Carbon–carbon bond

A carbon-carbon bond is a covalent bond between two carbon atoms.^[1] The most common form is the single bond – a bond composed of two electrons, one from each of the two atoms. The carbon-carbon single bond is a sigma bond and is said to be formed between one hybridized orbital from each of the carbon atoms. In ethane, the orbitals are sp³ hybridized orbitals, but single bonds formed between carbon atoms with other hybridisations do occur (e.g. sp² to sp²). In fact, the carbon atoms in the single bond need not be of the same hybridisation. Carbon atoms can also form double bonds called alkenes or triple bonds called alkynes. A double bond is formed with an sp² hybridized orbital and a p-orbital that isn't involved in the hybridization. A triple bond is formed with an sp hybridized orbital and two p-orbitals from each atom. The use of the p-orbitals forms a pi bond.

Carbon has the unique characteristic among all elements to form long chains of its own atoms, a property called catenation. This coupled with the strength of the carbon-carbon bond gives rise to an enormous number of molecular forms, many of which are important structural elements of life, so carbon compounds have their own field of study: organic chemistry.

Branching is also common in C-C skeletons. Different carbon atoms can be identified with respect to the number of other carbon neighbors:

primary carbon atom: one carbon neighbor
secondary carbon atom: two carbon neighbors
tertiary carbon atom: three carbon neighbors
quaternary carbon atom: four carbon neighbors

primary, secondary, tertiary and quaternary carbon atoms

Synthesis

Carbon-carbon bond forming reactions are organic reactions in which a new carbon carbon bond is formed. They are important in the production of many man-made chemicals such as pharmaceuticals and plastics.

Some examples of reactions which form carbon-carbon bonds are Aldol reactions, Diels-Alder reaction, the addition of a Grignard reagent to a carbonyl group, a Heck reaction, a Michael reaction and a Wittig reaction.