Electron impact studies. Part 116. Mechanism of keten elimination from acetanilide and phenyl acetate radical ions

Abstract

Ion cyclotron resonance studies show that the processes M⁺˙→(M – CH₂CO)⁺˙ from both the acetanilide and phenyl acetate molecular ions occur through four-membered transition states; the non-decomposing product ions from these processes correspond to the aniline and phenol ion radicals respectively.

Kinetic isotope effects (k_H/k_D) for H–D transfer from p-RC₆H₄·NH·CO·CH₂·D increase (from 1.5 to 2.2 for decompositions in the first field-free region) with increasing σ⁺ values of R. Kinetic energy releases occurring during the metastable decompositions M⁺˙→(M – CH₂CO)⁺˙ from p-RC₆H₄·NH·COMe increase with decreasing σ⁺. A similar study with p-substituted phenyl acetates shows k_H/k_D to be small (1.2–1.3) and insensitive to changes in the para-substituent. Kinetic energy release is also relatively insensitive to the nature of the substituent. These results are rationalised in terms of transition state geometries.