{"id":25227,"date":"2022-06-11T07:24:19","date_gmt":"2022-06-11T06:24:19","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=25227"},"modified":"2022-08-08T10:34:36","modified_gmt":"2022-08-08T09:34:36","slug":"checking-a-conclusion-we-made-in-1987-tetrahedral-intermediates-formed-by-nitrogen-and-oxygen-attack-of-aromatic-hydroxylamines-on-acetyl-cyanide","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=25227","title":{"rendered":"Checking a conclusion we made in 1987: Tetrahedral intermediates formed by nitrogen and oxygen attack of aromatic hydroxylamines on acetyl cyanide"},"content":{"rendered":"
\n

Minds (and memories) can work in wonderful ways. In 1987[1]<\/a><\/span> we were looking at the properties of “stable” tetrahedral intermediates formed in carbonyl group reactions. The reaction involved adding phenylhydroxylamine to acetyl cyanide. NMR signals for two new species were detected, and we surmised one was due to N-attack on the carbonyl and one was due to O-attack, in each case to form a stable tetrahedral intermediate<\/a>. To try to identify which was which, 15<\/sup>N labelled hydroxylamine was used and then the 15<\/sup>N-13<\/sup>C coupling constants were measured, which could either be 1-bond<\/sup>J (for N-attack) or 2-bond<\/sup>J (for O-attack).<\/p>\n

Well, 35 years later, literally in a dream on the morning of 7th June, 2022, these results came back to me and the dream involved wondering whether we had gotten the assignments of the N- and O-species the correct way around. You see we had assigned the larger of the 15<\/sup>N-13<\/sup>C\u00a0couplings to the two bond (O-attack, species 3<\/strong> below) rather than one-bond (N-attack, species 4<\/strong> below) coupling. In 1987, the art of accurately computing such couplings was still in its infancy, but now in 2022 it is quick and easy to do. So here I report the results, which 35 years on allows a check of those assignments.<\/p>\n

\"\"<\/a><\/p>\n

The necessary calculations are assembled at FAIR DOI: 10.14469\/hpc\/10593<\/a> conducted at the \u03c9B97XD\/aug-cc-pvdz\/scrf=acetonitrile level. Firstly, it is important that the conformational space of these molecules is explored, since they contain a plethora of interesting anomeric effects.\u00a0I will not discuss this process, simply quoting what\u00a0I believe to be the lowest energy conformation for both isomers.<\/p>\n

\"\"<\/a>\"\"<\/a><\/p>\n\n\n\n\n\n\n\n\n\n\n
#<\/th>\nProperty<\/th>\nSpecies 3<\/th>\nSpecies 4<\/th>\n<\/tr>\n
1<\/td>\n\u0394G298<\/sub><\/td>\n-608.600542<\/td>\n-608.598472<\/td>\n<\/tr>\n
2<\/td>\n\u0394G215<\/sub><\/td>\n-608.586956<\/td>\n-608.585163<\/td>\n<\/tr>\n
3<\/td>\nNBO E(2)<\/td>\n14.3,19.4,10.9,8.1<\/td>\n10.0,11.2,9.9<\/td>\n<\/tr>\n
4<\/td>\n\u03b4C<\/sub> obs<\/td>\n94.3 ppm<\/td>\n85.0 ppm<\/td>\n<\/tr>\n
5<\/td>\n\u03b4C<\/sub> calc<\/td>\n97.2 (\u0394\u03b4 2.9)<\/td>\n88.1 (\u0394\u03b4 3.1)<\/td>\n<\/tr>\n
6<\/td>\nJN-C<\/sub> obs<\/td>\n2<\/sup>J \u00b12.5 Hz<\/td>\n1<\/sup>J \u00b11.3 Hz<\/td>\n<\/tr>\n
7<\/td>\nJN-C<\/sub> calc<\/td>\n2<\/sup>J +1.7<\/td>\n1<\/sup>J +0.8<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    \n
  1. The relative free energies \u0394\u0394G298<\/sub>\u00a0favour 3<\/strong> over 4<\/strong> by\u00a01.3 kcal\/mol at 298K (9:1). The article notes that 3<\/strong> is significantly<\/em> favoured over 4<\/strong> at higher temperatures (i.e. ~298K) but that the concentration of 4<\/strong> increases at lower temperatures.\u00a0<\/li>\n
  2. At 215K, \u0394\u0394G215<\/sub>\u00a0reduces to 1.1 kcal\/mol, but this equates to 13:1 at this temperature.\u00a0\u0394\u0394G215<\/sub> would need to be about 0.8 kcal\/mol for 4<\/strong> to increase (6.5:1), but these are small errors in energy and a more accurate calculation would have to be done to get this aspect correct.<\/li>\n
  3. The NBO E(2) terms indicating overlap between a lone pair and an acceptor orbital (the anomeric effect), show a dazzling variety of interactions<\/a> for such a small molecule. Species 3<\/strong> shows four significant interactions, species 4<\/strong>\u00a0one less.<\/li>\n
  4. The chemical shifts measured for 3<\/strong> and 4<\/strong> –<\/li>\n
  5. – are matched by the calculation, the error being similar for both species.<\/li>\n
  6. The 15<\/sup>N-13<\/sup>C coupling constants –<\/li>\n
  7. – are again matched, with the 1<\/sup>J coupling being about half the value of the 2<\/sup>J coupling for both obs and calculated values.<\/li>\n<\/ol>\n

    The nature of modern scientific research, and the funding available for it, means that old work is rarely re-investigated using more recent techniques. In this case, the reinvestigation does not require the molecules to be re-synthesized again, merely that a retrospective computational layer be applied. As a result of my dream of four days ago, this process has produced an interesting new layer which thankfully confirms the original conclusions.<\/p>\n

    References<\/h2>\n
    1. A.M. Lobo, M.M. Marques, S. Prabhakar, and H.S. Rzepa, \"Tetrahedral intermediates formed by nitrogen and oxygen attack of aromatic hydroxylamines on acetyl cyanide\", The Journal of Organic Chemistry<\/i>, vol. 52, pp. 2925-2927, 1987. https:\/\/doi.org\/10.1021\/jo00389a050<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

      Minds (and memories) can work in wonderful ways. In 1987 we were looking at the properties of “stable” tetrahedral intermediates formed in carbonyl group reactions. The reaction involved adding phenylhydroxylamine to acetyl cyanide. NMR signals for two new species were detected, and we surmised one was due to N-attack on the carbonyl and one was […]<\/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":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1086],"tags":[2648],"ppma_author":[2661],"class_list":["post-25227","post","type-post","status-publish","format-standard","hentry","category-reaction-mechanism-2","tag-interesting-chemistry"],"yoast_head":"\nChecking a conclusion we made in 1987: Tetrahedral intermediates formed by nitrogen and oxygen attack of aromatic hydroxylamines on acetyl cyanide - Henry Rzepa'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=25227\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Checking a conclusion we made in 1987: Tetrahedral intermediates formed by nitrogen and oxygen attack of aromatic hydroxylamines on acetyl cyanide - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"Minds (and memories) can work in wonderful ways. In 1987 we were looking at the properties of “stable” tetrahedral intermediates formed in carbonyl group reactions. The reaction involved adding phenylhydroxylamine to acetyl cyanide. 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Dan Singleton, in whose group the original KIE (kinetic isotope measurements) were made, has kindly\u00a0pointed out\u00a0on this blog that his was a mixed-phase reaction, and that mechanistic comparison\u2026","rel":"","context":"In "reaction mechanism"","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":10184,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10184","url_meta":{"origin":25227,"position":2},"title":"Intermediates in oxime formation from hydroxylamine and propanone: now you see them, now you don’t.","author":"Henry Rzepa","date":"April 14, 2013","format":false,"excerpt":"A recent theme here has been to subject to scrutiny well-known mechanisms supposedly involving intermediates. These transients can often involve the creation\/annihilation of charge separation resulting from \u00a0proton transfers, something that a cyclic mechanism can avoid. Here I revisit the formation of an oxime from hydroxylamine and propanone, but with\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"N-pre","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/04\/N-pre.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":26340,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=26340","url_meta":{"origin":25227,"position":3},"title":"The “double-headed” curly arrow as used in mechanistic representations.","author":"Henry Rzepa","date":"August 29, 2023","format":false,"excerpt":"The schematic representation of a chemical reaction mechanism is often drawn using a palette of arrows connecting or annotating the various molecular structures involved. These can be selected from a chemical arrows palette, taken for this purpose from the commonly used structure drawing program Chemdraw. Explanations of how to apply\u2026","rel":"","context":"In "Curly arrows"","block_context":{"text":"Curly arrows","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2327"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2023\/08\/IMG_3157-131x300.jpeg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":13047,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13047","url_meta":{"origin":25227,"position":4},"title":"A computed mechanistic pathway for the formation of an amide from an acid and an amine in non-polar solution.","author":"Henry Rzepa","date":"November 12, 2014","format":false,"excerpt":"In London, one has the pleasures of attending occasional one day meetings at the Burlington House, home of the Royal Society of Chemistry. On November 5th this year, there was an excellent\u00a0meeting on the topic of Challenges in Catalysis,\u00a0and you can see the speakers and (some of) their slides here.\u2026","rel":"","context":"In "reaction mechanism"","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":3576,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=3576","url_meta":{"origin":25227,"position":5},"title":"The formation of cyanohydrins: re-writing the text books. ! or ?","author":"Henry Rzepa","date":"March 4, 2011","format":false,"excerpt":"Nucleophilic addition of cyanide to a ketone or aldehyde is a standard reaction for introductory organic chemistry. But is all as it seems? The reaction is often represented as below, and this seems simple enough. But attention to detail suggests that, HCN being a weak acid, there will be only\u2026","rel":"","context":"In \"acidic solutions\"","block_context":{"text":"acidic solutions","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=acidic-solutions"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/03\/cyano1.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\/25227","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=25227"}],"version-history":[{"count":22,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/25227\/revisions"}],"predecessor-version":[{"id":25259,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/25227\/revisions\/25259"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=25227"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=25227"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=25227"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=25227"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}