Carbon–hydrogen bond

The C−H bond is a bond between carbon and hydrogen atoms, most commonly found in 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 (2.5) and H (2.1)—the electronegativity difference between these two atoms is 0.4. 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.

Reactions

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.

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.^[2]

Nomenclature

The C−H unit is formally named carbogen.

See also

• Hydrocarbon

References