Anisotropy of Bonds and Systems other than Aromatic

Anisotropy of bonds and systems (other than aromatic) 

Evidence has been adduced to show that the currently held views of the anisotropy associated with the carbonyl group (2) are incorrect, and that (3) is more correct (-t- indicates shielding, — denotes 

ApSimon and co-workers have modihed the McConnell equation to allow the calculation of the screening effects of C—C and C—H bonds at nuclei relatively close to them new values of the anisotropy constants for these bonds are given. A new treatment of the C=C bond by these workers takes account of the complete anisotropy of this bond (i.e., three magnetic susceptibilities must be used). The idea usually adopted for shielding cones of C=C bonds is rejected instead it is pointed out that deshielding of nuclei occurs only within a restricted region at the ends of the bonds, elsewhere nuclei either in or out of the plane of the double bond being shielded. Calculations based on these considerations are applied in the diterpene series. 

A neighbouring-group effect of an acetyl groups has been cited an equatorial proton adjacent to an axial tertiary OH group is shifted T1 p.p.m. downfield on acetylation of the latter. Shielding of the 

2-endo-CH. substituent is reported the high-held shift (relative 

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