Question

The correct IUPAC name of the given compound is:





(A) isopropylbenzene
(B) cumene
(C) Phenyl iso-propene
(D) 2-phenyl propane

Answer 1

Hint: IUPAC refers to the International Union of Pure and Applied Chemistry. The nomenclature which follows the rules set up by this union is called IUPAC nomenclature and chemical compounds are named accordingly.

Complete step by step solution:
The complete IUPAC name of an organic compound consists of:
Secondary prefix + Primary prefix + Word root + Primary suffix + Secondary suffix
For example:
     





The compound given in the question is a simple aromatic compound. There are certain IUPAC rules that must be followed while naming the simple aromatic compounds:
-There are two types of aromatic compounds: (a) Nuclear substituted and (b) Side chain substituted. In nuclear substituted aromatic compounds, the functional group is directly attached to the benzene ring. Therefore they are named as derivatives of benzene. In side chain substituted aromatic compounds, the functional group is present in the side chain of the benzene ring and therefore they are named as the phenyl derivatives of the corresponding aliphatic compounds. The only exceptions are arenes.
-Arenes are hydrocarbons that contain both aliphatic and aromatic units. They are named as derivatives of benzene in the IUPAC system. Some of the examples are:






The compound given in the question is an arene since it contains a benzene ring attached to a propyl side chain. So, according to the IUPAC system it must be named as a derivative of benzene. This implies that the side chain has to be named as a secondary prefix.
Since the side chain contains 3 carbon atoms that are directly linked to each other in a straight chain, therefore it is a propyl group.
    




This propyl group is attached to the benzene ring through its carbon atom labelled as 2. Therefore this group will be named as Propan-2-yl. This Propan-2-yl group has to be written in brackets since this is a side chain. In the case of cyclic and aromatic compounds that are named as derivatives of their respective cyclic and benzene compounds, the side chains are written in parenthesis. Therefore the correct IUPAC name of the given compound is (Propan-2-yl)benzene. Such an option has not been given in the options provided. For certain compounds, their common name has been adopted as their IUPAC name also. For the given compound in question, the common name is isopropylbenzene that has also been adopted as its IUPAC name.
2-Phenyl propane is a common name of the given compound. ‘Phenyl iso-propene’ is wrong since this compound does not contain any double bond in the side chain. The suffix ‘ene’ in this denotes a double bond in the side chain.

Therefore the correct answer is (A) isopropylbenzene.

Note: This compound has multiple IUPAC names. Its IUPAC names include Cumene, (Propan-2-yl)benzene, (1-Methylethyl)benzene and isopropylbenzene. Always remember that there are some compounds for which their names have been accepted as their IUPAC name.