chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, a C–H···O interaction is occasionally described as a special type of weak

hydrogen bond In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

. These interactions frequently occur in the structures of important

biomolecule A biomolecule or biological molecule is loosely defined as a molecule produced by a living organism and essential to one or more typically biological processes. Biomolecules include large macromolecules such as proteins, carbohydrates, lipids ...

s like

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s, sugars, DNA and RNA.

History

The C–H···O interaction was discovered in 1937 by Samuel Glasstone. Glasstone studied properties of mixtures of

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

with different halogenated derivatives of

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...

s and realized that dipole moments of these mixtures differ from dipole moments of pure substances. He explained this by establishing the concept of C–H···O interactions. The first crystallographic analysis of C-H ⋯O hydrogen bonds were published by June Sutor in 1962.

Properties

Similar to hydrogen bonds, a C–H···O interaction involves interactions of dipoles and therefore has directionality. The directionality of a C–H···O interaction is usually defined by the angle ''α'' between the С, Н and О atoms, and the distance ''d'' between the O and C atoms. In a С–Н···О interaction, the angle ''α'' is in the range between 90 and 180°, and the distance ''d'' is usually smaller than 3.2 Å. Bond strength is less than 1 kcal/mol. In the case of

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

C–H donors, C–H···O interactions are not linear due to influence of aromatic ring substituents near the interacting C-H group. If aromatic molecules involved in С–Н···О interaction belong to the group of polycyclic aromatic hydrocarbons, the strength of C–H···O interactions increases with the number of aromatic rings. C–H···O interactions can be important in

drug design Drug design, often referred to as rational drug design or simply rational design, is the invention, inventive process of finding new medications based on the knowledge of a biological target. The drug is most commonly an organic compound, organi ...

, being present in structures of therapeutic proteins, and

nucleic acid Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nuclei ...

s. O-H···C and N-H···C type interactions could also play a significant role and were first analyzed in 1993. M.A. Viswamitra, R. Radhakrishnan, J. Bandekar, G. R. Desiraju, "Evidence for O-H···C and N-H···C hydrogen bonding in crystalline alkynes, alkenes, and aromatics", J. Am. Chem. Soc. 1993, 115, 4868-4869.DOI:10.1021/ja00064a055

References

{{DEFAULTSORT:C-H O interaction Organic chemistry