In chemistry, the carbonâÂÂhydrogen bond ( bond) is a chemical bond between carbon and hydrogen atoms that can be found in many organic compounds. This bond is a covalent, single bond, meaning that carbon shares its outer valence electrons with up to four hydrogens. This completes both of their outer shells, making them stable.
CarbonâÂÂhydrogen bonds have a bond length of about 1.09 à(1.09 à10<sup>âÂÂ10</sup> m) and a bond energy of about 413 kJ/mol (see table below). Using Pauling's scaleâÂÂC (2.55) and H (2.2)âÂÂthe electronegativity difference between these two atoms is 0.35. Because of this small difference in electronegativities, the bond is generally regarded as being non-polar. In structural formulas of molecules, the hydrogen atoms are often omitted. Compound classes consisting solely of bonds and bonds are alkanes, alkenes, alkynes, and aromatic hydrocarbons. Collectively they are known as hydrocarbons.
In October 2016, astronomers reported that the very basic chemical ingredients of lifeâÂÂthe carbonâÂÂhydrogen molecule (CH, or methylidyne radical), the carbonâÂÂhydrogen positive ion () and the carbon ion ()âÂÂare created, in large part, using energy from the ultraviolet light of nearby stars, rather than in other ways, such as turbulent events related to supernovae and young stars, as thought earlier.
The length of the carbonhydrogen bond varies slightly with the hybridisation of the carbon atom. A bond between a hydrogen atom and an sp<sup>2</sup> hybridised carbon atom is about 0.6% shorter than between hydrogen and sp<sup>3</sup> hybridised carbon. A bond between hydrogen and sp hybridised carbon is shorter still, about 3% shorter than sp<sup>3</sup> CâÂÂH. This trend is illustrated by the molecular geometry of ethane, ethylene and acetylene.
The CâÂÂH bond in general is very strong, so it is relatively unreactive. In several compound classes, collectively called carbon acids, the CâÂÂH bond can be sufficiently acidic for proton removal. Unactivated CâÂÂH bonds are found in alkanes and are not adjacent to a heteroatom (O, N, Si, etc.). Such bonds usually only participate in radical substitution. Many enzymes are known, however, to effect these reactions.
Although the CâÂÂH bond is one of the strongest, it varies over 30% in magnitude for fairly stable organic compounds, even in the absence of heteroatoms.