Gas-phase basicities of open-chain and cyclic diols from dissociations of ammonium adducts, protonated mixed dimers and ICR experiments: structural and stereochemical effects

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.

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