Question

How do IUPAC names differ from common names?

Answer 1

Hint: The chemical compounds are referred by their common name and most likely nowadays by their IUPAC name. The common name and the IUPAC name are the identity of the chemical compound but they differ from each other. Every chemical compound has more than one name.

Complete step by step answer:
The IUPAC nomenclature is the standardized name given to the organic compounds using official naming rules. Opposed to that, common names are older names given to the organic compounds, which are not official, but sometimes they are used. There is no explicit rule for writing the common names of the organic compound, and they are used interchangeably with IUPAC names, so one must get acquainted with both naming conventions terms.
An example showing the difference between common and IUPAC nomenclature is the chemical compound $C{H}_{3}COOH$. Using 'common' nomenclature, the chemical is named 'acetic acid'. However, under IUPAC nomenclature, the chemical is named 'ethanoic acid'.
The difference between the IUPAC names and the common names is shown below.

Common nomenclature	IUPAC nomenclature
No standardized rules are applied while naming the common name of the chemical compound.	The International Union of Pure and Applied Chemistry has some standardized rules to write the IUPAC name of the chemical compound.
In common name, the alkyl group is written first followed by the name of the functional group attached. Example: $C{H}_{3}C{H}_{2}OH$ Common name is ethyl alcohol.	In IUPAC nomenclature, the organic compounds are named after the parent hydrocarbon chain by using certain prefixes or suffixes to indicate the presence of a functional group. Example $C{H}_{3}C{H}_{2}OH$ IUPAC name is ethanol.
In common name, position of the substituent group is not written. The common name will be methylbutane.	The IUPAC name of a hydrocarbon is obtained by writing the position and name of the alkyl group or any other substituent group just before the name of the parent hydrocarbon. Example 2-methylbutane. Here the methyl group is present in the second carbon atom of butane.

Note: Both common name and the IUPAC name are asked for determining the chemical compound. But more likely IUPAC name is used as it is a standard name and applied while documentation and naming the chemicals.