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 N 2 is employed as an inert collision gas. The cis −1,2‐cyclopentanediol isomer favors H 2 O elimination to give predominantly [MH‐ H 2 O] + . In the trans isomer, where H 2 O elimination is less likely to occur, the rearrangement ion [HOCH 2 CHOH] + exists in significantly greater abundance. Ion‐molecule reactions with NH 3 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 [NH 4 ] + 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 + NH 4 ] + is of greater intensity for the trans isomer. In the proton transfer reaction with the cis isomer, the formation of [NH 4 ] + 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 .