In
chemistry, a C–H···O interaction is occasionally described as a special type of weak
hydrogen bond. These interactions frequently occur in the structures of important
biomolecules like
amino acids,
proteins, sugars, DNA and RNA.[1][2]
History
The C–H···O interaction was discovered in 1937 by
Samuel Glasstone. Glasstone studied properties of mixtures of
acetone with different
halogenated derivatives of
hydrocarbons 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.[3]
Properties
Similar to
hydrogen bonds, a C–H···O interaction involves
interactions of dipoles and therefore has
directionality.[4] 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.[5] Bond strength is less than 1 kcal/mol. In the case of
aromatic C–H donors, C–H···O interactions are not linear due to influence of
aromatic ring substituents near the interacting C-H group.[6][7] 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.[8]
^D. Ž.Veljković, G. V. Janjić, S. D. Zarić, "Are C–H···O interactions linear? Case of aromatic CH donors.", CrystEngComm, 2011, 13, 5005.
doi:
10.1039/C1CE05065F
^J. Lj. Dragelj, G. V. Janjić, D. Ž. Veljković and S. D. Zarić, "Crystallographic and ab initio Study of Pyridine CH/O Interactions. Linearity of the interactions and influence of pyridine classical hydrogen bonds", CrystEngComm, (2013), vol. 15, 10481. DOI: 10.1039/C3CE40759D
^K. Ramanathan, V. Shanthi, R. Sethumadhavan, Int J Pharm Pharm Sci, 2011, 3, 3, 324.
^D. P. Malenov, G. V. Janjić, D. Ž. Veljković, S. D. Zarić, "Mutual influence of parallel, CH/O, OH/π and lone pair/π interactions in water/benzene/water system", Computational and Theoretical Chemistry, (2013), vol. 1018, 59 - 65. DOI: 10.1016/j.comptc.2013.05.030
^D. Ž Veljković, V. B Medakovic, J. M. Andric and S. D. Zaric, "C–H/O interactions of nucleic bases with water molecule. Crystallographic and quantum chemical study.", CrystEngComm, 2014., DOI: 10.1039/C4CE00595C
^ 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