An encaged sigma* orbital in 3-methoxy-2,4,10-trioxaadamantane. Preferred exo-anomeric effect as revealed by the crystal structure

作者：Chandrasekhar Sosale^*; Mukherjee Somnath

来源：Journal of Molecular Structure, 2015, 1083: 426-429.

DOI：10.1016/j.molstruc.2014.10.077

• ALPH
• Antibonding orbital
• Antiperiplanar
• Charge transfer
• Donor-acceptor
• Stereoelectronic

In the titled tricyclic orthocarbonate derivative, the three endocyclic C-O bonds are longer than the exo-cyclic C-O bond (similar to 4.40 angstrom vs. similar to 1.37 angstrom). This indicates an anomeric-type interaction between the two electron lone pairs on the exocyclic oxygen atom and the antibonding orbitals of the two antiperiplanar endocyclic C-O bonds. The remaining endocyclic C-O bond - marginally shorter than the other two apparently adds to this effect. Intriguingly, the antibonding orbital of the exocyclic C-O bond extends into the interior of the adamantyl cage, and is stereoelectronically prevented from overlapping with any of the six adjacent lone pairs. The results also seem to indicate a preference for interaction between a single donor oxygen atom and multiple acceptor antibonding orbitals rather than vice versa. The results add insightfully to the substantial body of evidence favouring the antiperiplanar lone pair hypothesis (ALPH).

• 出版日期2015-3-5