FORMATION OF CH3CH2OCH3+. AND .CH2+OHCH2CH3 FROM IONIZED 2-ETHOXYETHANOL AND THEORETICAL AND EXPERIMENTAL STUDIES OF THE REACTIONS OF .CH2+OHCH2CH3

It is concluded that C3H8O+. formed by dissociation of ionized 2-ethoxyethanol (8) is a mixture of CH3CH2OCH3+. (7) and .CH2+OHCH2CH3 (2). Formation of 7 and CH3CH2+OHCH3 (12) is attributed to dissociations of species formed by the hydrogen transfers [CH3CH2OCH2+.CH2OH] --> [CH3CH2OCH3+. CH2O] --> [CH3CH2+OHCH3 HCO.]. Production of 7 competes weakly with dissociation to CH3CH2+OCH2 (13) and to 12. The low abundance of 7 is attributed to the simple dissociation 8 --> 13 being both energetically and entropically favored, and a second H-transfer to give 12 being energetically favored. The threshold for forming 7 is 45 kJ mol-1 above that for dissociation directly to 13, so formation of 7 is the first ion-neutral complex-mediated elimination found to have a threshold above that for the competing simple dissociation. The low abundance of 7 also demonstrates that ion-neutral complexes an be intermediates without obviously revealing their presence by direct dissociation. Experimental results suggest that 2 isomerizes to CH3CH2CH2OH+. (5) and then dissociates hy eliminating water. Ab initio results support the feasibility of 2 --> CH3+OHCH2CH2 (1) and 2 --> 5. However, experimental observations suggest that 2 --> 1 does not occur. This is attributed to strong competition from dissociation and isomerization to 5. The transition state for 2 --> 5 resembles [CH3CH2 CH2OH]+. and a cyclic transition state for 2 --> 5 is ruled out. When the ethyl-oxygen bond in 2 is simply lengthened, the charge is initially concentrated on ethyl, but it switches to CH2OH in a curve crossing at an apparent transition state for C-O bond breaking.