Abstract
Dependence of 1 J CH coupling on dielectric constant (ϵ ) has been studied in methylamine and methanol by 13C NMR measurement and by calculation with the FPT—INDO—Solvaton method. In methylamine the observed 1 J CH coupling decreases with increasing ϵ, but in methanol the observed 1 J Ch coupling increases with increasing ϵ. This result is reproduced in calculation. This is related to the fact that the calculated excitation energy of the former increases with increasing ϵ, but that of the latter decreases. Also, the effect of internal rotation on 1 j ch coupling is studied. It is found that when a lone pair of nitrogen or oxygen atom trans-orients against a C-H bond in a methyl group, the electrons are shifted to the C-H bond, resulting in a decrease of s character of the bond and the corresponding decrease in 1 j ch coupling.
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