Ion-Neutral Complexes Resulting from Dissociative Protonation: Fragmentation of α-Furanylmethyl Benzyl Ethers and 4-N,N-dimethylbenzyl Benzyl Ethers

The loss of CH2O during mass spectrometry in two series of α-aromaticmethyl benzyl ether compounds, namely, α-furanylmethyl p-substituted-benzyl ethers and 4-N,N-dimethylbenzyl p-substituted-benzyl ethers, is particularly interesting. The fragmentation mechanism is proposed to involve an ion-neutral complex-mediated pathway. Specifically, before the formation of an ion-neutral intermediate, the proton is transferred from the thermodynamically favored site at either the ether oxygen atom or the nitrogen atom to the dissociative protonation site at Cα position in either the furyl group or the 4-N,N-dimethylphenyl group. This transfer has been clarified via computational studies and isotopically labeled experiments. In addition, the decomposition of the intermediate may be affected by the substituent groups on the phenyl ring. This conclusion is indicated by the reasonably good correlation between ln[([M + H − CH2O]+)/([M + H − CH2O − C6H5R]+)] and the substituent constants