https://doi.org/10.15255/KUI.2003.032
Published: Kem. Ind. 53 (11) (2004) 485–493
Paper reference number: KUI-32/2003
Paper type: Professional paper
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A Very Weak Hydrogen Bond: C–H···A

N. Raos and G. Pavlović

Abstract

Despite the fact that the C–H···O bond was discussed as early as 1936, proposing to be a possible explanation for the observed anomaly in the diethyl ether-chloroform solutions, its existence was not fully confirmed before the end of ’80. This very weak hydrogen bond (with energy tipically in the range 3 –10 kJ mol–1) was observed in halogenated akanes, besides alkenes, alkynes, and aromatic compounds. The hydrogen bond is formed even among methane and water molecules (E = 2.5 kJ mol–1). Besides oxygen, acceptors are N, Cl, or p , and hydrogen bonds with metals, C–H···M (M = Pt(II), Pd(II), were observed. The review deals with structural (X-ray and neutron analysis), spectroscopic (IR), and theoretical (quantum chemistry, molecular mechanics) studies of these weak hydrogen bonds. Special attention was paid to the role of C–H···O bonds in the stabilizing of the secondary protein structures (b -sheets) and to hydrogen bonds formed with three-membered rings, derived from cyclopropane, aziridine or oxirane. These compounds are especially interesting because three-membered rings can participate in hydrogen bonds both as donors and acceptors.

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Keywords

cyclopropane, halogenated hydrocarbons, proteins – secondary structure, hydrogen bonds with C–H donor, bifurcated hydrogen bonds, transition elements