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] → [CH3CH2OCH2OCH3+˙ CH2O] → [CH3CH2+OHCH3HCO˙]. 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 can be intermediates without obviously revealing their presence by direct dissociation. Experimental results suggest that 2 isomerizes to CH3CH2CH2OH+˙ (5) and then dissociates by 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 [CH3CH2CH2OH]+˙, 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 CO bond breaking.
ASJC Scopus subject areas
- Molecular Medicine