{"id":24045,"date":"2021-07-22T08:30:51","date_gmt":"2021-07-22T07:30:51","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=24045"},"modified":"2021-07-22T08:30:51","modified_gmt":"2021-07-22T07:30:51","slug":"another-very-large-anomeric-effect-with-a-twist","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=24045","title":{"rendered":"Another very large anomeric effect – with a twist."},"content":{"rendered":"
\n

In the earlier post on the topic of anomeric effects, I identified <\/a>a number of outliers associated with large differences in the lengths of two carbon-oxygen bonds sharing a common carbon atom.<\/p>\n

\"\"<\/p>\n

Here is another of these outliers (MUZZIS[1]<\/a><\/span>) which shows equally unusual properties. This is an oxyanion (counterion is trimethylbenzylammonium) which is part of a very strong O-H-O hydrogen bond in which the\u00a0O…O distance is\u00a02.44\u00c5 and the O-H distances are each indicated as 1.23\u00c5, suggesting the hydrogen is symmetrically disposed about the two oxygens. The anomerically lengthened C-O bonds (shown in red below) are\u00a01.513\/1.516\u00c5, which is indeed long for a\u00a0C-O bond.<\/p>\n

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

A \u03c9B97XD\/Def2-SVPP\/SCRF=chloroform calculation reveals a less symmetrical hydrogen bonding system, with calculated\u00a0O-H distances of 1.046\/1.434 (mean 1.24\u00c5) and an O-O distance of 2.48\u00c5. The anomerically lengthened C-O distances are 1.479\/1.582\u00c5. There are several reasons for these differences:<\/p>\n

    \n
  1. The temperature at which the X-ray data were recorded was 173K and it remains possible that the data represent an averaged position for the atoms at this temperature rather than a truly symmetrical hydrogen bond.<\/li>\n
  2. The basis set\/DFT method for the calculation may itself favour unsymmetrical hydrogen bonds.<\/li>\n<\/ol>\n

    The two\u00a0NBO energy perturbation terms<\/a> for one lone pair on the oxygens interacting with the empty C-O\u00a0\u03c3* orbital are 31.6 and 57.5 kcal\/mol. If the hydrogen bond is in reality entirely symmetric, then the NBO term would be expected to be approximately the average of these two values.<\/p>\n

    \"\"

    Click image to obtain 3D model<\/p><\/div>\n

    The earlier record anomeric holder<\/a> achieved this by virtue of charge relocation involving an oxenium cation rather than the normal effect of charge separation. Here we have a similar effect, this time involving oxy-anionic charge relocation. Both are therefore special cases.<\/p>\n

    References<\/h2>\n
    1. R. Bengiat, M. Gil, A. Klein, B. Bogoslavsky, S. Cohen, and J. Almog, \"Bis(benzyltrimethylammonium) bis[(4<i>SR<\/i>,12<i>SR<\/i>,18<i>RS<\/i>,26<i>RS<\/i>)-4,18,26-trihydroxy-12-oxido-13,17-dioxaheptacyclo[14.10.0.0<sup>3,14<\/sup>.0<sup>4,12<\/sup>.0<sup>6,11<\/sup>.0<sup>18,26<\/sup>.0<sup>19,24<\/sup>]hexacosa-1,3(14),6,8,10,15,19,21,23-nonaene-5,25-dione] sesquihydrate: dimeric structure formation<i>via<\/i>[O\u2014H\u2014O]<sup>\u2212<\/sup><i>negative charge-assisted hydrogen bonds (\u2013CAHB)<\/i>with benzyltrimethylammonium counter-ions\", Acta Crystallographica Section E Crystallographic Communications<\/i>, vol. 72, pp. 399-402, 2016. https:\/\/doi.org\/10.1107\/s2056989016002899<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

      In the earlier post on the topic of anomeric effects, I identified a number of outliers associated with large differences in the lengths of two carbon-oxygen bonds sharing a common carbon atom. Here is another of these outliers (MUZZIS) which shows equally unusual properties. This is an oxyanion (counterion is trimethylbenzylammonium) which is part of […]<\/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,"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":[1754],"tags":[],"class_list":["post-24045","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-6fP","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/24045","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=24045"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/24045\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=24045"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=24045"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=24045"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}