ISOMERIZATION REACTION OF [C6H6 C4H9+] PI-COMPLEXES

Metastable protonated butylbenzenes have been studied by extensive labelling and kinetic energy release measurements. Protonated s-butylbenzene isomerizes by 1-2 hydrogen shift to the pi-complex [C6H6 s-C4H9+], and the s-C4H9+ cation rearranges to t-C4H9+. The interconversion between [C6H6 s-C4H9+] and [C6H7+ C4H8] ion/neutral complexes is demonstrated. Protonated t-butylbenzene reacts without hydrogen exchange to give t-C4H9+, while protonated n-butylbenzene isomerizes to s-butylbenzene prior to dissociation. Protonated iso-butylbenzene isomerizes to protonated t-butylbenzene and to protonated s-butylbenzene. In the 2nd field-free region, the dissociation of this last form predominates.