Hydrogen Bonding to Alkanes: Computational Evidence

Abstract

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.

Intermolecular charge transfer as evidence for unusual O–H⋯C(sp3) hydrogen bond

“…In present article we consider the geometry and electronic structure of the HOH...CH 4 It should be added that previous results [75,124] obtained for complexes of water and hydronium with alkanes can be also considered as evidence of the OH...(CH) interactions. In adducts of hydronium with isobutane [124] and water with butane [75], the H atom points on the middle of CH bond, which is the region of high electron density associated with -electrons.…”

“…In adducts of hydronium with isobutane [124] and water with butane [75], the H atom points on the middle of CH bond, which is the region of high electron density associated with -electrons. Due to their ability to proton binding, CH  bonds are likely can participate in transport of protons in biochemical systems.…”

“…Earlier molecular complex formed by hydronium and methane was studied theoretically in the work of Olesen and Hummerum [124], in which the intermolecular interaction was defined as bifurcated dihydrogen bonding. However, Kryachko and Zeegers-Huyskens performed MP2/6-31+G(d,p) study [125] of the interaction between CH 4 and H 5 O 2 + in the complex of similar structure noted reasonably that "the nature of the intermolecular interaction in the present complex differs from that inherent for dihydrogen bondings", because "all three involved hydrogen atoms being positively charged, cannot act as an electron donor".…”

X-H⋯C hydrogen bonds in n-alkane-HX (X = F, OH) complexes are stronger than C-H⋯X hydrogen bonds

“…9 The proposed O-H· · · C hydrogen bond was observed to lie between a CH 3 group on a silicon surface and adsorbed H 2 O molecules. 26 Hammerum et al 27 recently considered alkanes as hydrogen bond acceptors with protonated alcohols/acids as donors.…”

Vibrational predissociation spectra of the Ar-tagged [CH4· H3O+] binary complex: spectroscopic signature of hydrogen bonding to an alkane

“…Results of electronic structure calculations [17] indicate that, in addition to the expected contributions from charge-induced dipole forces, the bonding between strong ionic acids (R 1 R 2 OH þ ) and alkanes involves a significant covalent component arising from the interaction between the à OH orbital of the proton donor and CH orbitals of the alkane. The latter contribution causes an elongation of both O-H and C-H bonds in addition to partial charge transfer between the constituents (0.065e derived from NBO analysis of the electron density distribution).…”