The carbon-hydrogen bond (C–H bond) is a bond between carbon and hydrogen atoms that can be found in many organic compounds.1 Carbon–hydrogen bonds have a bond length of about 1.09 Å (1.09 × 10−10 m) and a bond energy of about 413 kJ/mol (see table below). Using Pauling's scale—C (2.55) and H (2.2)—the electronegativity difference between these two atoms is 0.35. Because of this small difference in electronegativities, the C−H bond is generally regarded as being non-polar. In structural formulas of molecules, the hydrogen atoms are often omitted. Compound classes consisting solely of C-H bonds and C–C bonds are alkanes, alkenes, alkynes, and aromatic hydrocarbons. Collectively they are known as hydrocarbons.
The C−H bond in general is unreactive. In several compound classes, collectively called carbon acids, the C−H bond can be sufficiently acidic for proton removal. Unactivated C−H bonds are found in alkanes and are not adjacent to a heteroatom (O, N, Si, etc.). Such bonds usually only participate in radical substitution. Another reaction type involving C−H bonds is so-called C−H bond activation mediated by metals and carbene C−H insertion. C–H bond oxidation suffers from lack of selectivity. Enzymes are known for selective oxidations and some organic procedures exist 2
Although the C−H bond is one of the strongest, it varies over 30% in magnitude for fairly stable organic compounds, even in the absence of heteroatoms.3
|Bond||Hydrocarbon radical||Bond dissociation energy (kcal/mole)|
The C−H unit is formally named carbogen.
|Core organic chemistry||Many uses in chemistry|
|Academic research, but no widespread use||Bond unknown|
- March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7
- Adding Aliphatic C–H Bond Oxidations to Synthesis M. Christina White Science 17 February 2012: Vol. 335 no. 6070 pp. 807–809 doi:10.1126/science.1207661