Single and double hydrogen atom transfers in reactions (1) and (2) in the mass spectra of ethyl benzoate, isopropyl benzoate, and isobutyl benzoate have been investigated 6 t h reference to the orfbo effect: (1)
The formation of an [M + 1]+ ion and the fragmentation of isopropyl o‐toluate have been investigated by the deuterium labelling technique and kinetic energy release measurements. The hydrogen atom involved in the [M + 1]+ ion formation does not originate from a specific part of the molecule, but from all parts. A small amount of hydrogen exchange between the secondary carbon atom in the isopropyl group and the carbon atoms in the tolyl group takes place prior to decomposition of the molecular ion into the m/z 136 ion by a McLafferty rearrangement. Either almost complete scrambling of the hydroxyl hydrogen atom and the methyl hydrogen atoms in tolyl group or an almost equilibrated exchange of the hydroxyl hydrogen atom with one of the remaining hydrogen atoms in tolyl group also takes place prior to the elimination of a water molecule from the intermediate m/z 136 ion.
INTRODUCXIONBoth single and double hydrogen atom transfer reactions (1) and (2) paper, it has been reported4 from the m a s spectra of alkyl o-hydroxybenzoates (alkyl salicylates) and alkyl p-hydroxybenzoates that the intramolecular hydrogen bond' (interaction between the hydrogen atom in the hydroxyl group and the oxygen atom in the carboxyl group) may prevent the second hydrogen atom transfer.In the present paper, the temperature effect on the abundances of the rnlz 137 and mlz 136 ions generated by the reactions (2) and (1)
RESULTS AND DISCUSSIONIn the mass spectra of alkyl p-hydroxybenzoates, both rnlz 139 and rnlz 138 ions from reactions (2) and (1) were found? In contrast, only the single hydrogen atom transferred ion at mlz 138 was found in the spectra of alkyl salicylates, which have a hydroxyl group with a strong electron-donating property at the ortho p~s i t i o n .~In the case of toluic acid butyl esters, which have a methyl group with a weaker electron-donating property, the abundances of rearrangement ions caused by reactions (1) and (2) which occur at rnlz 136 and m/z 137 became quite intense. The mass spectra of the compounds studied are shown in Table 1
Single and double hydrogen atom transfers in reactions(1)and(2)are found in the mass spectra of n-propyl and n-butyl benzoates,and n-propyl and n-butyl p-hydroxy benzoates.In contrast,only single hydrogen atom transfer is found in the mass spectra of n-propyl and n-bulyl salicylates and it is concluded that the hydrogen bond prevents the second hydrogen atom transfer.The kinetic energy release for the loss of water from the m/z138ion[C7H6O3]+.produced from ethyl and higher alkyl salicylates by a McLafferty rearrangement was nearly equal to that from the molecular ion of salicylic acid(m/z138).The kinetic energy release for the loss of water from the m/z137 ion[C7H7NO2]+.from ethyl o-aminobenzoate was also equal to that from the molecular ion of o-amino benzoic acid(m/z137).However,the corresponding kinetic energy release from the m/z136ion[C8H8O2]+.from ethyl o-methylbenzoate was somewhat higher than that from the molecular ion of o-methyl benzoic acid(m/z136). Introaucuon Information about the structure of in termediate ion plays an important role in studying the structure of the molecular ion and the fragmentation mechanism of ions.The structure of common intermediate ions from different precursors has been mings Publishing Company.(1973),Chap.4. 22)H.M.Rosenstock and M.Krauss,in F.W. McLafferty(Ed.) •gMass Spectrometry of Organic Ions•h,Academic Press,New York, (1963),Chap.1.
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