The structural, vibrational, and energetic properties of adducts of
alkanes and strong cationic proton donors were studied with composite ab
initio calculations. Hydrogen bonding in [D-H+ H-alkyl] adducts
contributes to a significant degree to the interactions between the two
components, which is substantiated by NBO and AIM results. The hydrogen
bonds manifest themselves in the same manner as conventional hydrogen
bonds, D-H bond elongation, D-H vibrational stretching frequency red shift
and intensity increase, and adduct stabilization. The alkane adducts
also exhibit elongation of the C-H bonds involved and a concurrent red
shift, which is rationalized in terms of charge-transfer interactions
that cause simultaneous weakening of both the O-H and C-H bonds. Like
other dihydrogen-bonded adducts, the adducts possess a bent structure
and asymmetric bifurcated hydrogen bonds. The hydrogen bonds are stronger
in adducts of isobutane and in adducts of stronger acids. Intramolecular
hydrogen bonding in protonated long-chain alcohols manifests itself in the
same manner as intermolecular hydrogen bonding and can be equally strong.
Udgivelsesdato: 12 juni 2009