A Correlation of Nuclear Magnetic Resonance Chemical Shifts in Pyramical Boron Compounds Using a Conical Ring Current Model

摘要

By adopting a classical free electron model for the pentagonal pyramidal systems CnB(6-n)H(10-n) (n = 0,1,2,3,4) and for the tetragonal pyramidal pentaborane and pentagonal bipyramidal 2,4-C2B5H7 it is possible to account for the relative chemical shifts of boron and terminal hydrogen atoms. Also a good correlation is obtained for alkyl protons in those methyl and ethyl derivatives for which spectra are available. In this approach the pyramidal framework is treated as a cone and one or more ring current loops are placed about the conical curved surface parallel to the base. The six 'delocalized' electrons bonding the apex to the base are treated in a manner similar to the ring current approach used for benzene. From the obtained correlations it is clear that this approach has considerable predictive value. (Author)