{"id":7258,"date":"2012-07-20T22:16:17","date_gmt":"2012-07-20T21:16:17","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=7258"},"modified":"2018-02-05T14:23:15","modified_gmt":"2018-02-05T14:23:15","slug":"the-first-curly-arrows-lead-to-this","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=7258","title":{"rendered":"The first curly arrows&#8230;lead to this?"},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"7258\">\n<p>Little did I imagine, when I <a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=7234\" target=\"_blank\" rel=\"noopener\">discovered<\/a> the original example of using curly arrows to express mechanism, that the molecule described there might be rather too anarchic to use in my introductory tutorials on organic chemistry. Why? It simply breaks the (it has to be said to some extent informal) <a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=2737\" target=\"_blank\" rel=\"noopener\">rules<\/a>! Consider the dimerisation of nitrosomethane (in fact a <a href=\"http:\/\/dx.doi.org\/10.1021\/jo051236u\" target=\"_blank\" rel=\"noopener\">well-known <\/a>equilibrium).<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-7259\" title=\"dim_nitrosomethane\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/07\/dim_nitrosomethane.svg\" alt=\"\" \/><\/p>\n<p>Curly arrow pushing for this reaction results in two arrows heading in effect towards the same bond, at the same time! The result has two adjacent nitrogen atoms each with (formal) positive charges on them, and the N&#8230;N bond order goes from zero to two in a single step. Surely this cannot be allowed to happen as shown above? Well, the IRC (intrinsic reaction coordinate) <a href=\"http:\/\/hdl.handle.net\/10042\/20248\" target=\"_blank\" rel=\"noopener\">computed<\/a> from a \u03c9B97XD\/6-311G(d,p) calculation is shown below. The barrier is small, the profile uneventful. I conclude that if I ever see a student exam script showing two curly arrows heading <a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=1158\" target=\"_blank\" rel=\"noopener\">directly towards<\/a> the same bond at the same time, it might even deserve to be graded correct!\u00a0<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-7260\" title=\"NO_dim\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/07\/NO_dim.gif\" alt=\"\" width=\"393\" height=\"297\" \/><\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-7261\" title=\"NO_dim\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/07\/NO_dim.svg\" alt=\"\" \/><br \/>\n <img decoding=\"async\" class=\"aligncenter size-full wp-image-7262\" title=\"NO_dimg\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/07\/NO_dimg.svg\" alt=\"\" \/><\/p>\n<!-- kcite active, but no citations found -->\n<\/div> <!-- kcite-section 7258 -->","protected":false},"excerpt":{"rendered":"<p>Little did I imagine, when I discovered the original example of using curly arrows to express mechanism, that the molecule described there might be rather too anarchic to use in my introductory tutorials on organic chemistry. Why? It simply breaks the (it has to be said to some extent informal) rules! Consider the dimerisation of [&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":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}},"categories":[2327],"tags":[879,843,373],"ppma_author":[2661],"class_list":["post-7258","post","type-post","status-publish","format-standard","hentry","category-curl-arrows","tag-dimer","tag-reaction-mechanism","tag-tutorial-material"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>The first curly arrows...lead to this? - 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=7258\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"The first curly arrows...lead to this? - Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"og:description\" content=\"Little did I imagine, when I discovered the original example of using curly arrows to express mechanism, that the molecule described there might be rather too anarchic to use in my introductory tutorials on organic chemistry. Why? It simply breaks the (it has to be said to some extent informal) rules! Consider the dimerisation of [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=7258\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"article:published_time\" content=\"2012-07-20T21:16:17+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2018-02-05T14:23:15+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/07\/dim_nitrosomethane.svg\" \/>\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=\"1 minute\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"The first curly arrows...lead to this? - 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=7258","og_locale":"en_GB","og_type":"article","og_title":"The first curly arrows...lead to this? - Henry Rzepa&#039;s Blog","og_description":"Little did I imagine, when I discovered the original example of using curly arrows to express mechanism, that the molecule described there might be rather too anarchic to use in my introductory tutorials on organic chemistry. 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