A tertiary carbon atom is a carbon atom bound to three other carbon atoms. For this reason, tertiary carbon atoms are found only in

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...

s containing at least four carbon atoms. They are called saturated hydrocarbons because they only contain carbon-carbon single bonds. Tertiary carbons have a hybridization of sp3. Tertiary carbon atoms can occur, for example, in branched alkanes, but not in linear alkanes. Tert-Butyl-Skeletal-SVG

Nomenclature

The R is the functional group attached to a tertiary carbon. If the functional group was an OH group, this compound would be commonly called ''tert-''butanol or ''t-''butanol. When a

functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...

is attached to a tertiary carbon, the prefix -''tert'' (-''t'') is used in the common name for the compound. An example of this is shown in the figure.

Significance

Carbocation Stability

Tertiary carbons form the most stable carbocations due to a combination of factors. The three alkyl groups on the tertiary carbon contribute to a strong inductive effect. This is because each alkyl group will share its

electron density Electron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial variables and is typical ...

with the central carbocation to stabilize it. Additionally, the surrounding sp3 hybridized carbons can stabilize the carbocation through hyperconjugation. This occurs when adjacent sp3 orbitals have a weak overlap with the vacant p orbital; since there are 3 surrounding carbons with sp3 hybridization, there are more opportunities for overlap, which contributes to increasing carbocation stability.

Reaction Mechanisms

A tertiary carbocation will maximize the rate of reaction for an

SN1 reaction The unimolecular nucleophilic substitution (SN1) reaction is a substitution reaction in organic chemistry. The Hughes-Ingold symbol of the mechanism expresses two properties—"SN" stands for "nucleophilic substitution", and the "1" says that th ...

by producing a stable carbocation. This happens because the rate determining step of a SN1 reaction is the formation of the carbocation. The rate of the reaction is therefore reliant on the stability of the carbocation because it means that the

transition state In chemistry, the transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. It is often marked w ...

has a lower energy level which makes the activation energy lower. Tertiary carbons are similarly preferred in E1 for the same reasons as it has a carbocation intermediate. E1 and E2 reactions follow Zaitsev's rule which states that the most substituted product in an elimination reactions is going to be the major product because it will be favored for its stability. This leads to tertiary carbons being preferred for their stability in elimination reactions. In general, SN2 reactions do not occur with tertiary carbons because of the steric hindrance produced by the substituted groups. However, recent research has shown there are exceptions to this rule; for the first time, a bimolecular nucleophilic substitution, aka

SN2 reaction The bimolecular nucleophilic substitution (SN2) is a type of reaction mechanism that is common in organic chemistry. In the SN2 reaction, a strong nucleophile forms a new bond to an sp3-hybridised carbon atom via a backside attack, all while t ...

, can happen to a tertiary carbon.Mascal, Mark; Hafezi, Nema; Toney, Michael D. (2010-08-11). "1,4,7-Trimethyloxatriquinane: S N 2 Reaction at Tertiary Carbon". ''Journal of the American Chemical Society''. 132 (31): 10662–10664. {{doi, 10.1021/ja103880c

ISSN An International Standard Serial Number (ISSN) is an eight-digit to uniquely identify a periodical publication (periodical), such as a magazine. The ISSN is especially helpful in distinguishing between serials with the same title. ISSNs a ...

0002-7863.

References

Chemical nomenclature Organic chemistry