Open AccessEffect of reaction exothermicity on the proton transfer chemical ionization mass spectra of isomeric C5 and C6 alkanols
Author(s) -
Jan A. Herman,
Alex G. Harrison
Publication year - 1981
Publication title -
canadian journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.323
H-Index - 68
eISSN - 1480-3291
pISSN - 0008-4042
DOI - 10.1139/v81-307
Subject(s) - chemistry , protonation , alkyl , ion , fragmentation (computing) , mass spectrum , proton affinity , chemical ionization , mass spectrometry , alkane , medicinal chemistry , ionization , electron ionization , alcohol , analytical chemistry (journal) , photochemistry , organic chemistry , catalysis , chromatography , computer science , operating system
The chemical ionization mass spectra of eight C 5 alkanols and fourteen C 6 alkanols have been obtained using H 3 + , N 2 H + , CO 2 H + , N 2 OH + , and HCO + as reactant ions. This choice of reactant ions allows the exothermicity of the protonation reaction to be varied from ∼90 kcal mol −1 (H 3 + ) to ∼50 kcal mol −1 (HCO + ). The major fragmentation reaction in all cases was H 2 O elimination from the protonated alcohol forming the appropriate C 5 H 11 + or C 6 H 13 + alkyl ion. The extent of further fragmentation of the alkyl ions decreased with decreasing exothermicity of the protonation reaction and was greatest for alkyl ions derived from primary alcohols, less for alkyl ions derived from secondary alcohols, and very small for alkyl ions derived from tertiary alcohols. The results indicate that there is negligible rearrangement to more stable alkyl ions prior to attaining the critical configuration which determines the energy partitioning between R + and H 2 O in the fragmentation of ROH 2 + . Other less important reaction modes in the CI spectra involved formation of (M – H) + ions and formation of oxycarbonium ions by alkane elimination from protonated alcohols.