Functional Group

Organic chemistry is a universe of its own where different organic compounds are defined considering their structural features. One such feature that defines and classifies an organic compound is called functional groups. It is a group of atoms attached to a branch of other atoms that signify its organic nature. In this article, we will study these functional groups and how they are classified.

What is a Functional Group?

A group of atoms forming a component of a molecule that accounts for a particular function or chemical behavior is called a functional group. These moieties or sections can be found in different molecules. In fact, a moiety can identify a compound and introduce it into a particular genre or classification of similar compounds.

When we define a functional group, we imply a group of atoms of the same or different elements forming a chemically-active section of a compound and creating a class of new compounds. In organic chemistry, there are many such functional groups. For example, an alcohol group (-OH) defines a particular set of characteristics of the compounds that have it as a constituent. These characteristics will vary from one functional group to the other.

Even if a chemical compound is different from another one but has the same functional group, it will show the same chemical behavior. For instance, formic acid (H-COOH) and acetic acid (CH₃-COOH) show similar reactions in a chemical environment; they behave like organic acids due to the presence of the carboxyl (-COOH) group.

Classification of Functional Groups

Functional groups can be classified in the following ways.

• Hydrocarbons

This type of functional group contains only hydrogen and carbon as constituent elements. They are commonly represented with ‘R’. They are also called hydrocarbyl groups. The bonding between the carbon atoms can be single, double, or triple. The carbon and hydrogen bonds are always single.

These functional groups also vary in terms of reactivity due to the variation in the carbon chain length and the bonds between the constituent carbon atoms. They can be either branched or ringed. Some of these functional groups can contain a charge. Positively charged hydrocarbon groups are called carbocations and the negative ones are called carbanions.

• Haloalkanes

They are also called alkyl halides as the constituent elements are carbon, hydrogen, and halogens. The presence of a halogen adds a suffix according to the element. If it is fluorine then it is called fluoride. Similarly, if it is chlorine then it is called chloride.

The stability of the haloalkanes depends on the length and branches of the carbon atoms and the type and arrangements of the halogens present in the molecule. For instance, the bond between carbon and fluorine is stronger than that of carbon and chlorine.

• Functional Groups Containing Oxygen

The prime feature of this classification of functional groups is the presence of a carbon-oxygen bond in the arrangement. The type of bond entirely depends on its hybridization. It is explained using the electron donation effect of oxygen in the sp³ hybridization. This phenomenon can be witnessed in alcohol. On the other hand, the sp² hybridization and its withdrawing effect can be seen in any carbon-oxygen double bound (C=O).

There are other functional groups that contain atoms of other elements such as nitrogen, sulfur, phosphorus, etc.

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List of Functional Groups

Now that we have defined what a functional group in chemistry is, let us find out the types with proper examples.

• Alcohol (-OH)

The suffix of this functional group is -ol and the organic compound formed is called an alcohol. Example - Methyl alcohol or methanol.

• Aldehyde (-CHO)

In this functional group, a hydrogen and an oxygen atom are bonded with a carbon atom leaving another free bond to bind. The compounds have ‘al’ as a suffix. Example – ethanal or ethanaldehyde (CH₃CHO).

• Acyl Halide (-COX)

This functional group contains a halogen atom attached to the carbon atom. Its suffix is ‘oyl halide’. Example – ethanoyl halide (CH₃COCl).

• Ketone (=CO)

In this functional group, a carbon atom is attached to an oxygen atom with a double bond. The suffix is ‘one’. Example – acetone (CH₃COCH₃).

• Carboxyl (-COOH)

This functional group contains a carbon atom attached to an oxygen atom and a hydroxyl group. Its suffix is ‘oic’ in aid form and ‘oate’ in the ester or salt form. Example – ethanoic acid (CH₃COOH) and sodium ethanoate (CH₃COONa).

• Ester (-COO-)

This functional group is created when an organic acid reacts with alcohol. It is basically the organic version of an acid-base reaction where an organic salt is produced called an ester. Example – ethyl ethanoate (CH₃COOC₂H₅)

• Ether (-C-O-C-)

This functional group occurs when an oxygen atom is bonded to two carbon atoms on both sides. Its suffix is ‘alkyl ether’. Example – diethyl ether (CH₃ CH₂OCH₂ CH₃).

This is the classification and description of the common functional groups we study in organic chemistry. Every functional group has a different formula and a distinct suffix to be added to the nomenclature of the organic compounds. They also have specific functions that denote a particular class of organic compounds. Follow this article to understand what a functional group is and how it influences the behavior of a chemical compound.