NMR Spectrum of 1,1-Difluoroethylene in the Gas Phase

Abstract

The proton NMR spectrum of CH2CF2 in the gas phase consists of two sharp peaks and a number of broad features. The sharp peaks can be identified as transitions between states with the largest singlet fluorine spin character if the spin—rotation interaction is assumed to provide the dominant fluorine relaxation mechanism. Measurement of the splitting of the two sharp peaks as a function of pressure allows the association of the sharp lines in the gas-phase spectrum with the innermost pair of lines in the spectrum of liquid CH2CF2. This identification of the origin of the lines in an AA′XX′ spectrum removes the usual ambiguity in the relative sign of JAA′ and JXX′. In CH2CF2, JHH and JFF are opposite in sign.