{"id":17692,"date":"2017-04-01T13:10:47","date_gmt":"2017-04-01T12:10:47","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=17692"},"modified":"2017-04-12T09:03:31","modified_gmt":"2017-04-12T08:03:31","slug":"what-is-the-calculated-structure-of-a-norbornyl-cation-anion-pair-in-water","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692","title":{"rendered":"What is the (calculated) structure of a norbornyl cation anion-pair in water?"},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"17692\">\n<p>In a <a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=17633#comment-227419\">comment appended<\/a> to an earlier post, I mused about the magnitude of the force constant relating to the interconversion between a classical and a non-classical structure for the norbornyl cation. Most calculations indicate the force constant for an &#8220;isolated&#8221; symmetrical cation\u00a0is +ve, which means it is a true minimum and not a transition state for a [1,2] shift. The latter would have been required if the species equilibrated\u00a0between two classical carbocations. I then pondered\u00a0what might happen to both the magnitude and the sign of this force constant if various layers of solvation and eventually a counter-ion were to be applied to the molecule, so that a bridge of sorts between the different states of solid crystals, superacid and aqueous solutions might be built.<\/p>\n<p>I augmented the model in stages. The results are summarised in the table below.<\/p>\n<ul>\n<li>Firstly, adding a self-consistent-reaction-field (SCRF) continuum model for water.<\/li>\n<li>Then adding to that four explicit water molecules symmetrically arranged around the four C-H groups mostly likely to be solvated <em>via<\/em> hydrogen bonds.<\/li>\n<li>The final model added a chloride anion to complete the ion pair and a further three water molecules to act as its solvation sphere.\u00a0A\u00a0search of the Cambridge structure database for any instances of a molecule with a designated C<sup>+<\/sup> and a nucleophilic halide<sup>&#8211;<\/sup> with zero coordination number\u00a0(a free halide anion) reveals no hits; such ion-pairs are clearly very unstable towards covalent bond formation, existing if at all only as transient species or when the counter-ion is non-nucleophilic such as R<sub>4<\/sub>B<sup>&#8211;<\/sup>.<\/li>\n<\/ul>\n<table border=\"1\">\n<tbody>\n<tr>\n<th colspan=\"5\">Calculated geometries,\u00a0Def2-TZVPP\/SCRF=water<\/th>\n<\/tr>\n<tr>\n<th>\n<p>Model<\/p>\n<\/th>\n<th>\n<p>Apical C-C<\/p>\n<p>distance,\u00c5<\/p>\n<\/th>\n<th>\n<p>Basal C-C<\/p>\n<p>distance,\u00c5<\/p>\n<\/th>\n<th>\n<p>\u03bd [1,2]<\/p>\n<p>cm<sup>-1<\/sup><\/p>\n<\/th>\n<th>DataDOI<\/th>\n<\/tr>\n<tr>\n<td>Vacuum, cation<br \/>\nB3LYP+D3BJ<\/td>\n<td>1.888<\/td>\n<td>1.388<\/td>\n<td>+140<\/td>\n<td><a href=\"http:\/\/doi.org\/10.14469\/hpc\/2410\">10.14469\/hpc\/2410<\/a><\/td>\n<\/tr>\n<tr>\n<td>Vacuum, cation<br \/>\n\u03c9B97XD<\/td>\n<td>1.830<\/td>\n<td>1.388<\/td>\n<td>+235<\/td>\n<td><a href=\"http:\/\/doi.org\/10.14469\/hpc\/2409\">10.14469\/hpc\/2409<\/a><\/td>\n<\/tr>\n<tr>\n<td>Vacuum, cation<br \/>\nB2PLYPD3<\/td>\n<td>1.872<\/td>\n<td>1.390<\/td>\n<td>+194<\/td>\n<td><a href=\"http:\/\/doi.org\/10.14469\/hpc\/2238\">10.14469\/hpc\/2238<\/a><\/td>\n<\/tr>\n<tr>\n<td>Vacuum, cation<br \/>\nCCSD<\/td>\n<td>1.845<\/td>\n<td>1.389<\/td>\n<td>&#8212;<\/td>\n<td><a href=\"http:\/\/doi.org\/10.14469\/hpc\/2441\">10.14469\/hpc\/2441<\/a><\/td>\n<\/tr>\n<tr>\n<td>SCRF, cation<br \/>\u03c9B97XD<\/td>\n<td>1.819<\/td>\n<td>1.387<\/td>\n<td>+236<\/td>\n<td><a href=\"http:\/\/doi.org\/10.14469\/hpc\/2413\">10.14469\/hpc\/2413<\/a><\/td>\n<\/tr>\n<tr>\n<td>SCRF, cation<br \/>\nB2PLYPD3<\/td>\n<td>1.858<\/td>\n<td>1.388<\/td>\n<td>+202<\/td>\n<td><a href=\"http:\/\/doi.org\/10.14469\/hpc\/2243\">10.14469\/hpc\/2243<\/a><\/td>\n<\/tr>\n<tr>\n<td>SCRF, cation<br \/>\nCCSD<\/td>\n<td>1.833<\/td>\n<td>1.387<\/td>\n<td>&#8212;<\/td>\n<td><a href=\"http:\/\/doi.org\/10.14469\/hpc\/2441\">10.14469\/hpc\/2441<\/a><\/td>\n<\/tr>\n<tr>\n<td>SCRF+4H2O, cation<br \/>\nB2PLYPD3<\/td>\n<td>1.838<\/td>\n<td>1.390<\/td>\n<td>+254<\/td>\n<td><a href=\"http:\/\/doi.org\/10.14469\/hpc\/2246\">10.14469\/hpc\/2246<\/a><\/td>\n<\/tr>\n<tr>\n<td>SCRF+7H2O+Cl<sup>&#8211;<\/sup> ion pair<br \/>\nB3LYP+D3BJ<\/td>\n<td>1.593, 2.485<\/td>\n<td>1.510<\/td>\n<td>&#8211;<\/td>\n<td><a href=\"https:\/\/doi.org\/10.14469\/hpc\/2408\">10.14469\/hpc\/2408<\/a><br \/>\n<a href=\"https:\/\/doi.org\/10.14469\/hpc\/2439\">10.14469\/hpc\/2439<\/a><\/td>\n<\/tr>\n<tr>\n<td>SCRF+7H2O+Cl<sup>&#8211;<\/sup> ion pair<br \/>\n\u03c9B97XD<\/td>\n<td>1.795, 1.817<\/td>\n<td>1.385<\/td>\n<td>+249<sup>\u2020<\/sup><\/td>\n<td><a href=\"https:\/\/doi.org\/10.14469\/hpc\/2411\">10.14469\/hpc\/2411<\/a><\/td>\n<\/tr>\n<tr>\n<td>SCRF+8H2O+Cl<sup>&#8211;<\/sup> ion pair<br \/>\n\u03c9B97XD<\/td>\n<td>1.771, 1.822<\/td>\n<td>1.388<\/td>\n<td>+249<sup>\u2020<\/sup><\/td>\n<td><a href=\"https:\/\/doi.org\/10.14469\/hpc\/2468\">10.14469\/hpc\/2468<\/a><\/td>\n<\/tr>\n<tr>\n<td>SCRF+8H2O+Cl<sup>&#8211;<\/sup> ion pair<br \/>\nMN15<\/td>\n<td>1.756, 1.822<\/td>\n<td>1.390<\/td>\n<td>+266<sup>\u2020<\/sup><\/td>\n<td><a href=\"https:\/\/doi.org\/10.14469\/hpc\/2452\">10.14469\/hpc\/2452<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><sup>\u2020<\/sup><small>246 cm<sup>-1<\/sup> when refactored mass-weighting eliminates mode mixing between this mode and the surrounding water\/chloride molecules, as shown below:<br \/>\n <img decoding=\"async\" class=\"aligncenter size-full wp-image-17980\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/N1.gif\" alt=\"\" width=\"200\" \/><\/small><\/p>\n<hr \/>\n<p>As the solvation and environment of the cationic model improves, the apical distance shortens significantly. But the crunch comes when a chloride counter-anion is added to desymmetrise this environment. Using the veritable B3LYP functional, but with an added dispersion term (D3BJ) and starting from a partially optimised ion-pair geometry, this geometry optimisation (shown animated below) rapidly quenches the ion-pair to form a covalent norbornyl chloride. It is noteworthy that the magnitude of the [1,2] vibration force constant (\u2261140 cm<sup>-1<\/sup>) is rather smaller using B3LYP than the other methods explored.\u00a0<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-17919\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/03\/b3lypd3bj.gif\" alt=\"\" width=\"378\" height=\"378\" \/><\/p>\n<p>The next method tried was\u00a0\u03c9B97XD, which contains a built-in dispersion term (D2) and also reveals a larger force constant for the gas phase [1,2] shift (\u2261235 cm<sup>-1<\/sup>). Starting from the same initial geometry as the B3LYP calculation, optimisation of the ion-pair proceeds remarkably slowly<sup>\u2021<\/sup> (even using the <tt>recalcfc=5<\/tt> keyword to recompute the force constant\u00a0matrix\/search direction every five cycles to improve behaviour), suggesting that the potential energy surface is very flat indeed. The final geometry retains the ion-pair character (dipole moment 23D) but reveals distinct asymmetry in the resulting bridged\u00a0structure, for which the [1,2] shift is \u03bd 249 cm<sup>-1<\/sup>.<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-17971\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/025.jpg\" alt=\"\" width=\"350\" srcset=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/025.jpg 646w, https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/025-276x300.jpg 276w\" sizes=\"(max-width: 646px) 100vw, 646px\" \/><\/p>\n<p>It is clear that the structure of the norbornyl ion-pair is balanced on a knife-edge. Perturbations such as change of density functional (<em>e.g.<\/em> B3LYP+D3BJ) can topple it over that edge. Weaker asymmetry can also be induced by the presence of the contact-anion and water molecules. I have selected just one solvation model, which includes seven water molecules and an explicit anion. Clearly a more statistical and dynamical approach to the number of waters and their orientation around the norbornyl ring system would sample a much larger set of models. It may be that some of them do again topple the symmetric bridge structure off its delicate perch whilst others retain it. Perhaps this is why the results from the enormous range of solvolysis mechanisms are so difficult to always reconcile. A crystal structure may also be a relatively large perturbation to the solution structure of this species!<\/p>\n<p>The title of one of the last articles published\u00a0(posthumously) with Paul Schleyer as a co-author<span id=\"cite_ITEM-17692-0\" name=\"citation\"><a href=\"#ITEM-17692-0\">[1]<\/a><\/span> is &#8220;<em>Norbornyl Cation Isomers Still Fascinate<\/em>&#8220;. True indeed.<\/p>\n<hr \/>\n<p><sup>\u2021<\/sup>This renders refinement using the B2PLYPD3 double-hybrid method<span id=\"cite_ITEM-17692-1\" name=\"citation\"><a href=\"#ITEM-17692-1\">[2]<\/a><\/span> an exceptionally slow process, since computing the force constant matrix using this method is very\u00a0computationally intensive at the selected triple-\u03b6 level. This calculation uses a \u03c9B97XD force constant matrix as a seed for the optimisation (DOI: <a href=\"http:\/\/doi.org\/10.14469\/hpc\/2424\">10.14469\/hpc\/2424<\/a>) with the result of a collapse of the ion-pair, as was also observed using the B3LYP-D3BJ functional.<\/p>\n<p><!-- \n\n\n\n\n<td>SCRF+7H2O+Cl<sup>-<\/sup> ion pair<br \/>\nB2PLYPD3\n\n\n\n<td>1.791, 1.904<\/td>\n\n\n\n\n<td>1.389<\/td>\n\n\n\n\n<td>?<\/td>\n\n\n\n\n<td><a href=\"https:\/\/doi.org\/10.14469\/hpc\/24??\">10.14469\/hpc\/24??<\/a><\/td>\n\n\n\n\n\n--><\/p>\n<h2>References<\/h2>\n    <ol class=\"kcite-bibliography csl-bib-body\"><li id=\"ITEM-17692-0\">P.V.R. Schleyer, V.V. Mainz, and E.T. Strom, \"Norbornyl Cation Isomers Still Fascinate\", <i>ACS Symposium Series<\/i>, pp. 139-168, 2015. <a href=\"https:\/\/doi.org\/10.1021\/bk-2015-1209.ch007\">https:\/\/doi.org\/10.1021\/bk-2015-1209.ch007<\/a>\n\n<\/li>\n<li id=\"ITEM-17692-1\">L. Goerigk, and S. Grimme, \"Efficient and Accurate Double-Hybrid-Meta-GGA Density Functionals\u2014Evaluation with the Extended GMTKN30 Database for General Main Group Thermochemistry, Kinetics, and Noncovalent Interactions\", <i>Journal of Chemical Theory and Computation<\/i>, vol. 7, pp. 291-309, 2010. <a href=\"https:\/\/doi.org\/10.1021\/ct100466k\">https:\/\/doi.org\/10.1021\/ct100466k<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> <!-- kcite-section 17692 -->","protected":false},"excerpt":{"rendered":"<p>In a comment appended to an earlier post, I mused about the magnitude of the force constant relating to the interconversion between a classical and a non-classical structure for the norbornyl cation. Most calculations indicate the force constant for an &#8220;isolated&#8221; symmetrical cation\u00a0is +ve, which means it is a true minimum and not a transition [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":true,"_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":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1745,4,1086],"tags":[2083,557,1395,2114,2113,145,1133,1442,142,1849,2115],"ppma_author":[2661],"class_list":["post-17692","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining","category-interesting-chemistry","category-reaction-mechanism-2","tag-carbocations","tag-chemical-bonding","tag-chemistry","tag-constant-matrixsearch-direction","tag-continuum-model-for-water","tag-gas-phase","tag-paul-schleyer","tag-physical-organic-chemistry","tag-potential-energy-surface","tag-reactive-intermediates","tag-superacid-and-aqueous-solutions"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.5 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>What is the (calculated) structure of a norbornyl cation anion-pair in water? - 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=17692\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"What is the (calculated) structure of a norbornyl cation anion-pair in water? - Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"og:description\" content=\"In a comment appended to an earlier post, I mused about the magnitude of the force constant relating to the interconversion between a classical and a non-classical structure for the norbornyl cation. Most calculations indicate the force constant for an &#8220;isolated&#8221; symmetrical cation\u00a0is +ve, which means it is a true minimum and not a transition [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"article:published_time\" content=\"2017-04-01T12:10:47+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2017-04-12T08:03:31+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/N1.gif\" \/>\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=\"4 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"What is the (calculated) structure of a norbornyl cation anion-pair in water? - 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=17692","og_locale":"en_GB","og_type":"article","og_title":"What is the (calculated) structure of a norbornyl cation anion-pair in water? - Henry Rzepa&#039;s Blog","og_description":"In a comment appended to an earlier post, I mused about the magnitude of the force constant relating to the interconversion between a classical and a non-classical structure for the norbornyl cation. Most calculations indicate the force constant for an &#8220;isolated&#8221; symmetrical cation\u00a0is +ve, which means it is a true minimum and not a transition [&hellip;]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692","og_site_name":"Henry Rzepa&#039;s Blog","article_published_time":"2017-04-01T12:10:47+00:00","article_modified_time":"2017-04-12T08:03:31+00:00","og_image":[{"url":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/N1.gif","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"4 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"What is the (calculated) structure of a norbornyl cation anion-pair in water?","datePublished":"2017-04-01T12:10:47+00:00","dateModified":"2017-04-12T08:03:31+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692"},"wordCount":826,"commentCount":7,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/N1.gif","keywords":["Carbocations","chemical bonding","Chemistry","constant matrix\/search direction","continuum model for water","gas phase","Paul Schleyer","Physical organic chemistry","potential energy surface","Reactive intermediates","superacid and aqueous solutions"],"articleSection":["crystal_structure_mining","Interesting chemistry","reaction mechanism"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692","name":"What is the (calculated) structure of a norbornyl cation anion-pair in water? - Henry Rzepa&#039;s Blog","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692#primaryimage"},"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/N1.gif","datePublished":"2017-04-01T12:10:47+00:00","dateModified":"2017-04-12T08:03:31+00:00","author":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"breadcrumb":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692"]}]},{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692#primaryimage","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/N1.gif","contentUrl":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/N1.gif","width":331,"height":379},{"@type":"BreadcrumbList","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17692#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog"},{"@type":"ListItem","position":2,"name":"What is the (calculated) structure of a norbornyl cation anion-pair in water?"}]},{"@type":"WebSite","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/","name":"Henry Rzepa&#039;s Blog","description":"Chemistry with a twist","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-GB"},{"@type":"Person","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281","name":"Henry Rzepa","image":{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g370be3a7397865e4fd161aefeb0a5a85","url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","caption":"Henry Rzepa"},"description":"Henry Rzepa is Emeritus Professor of Computational Chemistry at Imperial College London.","sameAs":["https:\/\/orcid.org\/0000-0002-8635-8390"],"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?author=1"}]}},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/pDef7-4Bm","jetpack-related-posts":[{"id":17633,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17633","url_meta":{"origin":17692,"position":0},"title":"George Olah and the norbornyl cation.","author":"Henry Rzepa","date":"March 10, 2017","format":false,"excerpt":"George Olah passed away on March 8th. He was part of the generation of scientists in the post-war 1950s who had access to chemical instrumentation that truly revolutionised chemistry. In particular he showed how the then newly available NMR spectroscopy illuminated structures of cations in solvents such \"Magic acid\". The\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":17805,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17805","url_meta":{"origin":17692,"position":1},"title":"Silyl cations?","author":"Henry Rzepa","date":"March 23, 2017","format":false,"excerpt":"It is not only the non-classical norbornyl cation that has proved controversial in the past. A colleague mentioned at lunch (thanks Paul!) that tri-coordinate group 14 cations such as R3Si+ have also had an interesting history. Here I take a brief look at some of these systems. Their initial characterisations,\u2026","rel":"","context":"In &quot;crystal_structure_mining&quot;","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/03\/164-1024x748.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":17662,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17662","url_meta":{"origin":17692,"position":2},"title":"Expanding on the curious connection between the norbornyl cation and small-ring aromatics.","author":"Henry Rzepa","date":"March 12, 2017","format":false,"excerpt":"This is another of those posts that has morphed from an earlier one noting\u00a0the death of the great chemist George Olah. The discussion about the norbornyl cation concentrated on whether this species existed in a single minimum symmetric energy well (the non-classical Winstein\/Olah proposal) or a double minimum well connected\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":17702,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17702","url_meta":{"origin":17692,"position":3},"title":"How does methane invert (its configuration)?","author":"Henry Rzepa","date":"March 16, 2017","format":false,"excerpt":"This is a spin-off from the table I constructed here for further chemical examples of the classical\/non-classical norbornyl cation conundrum. One possible entry would include the transition state for inversion of methane via a square planar geometry as compared with e.g. NiH4 for which the square planar motif is its\u2026","rel":"","context":"In &quot;reaction mechanism&quot;","block_context":{"text":"reaction mechanism","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1086"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":17858,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17858","url_meta":{"origin":17692,"position":4},"title":"First, hexacoordinate carbon \u2013 now pentacoordinate oxygen?","author":"Henry Rzepa","date":"March 25, 2017","format":false,"excerpt":"The previous post demonstrated the simple iso-electronic progression from six-coordinate carbon to five coordinate nitrogen. Here, a further progression to oxygen is investigated computationally. The systems are formally constructed from a cyclobutadienyl di-anion and firstly the HO5+ cation, giving a tri-cationic complex. There are no examples of the resulting motif\u00a0in\u2026","rel":"","context":"In &quot;Bond slam&quot;","block_context":{"text":"Bond slam","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2237"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":4893,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=4893","url_meta":{"origin":17692,"position":5},"title":"Some fun with no-go areas of chemistry: cyclobutadiene.","author":"Henry Rzepa","date":"September 18, 2011","format":false,"excerpt":"Organic chemistry has some no-go areas, where few molecules dare venture. One of them is described by a concept known as anti-aromaticity. Whereas aromatic molecules are favoured species, their anti-equivalent is avoided. I previously illustrated this (H\u00fcckel rule) with cyclopropenium anion. Now I take a look at cyclobutadiene, for 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":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/09\/cbdzw.jpg?resize=350%2C200","width":350,"height":200},"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\/17692","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=17692"}],"version-history":[{"count":73,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/17692\/revisions"}],"predecessor-version":[{"id":18115,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/17692\/revisions\/18115"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=17692"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=17692"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=17692"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=17692"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}