Metastable decompositions of gem‐dialkoxyalkanes upon electron impact. III. Diethoxymethane (CH2(OCH2CH3)2)

Abstract

Unimolecular metastable decomposition of diethoxymethane (CH2(OCH2CH3)2, 1) upon electron impact has been investigated by means of mass-analyzed ion kinetic energy (MIKE) spectrometry and theD-labeling technique in conjunction with thermochemistry. The m/z 103 ion ([M − H]+ : CH(OCH2CH3) = O+CH2CH3) decomposes into the m/z 47 ion (protonated formic acid, CH(OH) = O+H) by consecutive losses of two C2H4 molecules via an m/z 75 ion. The resulting product ion at m/z 47 further decomposes into the m/z 29 and 19 ions by losses of H2O and CO, respectively, via an 1,3-hydroxyl hydrogen transfer, accompanied by small kinetic energy release (KER) values of 1.3 and 18.8 meV, respectively. When these two elimination reactions are suppressed by a large isotope effect, however, another 1,1-H2O elimination with a large KER value (518 meV) is revealed. The m/z 89 ion ([M − CH3]+ : CH2(OCH2CH3)O+ = CH2) decomposes into the m/z 59 ion (CH3CH2O+ = CH2) by losing CH2O in the metastable time window. The source-generated m/z 59 ion ([M − OCH2CH3]+ : CH2 = O+CH2CH3) decomposes into the m/z 41 (CH2 = CH+CH2) and m/z 31 (CH2 = O+H) ions by losses of H2O and C2H4, respectively, with considerable hydrogen scrambling prior to decomposition. Copyright © 2000 John Wiley & Sons, Ltd.