Alkyl

An alkyl group is a saturated substituent consisting entirely of carbons and hydrogens. Its general formula is C_nH_2n+1.

P.S. Here is my 45-minute lesson on alkane nomenclature. Check it out! 

The Basics:

            There are several different alkyl groups, but there’s good news: they follow the same naming convention as alkanes but with one slight difference. For example, let’s say we’ve got a two-carbon chain. As a standalone molecule, we’d call that ethane. Eth indicates how many carbon atoms there are in the chain, and –ane specifies that it’s an alkane. As a substituent, however, it would be called ethyl. The –yl indicates that it’s a substituent of a larger molecule (or that it’s missing a hydrogen). 

Common Alkyl Groups:

            I’ve gone ahead and drawn methyl, ethyl, both propyls, and all butyls in bond line (skeletal structure) in blue below. I've also provided the condensed structures of the substituents. The cyclohexane just serves as a parent molecule :) Once we get into three-carbon substituents, we actually run into branched substituents:

Methyl, Ethyl, and Propyl:

Methylcyclohexane

The methyl substituent has just one primary carbon. Its condensed structure is —CH₃.

Ethylcyclohexane
The ethyl substituent has primary and secondary carbons. Its condensed structure is —CH₂CH₃.

Propylcyclohexane

The straight-chain propyl substituent has primary and secondary carbons. Its condensed structure is —CH₂CH₂CH₃.

Isopropylcyclohexane

The isopropyl substituent has primary, secondary, and tertiary carbons. Its condensed structure is —CH(CH₃)₂.

The Butyls:

N-Butyl

The straight-chain butyl has only primary and secondary carbons in it. Its condensed structure is —CH₂CH₂CH₂CH₃.

Isobutylcyclohexane

The isobutyl substituent has primary, secondary, and tertiary carbons in it. Its condensed structure is —CH₂CH(CH₃)₂.

Sec-butylcyclohexane

The sec-butyl substituent has primary, secondary, and tertiary carbons in it.  Its condensed structure is —CH(CH₃)CH₂CH₃

Tert-butylcyclohexane

The tert-butyl substituent has three primary carbons and one quaternary carbon. Its condensed structure is —C(CH₃)₃.

I hope this quick introduction helps! To see my videos explaining all of alkane nomenclature, including alkyl groups, click here. Good luck studying!