Effects of stereoisomerism in the mass spectra of 2,4-disubstituted thiacyclohexanes
The mass spectra of cis- (Ia-c) and trans-2-methyl-4-R-thiacyclohexanes (IIa-c; a R = n-C4H9, b R = n-C5H11, c R = Ph) were studied. It was established that [M-CH3]+ ions, which correspond to the loss of a methyl group from the 2 position, are formed more readily in the case of the less stable trans isomers IIa-c than in the case of cis isomers Ia-c. The three-dimensional structures of the substances have no effect on the degree of elimination of the R substituent. The relative ionization energies (RIE) for Ia,b and IIa,b and the relative appearance energies (RAE) of the [M-CH3]+ ions were measured by the electron impact method. It was found that the RIE are almost 0.05 eV lower and that the RAE of the [M-CH3]+ ions are ∼0.1 eV lower for trans isomers IIa,b than for cis isomers Ia,b.