Alkyl: General Formula, Nomenclature, Classification of Carbon Atoms

Alkyl groups are formed by removing a hydrogen atom from an alkane molecule. Alkanes are often represented as R-H, where R is an alkyl group. The general formula for the alkyl group is CnH2n+1. The smallest alkyl group is CH3, which is called methyl. Cycloalkyl is derived from cycloalkanes by removing a hydrogen atom from the ring. The general formula for cycloalkyl is CnH2n-1.

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This Story also Contains

1. General Formula Of Alkyl Group
2. Nomenclature Of Alkyl Groups
3. Classification Of Carbon Atoms

Alkyl is a functional group in organic compounds, and it should be noted that all carbon-carbon (C-C) bonds are single bonds.

Alkyl groups are formed by cutting off a hydrogen atom from an alkane chain. One of the fundamental differences between alkyl groups and alkanes is that the latter are much more stable and less reactive, except that the former lacks a single hydrogen atom. Alkyl radicals have one unpaired electron on one of their carbons, making them unstable and highly reactive. Alkyl radicals are actually stabilised by resonance, which is the delocalization of electrons between bonded atoms. But they'd rather share a lone electron.

General Formula Of Alkyl Group

An alkyl group is an alkane that has lost one of its hydrogen atoms. They are formed by removing a hydrogen atom from the alkane structure. The general formula for alkanes is CnH2n+2, and to derive the general formula for alkyl groups, which is CnH2n+1, a single hydrogen atom must be removed from the formula.

This formula can be used to derive the corresponding alkyl of an alkane. It can also be used to write down the formula and structure of alkyl radicals, where 'n' is an integer value corresponding to the number of atoms.

The formula for an alkyl group with a structure containing 12 carbon atoms can be obtained by applying the following formula:

• Substitute the number of carbon atoms (12) for n.

• Solve the simple equation: C12H2(12 ) +1

The equation becomes C12H25.

Nomenclature Of Alkyl Groups

The IUPAC nomenclature is used for the nomenclature of alkyl groups. The basic idea of this system is to start by naming the longest chain of single-bonded hydrocarbons in a molecule. Several prefixes and suffixes must be used, all of which are already mandated by IUPAC.

The suffix for alkyl groups is -yl and the suffix for alkanes is -an, where -an simply replaces -yl in alkyl nomenclature. For example, the alkyl counterpart of butane is butyl, the counterpart of propane is propyl, and so on.

The position of the removed hydrogen atom determines the nomenclature prefix for alkyls with 3 or more carbon atoms. Propane is a good example. Hydrogen atoms can be removed from either the central C atom or the terminal C atoms.

When the central C atom loses a hydrogen atom, the alkyl group is called isopropyl.

When the hydrogen is removed from one of the terminal Cs, the alkyl group is called n-propyl. Here 'n' refers to regular or linear structure. To better understand the concept of naming, see the butane example:

• If one of the terminal carbons loses a hydrogen atom, the name becomes n-butyl.

• If the hydrogen is removed from the second C atom (here the alkane is symmetrical, so it doesn't matter if it comes from the left or right side), the name is sec-butyl, i.e., secondary carbon.

This is the case for the linear butane molecule, but if butane had a branched structure (isobutane):

If the hydrogen was removed from the central C, the name would be tert-butyl, tert- refers to tertiary.

• If one of the terminal C's loses a hydrogen atom, the name is isobutyl.

To master the nomenclature of alkyl groups, one must first review the classification of carbon atoms to identify the appropriate prefix to use.

Classification Of Carbon Atoms

In organic chemistry, carbon atoms can be classified into four main groups depending on their position in the alkane chain and the number of other carbons to which they are attached. These classes are:

1. Primary carbon atoms (-C-R): The carbon of interest is bonded to another carbon atom.

2. Secondary carbon atoms (-C-R2): The target carbon is bonded to two other carbon atoms.

3. Tertiary carbons (-C-R3): Here the carbon of interest is bonded to three other carbons.

4. Quaternary carbons (C-R4): Here the carbon of interest is attached to four carbons.