Formation of CH₃CH₂OCH₃^+˙ and ^˙CH₂⁺OHCH₂CH₃ from ionized 2‐ethoxyethanol and theoretical and experimental studies of the reactions of ^˙CH₂⁺OHCH₂CH₃

Abstract

Abstract It is concluded that C 3 H 8 O +˙ formed by dissociation of ionized 2‐ethoxyethanol (8) is a mixture of CH 3 CH 2 OCH 3 +˙ (7) and ˙ CH 2 + OHCH 2 CH 3 (2). Formation of 7 and CH 3 CH 2 + OHCH 3 (12) is attributed to dissociations of species formed by the hydrogen transfers [CH 3 CH 2 OCH 2 + ˙ CH 2 OH] → [CH 3 CH 2 OCH 2 OCH 3 +˙ CH 2 O] → [CH 3 CH 2 + OHCH 3 HCO ˙ ]. Production of 7 competes weakly with dissociation to CH 3 CH 2 + OCH 2 (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 CH 3 CH 2 CH 2 OH +˙ (5) and then dissociates by eliminating water. Ab initio results support the feasibility of 2 → CH 3 + OHCH 2 CH 2 ˙ (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 [CH 3 CH 2 CH 2 OH] +˙ , 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 CH 2 OH in a curve crossing at an apparent transition state for CO bond breaking.