The structure of an alkyl is like that of its alkane counterpart, but with one less hydrogen atom. For example, this is the structure of methyl, the smallest alkyl:
A secondary alkyl group is branched with the central carbon atom linked to two carbon residues. Likewise, in tertiary alkyl groups, there are three carbon-linked substituents. In neopentane, the central carbon atom is quaternary.
An example of a reaction in which alkyls are formed instantly is chlorination. This reaction involves chlorine free radicals, formed by photodissociation, reacting with an organic molecule, usually an alkane. The chlorine free radical will bond with a hydrogen from an alkane, forming hydrochloric acid and leaving an alkyl. This alkyl will then bond to a chlorine to form the product, a chloroalkane. The reaction is very energetic and can be explosive if proper precautions are not taken. This is because of the reactivity of free radicals.
|Number of carbons||1||2||3||4||5||6||7||8||9||10||11||12|
The structure of 3-methylpentane consists of two parts. First, the longest straight chain of carbon atoms, 5 carbons long with all single bonds, which is named pentane (highlighted blue). Second, there is an alkyl group, which is one carbon long, which is methyl (highlighted red). Alkyl groups are included in the name of the molecule before the root, as in methylpentane. This name is, however, ambiguous, as the methyl branch could be on various carbon atoms. Thus, the name is 3-methylpentane to avoid ambiguity: The 3- is because the methyl is attached to the third of the 5-carbon atoms.
If there is more than one of the same alkyl group attached to a chain, then the prefixes are used on the alkyl groups to indicate multiples (i.e., di, tri, tetra, etc.)
This compound is known as 2,3,3-trimethylpentane. Here, there are three identical alkyl groups attached to carbon atoms 2, 3, and 3. These numbers are included in the name to avoid ambiguity on the position of the groups, and 'tri' indicates that there are three identical methyl groups. If one of the methyl attached to the third carbon atom were an ethyl group, then the name would become 3-ethyl-2,3-dimethylpentane. Note that, when there are different alkyl groups, they are listed in alphabetical order.