Site of gas-phase ethyl ion attachment

The [C2D5]+ species forms an adduct in the gas phase with ethyl acetate, ethylbenzene, and p-ethyltoluene, which subsequently unimolecularly eliminates C2H4 and C2D4 in approximately a 2:1 ratio. These results indicate that the adduct is not a weakly bound ion–molecule complex but a bonded species in which the C2D5 group has become equivalent to the C2H5 group present in the molecule; the preference for elimination of C2H4 is due to an isotope effect. From observations of the relative loss of C2H4 and C2D4 from [C2D5]+ adducts with other molecules containing a C2H5 group, it is concluded that the [C2D5]+ species attaches to the carboxyl group in ethyl benzoate, primarily to the ring in substituted phenetoles and in ethylphenols, primarily to the nitrogen in ethylpyridines, and primarily to the ring for N-ethyl- and p-ethyl-aniline.