{"id":16601,"date":"2016-07-01T07:47:54","date_gmt":"2016-07-01T06:47:54","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=16601"},"modified":"2016-07-01T07:47:54","modified_gmt":"2016-07-01T06:47:54","slug":"anomeric-effects-at-boron-silicon-and-phosphorus","status":"publish","type":"post","link":"https:\/\/rzepa.net\/blog\/2016\/07\/01\/anomeric-effects-at-boron-silicon-and-phosphorus\/","title":{"rendered":"Anomeric effects at boron, silicon and phosphorus."},"content":{"rendered":"

\n\tThe anomeric effect occurs at 4-coordinate (sp3<\/sup>) carbon centres<\/a> carrying two oxygen substituents and involves an alignment of a lone electron pair on one oxygen with the adjacent C-O σ*-bond of the other oxygen. Here I explore whether other centres can exhibit the phenomenon. I start with 4-coordinate boron, using the crystal structure search definition below (along with R < 0.1, no disorder, no errors).[cite]10.14469\/hpc\/696[\/cite]\"anomeric-bo-sq\"\n<\/p>\n

\n\tThe result shows two prominent clusters, one with both torsion angles being 180°, and another with both being ~60°. This latter is the one that implies that there must be two lone pairs, one on each oxygen, that are anti-periplanar to the adjacent B-O bond. There are two more diffuse clusters where only one antiperiplanar alignment is seen. So yes, 4-coordinate boron can exhibit an anomeric effect!\n<\/p>\n

\n\t\"anomeric-bo\"This compares to the carbon-anomeric plot which is shown here for comparison, where the top right cluster of 180° torsions contains proportionately few hits than with boron.\n<\/p>\n

\n\t\"anomeric-co\"The next centre is at 4-coordinate silicon. Again three significant clusters are seen; one with two antiperiplanar lone pair alignments with Si-O bonds, and two more with just one such alignment. The previous hotspot for which both measured torsions were 180° is largely absent. So here, the anomeric effect is much stronger. Notice also that whereas the torsions in the region of 60° for the carbon centre lie along a ridge coincident with the diagonal  (bottom left to top right), that for the silicon centre show a ridge running orthogonal to the diagonal. An interesting point to follow up perhaps?\"anomeric-sio\"\n<\/p>\n

\n\tSince the off-diagonal clusters are relatively prominent, implying just one anomeric interaction, it is of interest to see if this results in any asymmetry in the two Si-O bond lengths. If its present, the effect is small.\n<\/p>\n

\n\t\"anomeric-sio-distances\"\n<\/p>\n

\n\tFinally 4-coordinate group 15 elements. Most of the hits are in fact for P; there are none for N. This shows four clusters; the two on the diagonal show respectively two and no antiperiplanar interactions. The two off-diagonal clusters show just one such orientation. As with  Si, the ridge in the 60° region run orthogonal to the diagonal.\n<\/p>\n

\n\t\"anomeric-gp15-o\"So this little exploration shows that the anomeric effect, best known for sugars and at a carbon centre, is in fact more general to the adjacent elements.\n<\/p>\n

\n\t <\/p>\n","protected":false},"excerpt":{"rendered":"

The anomeric effect occurs at 4-coordinate (sp3) carbon centres carrying two oxygen substituents and involves an alignment of a lone electron pair on one oxygen with the adjacent C-O σ*-bond of the other oxygen. Here I explore whether other centres can exhibit the phenomenon. I start with 4-coordinate boron, using the crystal structure search definition below […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[72,123,168,170,307,319,366,367,369,693,958,1928,2320],"class_list":["post-16601","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining","tag-acetals","tag-alkane-stereochemistry","tag-anomer","tag-anomeric-effect","tag-bond-length","tag-boron","tag-carbohydrate","tag-carbohydrate-chemistry","tag-carbohydrates","tag-crystal-structure-search-definition","tag-ester","tag-physical-organic-chemistry","tag-stereochemistry"],"_links":{"self":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/16601","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/comments?post=16601"}],"version-history":[{"count":0,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/16601\/revisions"}],"wp:attachment":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/media?parent=16601"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/categories?post=16601"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/tags?post=16601"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}