A Product Rule for X–H Frequency Shifts

Abstract

DESPITE numerous studies of the infra-red spectroscopic changes which accompany interaction of an X–H group with a proton acceptor, no simple rule has been proposed relating the frequency shift Δv of the X–H fundamental to the nature of particular proton donors and acceptors. In recent studies involving the interaction of indole, pyrrole, N-methyl acetamide, diphenylamine and N-methyl aniline with a variety of compounds in carbon tetrachloride it became evident that the frequency shift could be expressed by a simple product rule: where D and A are constants characterizing the donor and acceptor, respectively, and Δv covers a range from 30 to 300 cm⁻¹. For this purpose a value was arbitrarily assigned to one donor, indole, and all constants related to this standard.