{"id":28187,"date":"2025-01-08T10:04:35","date_gmt":"2025-01-08T10:04:35","guid":{"rendered":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=28187"},"modified":"2025-01-08T10:29:10","modified_gmt":"2025-01-08T10:29:10","slug":"molecules-of-the-year-2024-a-crystal-structure-perspective-on-anti-bredt-olefins","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=28187","title":{"rendered":"Molecules of the Year 2024: A crystal structure perspective on anti-Bredt olefins."},"content":{"rendered":"
\n

Each year C&E News publishes a list of candidates for the Molecule of the Year. For 2024<\/a> the list is (in order of votes cast for each)<\/p>\n

    \n
  1. Mirror-image cyclodextrin [1]<\/a><\/span><\/li>\n
  2. Molecular shuttle in a box [2]<\/a><\/span><\/li>\n
  3. Rule-bending strained alkene<\/strong> [3]<\/a><\/span><\/li>\n
  4. First soluble promethium complex [4]<\/a><\/span><\/li>\n
  5. Single-electron carbon-carbon bond [5]<\/a><\/span><\/li>\n
  6. Hot MOF for capturing carbon[6]<\/a><\/span><\/li>\n<\/ol>\n

    I dealt at length with entry 5 (single-electron carbon-carbon bond) \u00a0last year, my conclusions rather negating the statement made about it being an example of such a bond. Here\u00a0I take a look at number 3, A solution to the anti-Bredt olefin synthesis problem<\/em>.[3]<\/a><\/span> Four molecules below (1-4<\/strong>) were identified as examples of anti-Bredt rule compounds from trapping experiments (their properties such as NMR or indeed structures are not reported). Julius Bredt had predicted 100 years ago\u00a0would be particularly unstable.[7]<\/a><\/span><\/p>\n

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

    One way of putting these molecules into context is to search for any similarly strained alkenes in the Cambridge crystal database. The search query used defined a centroid of the plane defined by the three carbon atoms attached to the bridgehead carbon atom, and then the distance from that centroid to the carbon atom itself. For entirely \u00a0planar coordination of that atom, the distance would be ~zero and the deviation from zero is one way of measuring how strained the alkene is.<\/p>\n

    \"\"<\/p>\n

    The results of the search (for which fullerenes are excluded as special cases) is shown below. The upward limits of the centroid distance are between ~0.3 – 0.34\u00c5; the outlier at 0.47\u00c5 appears to be an error, since the corresponding C=C distance is 1.565\u00c5.<\/p>\n

    \"\"

    Screenshot<\/p><\/div>\n

    For comparison, the centroid distance to four-coordinate carbon (a central carbon with four attached carbon ligands) is shown below – the most probable value being ~0.51\u00c5.<\/p>\n

    \"\"

    Screenshot<\/p><\/div>\n

    Since compounds 1-4<\/strong> were not actually isolated, no crystal structures or NMR data are available. \u03c9B97XD\/Def2-TZVPP calculations were performed to establish trends in these properties (FAIR Data [8]<\/a><\/span>).<\/p>\n\n\n\n\n\n\n\n
    Molecule<\/th>\nCentroid distance, \u00c5<\/th>\nC=C length<\/th>\n\u03bd cm-1<\/sup><\/th>\n\u03b4 1<\/sup>H<\/th>\n\u03b4 13<\/sup>C<\/th>\n<\/tr>\n
    1 (“ABO 12”)<\/td>\n0.510 (adduct 62 [3]<\/a><\/span>)<\/td>\n1.346<\/td>\n1611<\/td>\n6.76<\/td>\n189.8<\/td>\n<\/tr>\n
    2<\/td>\n0.505 (adduct 58 [3]<\/a><\/span>)<\/td>\n1.349<\/td>\n1594<\/td>\n6.76<\/td>\n196.8<\/td>\n<\/tr>\n
    3<\/td>\n0.341 (adduct 72 [3]<\/a><\/span>)<\/td>\n1.341<\/td>\n1684<\/td>\n5.84<\/td>\n170.3<\/td>\n<\/tr>\n
    4<\/td>\n0.357 (adduct 68 [3]<\/a><\/span>)<\/td>\n1.336<\/td>\n1694<\/td>\n6.26<\/td>\n173.3<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    For compounds 1-2<\/strong>, the largest ring of the three associated with the bridgehead carbon is six, whereas for compounds 3-4<\/strong> it is seven. This is reflected in the values shown in the table above.\u00a0The centroid distance for the six-ring examples is close to 0.5\u00c5, for which no examples exist in the crystal structure database.\u00a0The centroid distance for the seven-ring examples is 0.34-0.35\u00c5, for which a number of crystalline examples are evident.\u00a0It seems likely then that compounds 3-4<\/strong> stand a better chance of being isolated as such, rather than having their existence inferred from the cycloadducts they form. Perhaps a modification to the experimental procedures might accomplish this?\u00a0The predicted 1<\/sup>H and 13<\/sup>C spectra are shown in the table to aid identification if this is ever achieved. Also noteworthy are the C=C stretching vibrations, which are lowered significantly for 1-2<\/strong> compared to 3-4.<\/strong><\/p>\n

    Its good to have experimental evidence for compounds that 100 years ago were predicted to be unusually unstable. Perhaps the next step is to isolate them as pure compounds and study their properties.<\/p>\n

    References<\/h2>\n
    1. Y. Wu, S. Aslani, H. Han, C. Tang, G. Wu, X. Li, H. Wu, C.L. Stern, Q. Guo, Y. Qiu, A.X. Chen, Y. Jiao, R. Zhang, A.H.G. David, D.W. Armstrong, and J. Fraser Stoddart, \"Mirror-image cyclodextrins\", Nature Synthesis<\/i>, vol. 3, pp. 698-706, 2024. https:\/\/doi.org\/10.1038\/s44160-024-00495-8<\/a>\n\n<\/li>\n
    2. S. Ib\u00e1\u00f1ez, P. Salv\u00e0, L.N. Dawe, and E. Peris, \"Guest\u2010Shuttling in a Nanosized Metallobox\", Angewandte Chemie International Edition<\/i>, vol. 63, 2024. https:\/\/doi.org\/10.1002\/anie.202318829<\/a>\n\n<\/li>\n
    3. L. McDermott, Z.G. Walters, S.A. French, A.M. Clark, J. Ding, A.V. Kelleghan, K.N. Houk, and N.K. Garg, \"A solution to the anti-Bredt olefin synthesis problem\", Science<\/i>, vol. 386, 2024. https:\/\/doi.org\/10.1126\/science.adq3519<\/a>\n\n<\/li>\n
    4. D.M. Driscoll, F.D. White, S. Pramanik, J.D. Einkauf, B. Ravel, D. Bykov, S. Roy, R.T. Mayes, L.H. Delmau, S.K. Cary, T. Dyke, A. Miller, M. Silveira, S.M. VanCleve, S.M. Davern, S. Jansone-Popova, I. Popovs, and A.S. Ivanov, \"Observation of a promethium complex in solution\", Nature<\/i>, vol. 629, pp. 819-823, 2024. https:\/\/doi.org\/10.1038\/s41586-024-07267-6<\/a>\n\n<\/li>\n
    5. T. Shimajiri, S. Kawaguchi, T. Suzuki, and Y. Ishigaki, \"Direct evidence for a carbon\u2013carbon one-electron \u03c3-bond\", Nature<\/i>, vol. 634, pp. 347-351, 2024. https:\/\/doi.org\/10.1038\/s41586-024-07965-1<\/a>\n\n<\/li>\n
    6. R.C. Rohde, K.M. Carsch, M.N. Dods, H.Z.H. Jiang, A.R. McIsaac, R.A. Klein, H. Kwon, S.L. Karstens, Y. Wang, A.J. Huang, J.W. Taylor, Y. Yabuuchi, N.V. Tkachenko, K.R. Meihaus, H. Furukawa, D.R. Yahne, K.E. Engler, K.C. Bustillo, A.M. Minor, J.A. Reimer, M. Head-Gordon, C.M. Brown, and J.R. Long, \"High-temperature carbon dioxide capture in a porous material with terminal zinc hydride sites\", Science<\/i>, vol. 386, pp. 814-819, 2024. https:\/\/doi.org\/10.1126\/science.adk5697<\/a>\n\n<\/li>\n
    7. J. Bredt, \"\u00dcber sterische Hinderung in Br\u00fcckenringen (Bredtsche Regel) und \u00fcber die <i>meso<\/i>\u2010<i>trans<\/i>\u2010Stellung in kondensierten Ringsystemen des Hexamethylens\", Justus Liebigs Annalen der Chemie<\/i>, vol. 437, pp. 1-13, 1924. https:\/\/doi.org\/10.1002\/jlac.19244370102<\/a>\n\n<\/li>\n
    8. H. Rzepa, \"Molecules of the Year - 2024. A crystal structure perspective on anti-Bredt olefins.\", 2025. https:\/\/doi.org\/10.14469\/hpc\/14898<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

      Each year C&E News publishes a list of candidates for the Molecule of the Year. For 2024 the list is (in order of votes cast for each) Mirror-image cyclodextrin Molecular shuttle in a box Rule-bending strained alkene First soluble promethium complex Single-electron carbon-carbon bond Hot MOF for capturing carbon I dealt at length with entry […]<\/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":[4],"tags":[],"ppma_author":[2661],"class_list":["post-28187","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry"],"yoast_head":"\nMolecules of the Year 2024: A crystal structure perspective on anti-Bredt olefins. - 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=28187\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Molecules of the Year 2024: A crystal structure perspective on anti-Bredt olefins. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"Each year C&E News publishes a list of candidates for the Molecule of the Year. 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Or a weak carbon-carbon interaction?","author":"Henry Rzepa","date":"October 1, 2024","format":false,"excerpt":"More than 100 years ago, before the quantum mechanical treatment of molecules had been formulated, G. N. Lewis proposed a simple model for chemical bonding that is still taught today. This is the idea of the three categories of bond we know as single, double and triple, comprising respectively two,\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":"","src":"","width":0,"height":0},"classes":[]},{"id":26601,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=26601","url_meta":{"origin":28187,"position":2},"title":"Molecules of the year: 2023","author":"Henry Rzepa","date":"December 28, 2023","format":false,"excerpt":"The Science education unit at the ACS publication C&EN publishes its list of molecules of the year (as selected by the editors and voted upon by the readers) in December. Here are some observations about three of this year's batch. Diberyllocene with its unusual Be-Be bond has already beeen covered\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2023\/12\/CF.gif?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":9973,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9973","url_meta":{"origin":28187,"position":3},"title":"A (very) short history of shared-electron bonds.","author":"Henry Rzepa","date":"March 26, 2013","format":false,"excerpt":"The concept of a shared electron bond and its property of an order is almost 100 years old in modern form, when G. N. Lewis suggested a model for single and double bonds that involved sharing either 2 or 4 electrons between a pair of atoms. We tend to think\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":"Click for 3D","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/PYRDRE.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":2828,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2828","url_meta":{"origin":28187,"position":4},"title":"Can a cyclobutadiene and carbon dioxide co-exist in a calixarene cavity?","author":"Henry Rzepa","date":"November 19, 2010","format":false,"excerpt":"On 8th August this year, I posted on a fascinating article that had just appeared in Science in which the crystal structure was reported of two small molecules,\u00a01,3-dimethyl cyclobutadiene\u00a0and\u00a0carbon dioxide, entrapped together inside a calixarene cavity. Other journals (e.g.\u00a0Nature Chemistry ran the article as a research highlight (where the purpose\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":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/11\/cbd.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":19194,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19194","url_meta":{"origin":28187,"position":5},"title":"Identification of a simplest hypervalent hydrogen fluoride anion.","author":"Henry Rzepa","date":"December 8, 2017","format":false,"excerpt":"An article with the title shown above in part recently appeared. Given the apparent similarity of HF1- to CH3F1- and CH3F2-, the latter of which I introduced on this blog previously,\u00a0I thought it of interest to apply my analysis to HF1-. The authors conclude that \"the F atom of HF\u2212\u2026","rel":"","context":"In "Hypervalency"","block_context":{"text":"Hypervalency","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=7"},"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\/28187","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=28187"}],"version-history":[{"count":40,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/28187\/revisions"}],"predecessor-version":[{"id":28238,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/28187\/revisions\/28238"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=28187"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=28187"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=28187"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=28187"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}