for 3D.<\/p><\/div>A very clear electrostatic bias for <em>syn<\/em> attack emerges (orange = attractive to a proton=electrophile). This electrostatic picture is not directly related to any distortional asymmetry, although of course both could arise from the same electronic factors. They may indeed be different manifestations of the same underlying nature of the wavefunction. But I would claim here that to make the clear statement that electrostatic effects are <strong>NOT<\/strong> responsible for the discrimination in this reaction is perhaps too simplistic (electrostatic potentials were not reported in the original article). The control experiment is <strong>3<\/strong>, which is known to be far less selective. The calculated electrostatic potential likewise shows much less discrimination.<\/p>\n<p><div id=\"attachment_2136\" style=\"width: 231px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2136\" class=\"size-full wp-image-2136\" title=\"The norbornene with a four-membered ring\" onclick=\"jmolInitialize('..\/Jmol\/');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content\/uploads\/2010\/07\/norbornene4_0.029.jvxl;isosurface &quot;&quot; translucent;zoom 60;spin 3;');\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene4-0.029.jpg\" alt=\"\" width=\"221\" height=\"239\" \/><p id=\"caption-attachment-2136\" class=\"wp-caption-text\">The norbornene with a four-membered ring<\/p><\/div>Is there another take on <strong>2<\/strong>? Well, how about an NBO (natural bond order) analysis? The interaction energy between the filled C1-C2 orbital and the antibonding\u00a0C15-C16 \u03c0* bond is 3.24. This could be regarded as pushing electrons into the anti-periplanar <em>syn<\/em> face of the alkene. The corresponding\u00a0C2-C9\/C15-C16 interaction resulting in an <em>anti<\/em>-preference is less at 2.55 kcal\/mol. This effect arises because the C1-C2 bond (localised as an NBO) is a better donor (E=-17.8eV) than C2-C9 (E=-18.1eV). Because C2 is common to both, it must be the difference between C1 and C9 (i.e. the hybridization of each). Perhaps it&#8217;s an orbital effect after all?<\/p>\n<div id=\"attachment_2124\" style=\"width: 304px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene-0.029.jpg\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2124\" class=\"size-full wp-image-2124\" title=\"Norbornene electrostatic potential\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene-0.029.jpg\" alt=\"\" width=\"294\" height=\"294\" \/><\/a><p id=\"caption-attachment-2124\" class=\"wp-caption-text\">Norbornene electrostatic potential<\/p><\/div>\n<p>I would conclude by saying that it can be ferociously difficult to identify the fundamental origins of stereo-induction. But I leave the argument in the hands of the reader now. What do you think?<\/p>\n<!-- kcite active, but no citations found -->\n<\/div> <!-- kcite-section 2120 -->","protected":false},"excerpt":{"rendered":"<p>Stereo-induction is, lets face it, a subtle phenomenon. The ratio of two stereoisomers formed in a reaction can be detected very accurately by experiment, and when converted to a free energy difference using \u0394G = -RT Ln K, this can amount to quite a small value (between 0.5 &#8211; 1.5 kcal\/mol). Can modelling reproduce effects [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[4],"tags":[575,239,240,238,41,2648,20],"ppma_author":[2661],"class_list":["post-2120","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-chiroptical","tag-energy-differences","tag-free-energy-difference","tag-hybridization","tag-interaction-energy","tag-interesting-chemistry","tag-steve-bachrach"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>The mysteries of stereoinduction. - Henry Rzepa&#039;s Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"The mysteries of stereoinduction. - Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"og:description\" content=\"Stereo-induction is, lets face it, a subtle phenomenon. The ratio of two stereoisomers formed in a reaction can be detected very accurately by experiment, and when converted to a free energy difference using \u0394G = -RT Ln K, this can amount to quite a small value (between 0.5 &#8211; 1.5 kcal\/mol). Can modelling reproduce effects [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"article:published_time\" content=\"2010-07-01T17:19:52+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2011-07-07T06:05:08+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene.jpg\" \/>\n<meta name=\"author\" content=\"Henry Rzepa\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Henry Rzepa\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"The mysteries of stereoinduction. - Henry Rzepa&#039;s Blog","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120","og_locale":"en_GB","og_type":"article","og_title":"The mysteries of stereoinduction. - Henry Rzepa&#039;s Blog","og_description":"Stereo-induction is, lets face it, a subtle phenomenon. 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Can modelling reproduce effects [&hellip;]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120","og_site_name":"Henry Rzepa&#039;s Blog","article_published_time":"2010-07-01T17:19:52+00:00","article_modified_time":"2011-07-07T06:05:08+00:00","og_image":[{"url":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene.jpg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"3 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"The mysteries of stereoinduction.","datePublished":"2010-07-01T17:19:52+00:00","dateModified":"2011-07-07T06:05:08+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120"},"wordCount":588,"commentCount":1,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/07\/norbornene.jpg","keywords":["chiroptical","energy differences","free energy difference","hybridization","interaction energy","Interesting chemistry","Steve Bachrach"],"articleSection":["Interesting chemistry"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2120","name":"The mysteries of stereoinduction. - 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The initial intent was to estimate the \"flattening\" energy. There are six electronic possibilities for this molecule on a metal surface. Respectively positively, or\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":248,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=248","url_meta":{"origin":2120,"position":1},"title":"Conformational analysis and enzyme activity: models for amide hydrolysis.","author":"Henry Rzepa","date":"April 12, 2009","format":false,"excerpt":"The diagram below summarizes an interesting result recently reported by Hanson and co-workers (DOI: 10.1021\/jo800706y. At ~neutral pH, compound 13 hydrolyses with a half life of 21 minutes, whereas 14 takes 840 minutes. Understanding this difference in reactivity may allow us to understand why some enzymes can catalyze the hydrolysis\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"Models for peptide cleavage.","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2009\/04\/amide-cleavage.png?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":20464,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=20464","url_meta":{"origin":2120,"position":2},"title":"The Graham reaction: Deciding upon a reasonable mechanism and curly arrow representation.","author":"Henry Rzepa","date":"February 18, 2019","format":false,"excerpt":"Students learning organic chemistry are often asked in examinations and tutorials to devise the mechanisms (as represented by curly arrows) for the core corpus of important reactions, with the purpose of learning skills that allow them to go on to improvise mechanisms for new reactions. A common question asked by\u2026","rel":"","context":"In &quot;Curly arrows&quot;","block_context":{"text":"Curly arrows","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2327"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":16308,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16308","url_meta":{"origin":2120,"position":3},"title":"Deuteronium deuteroxide. The why of pD 7.435.","author":"Henry Rzepa","date":"April 22, 2016","format":false,"excerpt":"Earlier, I constructed a possible model of hydronium hydroxide, or H3O+.OH-\u00a0One way of assessing the quality of\u00a0the model is\u00a0to\u00a0calculate\u00a0the free energy difference between it and two normal water molecules\u00a0and compare\u00a0the result to\u00a0the measured\u00a0difference. Here I apply a further test of the model using isotopes. Pure water has pH 7, which\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":11279,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=11279","url_meta":{"origin":2120,"position":4},"title":"An example of an extreme gauche effect: FSSF.","author":"Henry Rzepa","date":"September 21, 2013","format":false,"excerpt":"The best known example of the gauche effect is 1,2-difluoroethane, which exhibits a relatively small preference of ~0.5 kcal\/mol for this conformer over the anti orientation, which is also a minimum. But FSSF, which I discussed in the previous post, beats this hands down! It also, by the way, must\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"FSSF-ELF","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/09\/FSSF-ELF.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":20440,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=20440","url_meta":{"origin":2120,"position":5},"title":"Free energy relationships and their linearity: a test example.","author":"Henry Rzepa","date":"January 13, 2019","format":false,"excerpt":"Linear free energy relationships (LFER) are associated with the dawn of physical organic chemistry in the late 1930s and its objectives in understanding chemical reactivity as measured by reaction rates and equilibria. The Hammett equation is the best known of the LFERs, albeit derived \"intuitively\". It is normally applied to\u2026","rel":"","context":"In &quot;Chemical IT&quot;","block_context":{"text":"Chemical IT","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2120","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2120"}],"version-history":[{"count":0,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2120\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2120"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2120"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2120"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=2120"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}