Question

The IUPAC name of the compound is:

(A) $2$ - methyl - $2$ - butenoic acid
(B) $3$ - methyl - $3$ - butenoic acid
(C) $3$ -methyl but- $2$ - enoic acid
(D) $2$ - methyl - $3$ - butenoic acid

Answer 1

We will use the guidelines laid by the IUPAC (International Union of Pure and Applied Chemistry) to name the following chemical compound. IUPAC is an international chemistry union to which all the countries have agreed so that there are no two names for the same chemical compound. The longest chain will be the base compound with the substituents written as prefixes.

Complete step by step solution
In the above chemical compound, we can observe that there is a $COOH$ group as well as a double bond present. But $COOH$ is given more priority as compared to double bonds. So, we will start with $COOH$ as the first carbon atom and start identifying the longest carbon chain.
Then after identifying the longest carbon atom chain, we will start numbering the longest chain. The longest carbon chain consists of $4$ carbon atoms.
On the third carbon atom from the right-hand side, a $C{{H}_{3}}$ group is attached, so we number it as $3$ -methyl.
Also, we can observe that there is a double bond attached to the second carbon atom, and we have a total $4$ carbon atom in the chain, so we will name it as butane. But there is a double bond in the second position. So, its name will be rewritten as but- $2$ - ene.
Also, in the first position, there is the $COOH$ group. $COOH$ is an acid group, so the name will be but- $2$ -enoic acid.
Hence, the IUPAC name of the chemical compound is $3$ -methyl but- $2$ - enoic acid.
The correct option is (C).

Note
The need for such a systematic approach arose because of the sheer quantity of new organic compound discoveries that made the trivial nomenclature of organic compounds extremely inconvenient. However, chemists do not always follow the IUPAC nomenclature guidelines because some compounds, as per the IUPAC nomenclature guidelines, have very long and extremely tedious names. More trivial names are assigned to these compounds.