REACTIVE COLLISIONS IN QUADRUPOLE CELLS .6. H D EXCHANGE-REACTIONS OFPROTONATED ALKYLBENZENES WITH D2O,CH3OD, AND C2H5OD/

The H/D exchange reactions occurring on collision of protonated alkylb enzenes with C2H5OD, CH3OD, and D2O at low collision energies in the q uadrupole collision cell of a hybrid tandem mass spectrometer have bee n studied for 22 alkylbenzenes. The exchange reactions with D2O are mu ch less efficient than the exchange reactions with C2H5OD or CH3OD; th is difference is rationalized on energetics grounds. The H/D exchange of the protonated alkylbenzenes with C2H5OD or CH3OD leads, typically, to 40-70% deuterium incorporation in the protonated alkylbenzene and, for most cases, to significant ion signals corresponding to exchange of the added hydrogen and the aromatic hydrogens. Thus, the method is a feasible approach to counting the number of aromatic hydrogens in al kylbenzenes. The extent of exchange decreases with increasing size of the alkyl group in monoalkylbenzenes for reasons that are not readily understood.