A functional group is a group of atoms or bonds within a compound responsible for the way that compound behaves. In other words, functional groups are responsible for the characteristic chemical reactions of that compound. They play a vital role while naming the compounds (nomenclature) by combining the names of the functional groups with the names of the parent alkanes. The combination of one group with others provides a way to distinguish compounds. When numbering the long chain of atoms containing these atoms, it is recommended that you assign the lowest number to the carbon that has the function group. In a polyfunctional compound, the functional group(s) is considered as the principal group, and compounds are named considering other functional groups as substituent groups. The table below is meant to memorize the formulae, suffix and prefix of most common functional groups in the organic chemistry. Nevertheless, most common functional groups are alcohols (-OH), carboxylic acids (CO2H), carbonyls (C=O), esters (CO2R), and amines (NH2). In order to understand the physical and chemical properties of a given compound, it is very essential to form a functional group. In traditional nomenclature, the first carbon atom after the carbon that attaches to the functional group is called the alpha carbon; the second, beta carbon, the third, gamma carbon, etc. If there is another functional group at a carbon, it may be named with the Greek letter, e.g., the gamma-amine in gamma-aminobutyric acid is on the third carbon of the carbon chain attached to the carboxylic acid group.