Gas‐Phase Basicities of Open‐Chain and Cyclic Diols from Dissociations of Ammonium Adducts, Protonated Mixed Dimers and ICR Experiments. Structural and Stereochemical Effects

Abstract

Abstract The gas‐phase basicity (GB) of open‐chain and cyclic diols and triols has been determined by the method of dissociation of proton‐bound adducts using 1,4‐butanediol and cis ‐ and trans ‐1,3‐cyclohexanediol as reference compounds. The GB and proton affinity (PA) of the two cyclic reference diols have been obtained in ion‐cyclotron‐resonance experiments. The unimolecular and the collision‐activated dissociations of the ammonium adducts of the polyols allow a ranking of their GB and PA values which reflects the various structural and stereochemical effects. The possibility of internal H‐bonding between the two OH groups leads to a strong increase of the PA values. The incremental effect of chain length on the PA of open‐chain diols is evidenced, as well as the detailed influence of the configuration and conformation for cyclopentane‐ and cyclohexanediols, and ‐triols. These experiments also emphasized the predominant role of doubly H‐bound ammonium/diol chelate conformations as opposed to singly proton‐bound species.