Electron ionization and methane chemical ionization mass spectrometry study of some 2,2‐disubstituted 1,3‐dioxolanes, 1,3‐dithiolanes, 1,3‐oxathiolanes and 1,3‐dioxanes. Gas‐phase lactone and thiolactone formation

Abstract

AbstractThe electron ionization and methane chemical ionization mass spectra of some 2,2‐disubstituted 1,3‐dioxolanes, 1,3‐dithiolanes and 1,3‐oxathiolanes were studied. Especially, the effect of the length of the side chain in ring position 2 of these compounds and the ease of formation of possible lactone/thiolactone ion as a fragmentation product were examined. In addition, two 2,2‐disubstituted 1,3‐dioxanes were studied to see the effect of the bigger ring size. The formation of lactone ions was more favorable under methane chemical ionization than under electron ionization conditions. The structures of fragment ions and the ions generated from model compounds were carefully studied using both high‐ and low‐energy collision‐induced dissociation. Also ab initio molecular orbital calculations up to the HF/6–31G** level of theory for protonated 2‐methyl‐2‐propanoic acid ethyl ester of 1,3‐dioxolane, 1,3‐oxathiolane and 1,3‐dithiolane and for two isomeric bicyclic ions were carried out. The theoretical results obtained favor the formation of the lactone ion. Copyright © 2005 John Wiley & Sons, Ltd.