Chemical ionization mass spectra of urethanes

Abstract

Chemical ionisation mass spectra using methane as the reagent gas are reported for 33 urethanes of general structure RNHCO₂C₂H₅[R = H, C_nH_2n+1(n= 1–8), CH₂CHCH₂, cyclo-C₆H₁₁, Ph, PhCH₂, PhCH₂CH₂, and Ph(CH₃)CH] and R₂NCO₂C₂H₅[R = C_nH_2n+1(n= 1–4)]. Abundant MH⁺ ions are present in all the spectra, accompanied by satellite peaks corresponding to [M+ C₂H₅]⁺ and [M+ C₃H₅]⁺. Four classes of fragment ions are of general importance in the spectra. Two of these, [MH – C₂H₄]⁺ and [MH – C₂H₅OH]⁺, are associated with the CO₂C₂H₅ group. The other two, corresponding to alkane and alkene elimination from MH⁺, arise from the RNH or R₂N function. The mechanisms whereby these fragment ions are formed are discussed and their analytical utility is illustrated by reference to the spectra of the four isomeric C₄H₉NHCO₂C₂H₅ and the eight isomeric C₅H₁₁NHCO₂C₂H₅ compounds. The results of ²H-labelling studies are presented and a comparison is made between the methane and ammonia chemical ionisation spectra of selected urethanes.