Differentiation of the isomeric 1,2-cyclopentanediols by ion-molecule reactions in a triple-quadrupole mass spectrometer

Collisionally activated decompositions and ion-molecule reactions in a triple-quadrupole mass spectrometer are used to distinguish between cis- and trans-1,2-cyclopentanediol isomers. For ion kinetic energies varying from 5 eV to 15 eV (laboratory frame of reference), qualitative differences in the daughter ion spectra of MH]⁺ are seen when N₂ is employed as an inert collision gas. The cis ?1,2-cyclopentanediol isomer favors H₂O elimination to give predominantly MH- H₂O]⁺. In the trans isomer, where H₂O elimination is less likely to occur, the rearrangement ion HOCH₂CHOH]⁺ exists in significantly greater abundance. Ion-molecule reactions with NH₃ under single-collision conditions and low ion kinetic energies can provide thermochemical as well as stereochemical information. For trans ?1,2-cyclopentanediol, the formation of NH₄]⁺ by proton transfer is an exothermic reaction with the maximum product ion intensity at ion kinetic energies approaching 0 eV. The ammonium adduct ion M + NH₄]⁺ is of greater intensity for the trans isomer. In the proton transfer reaction with the cis isomer, the formation of NH₄]⁺ is an endothermic process with a definite translational energy onset. From this measured threshold ion kinetic energy, the proton affinity of cis ?1,2-cyclopentanedioi was estimated to be 886 ± 10 kJ mol^?1.