Question

What is the IUPAC name of $C{H_3}CH = CH - COOH$?
A. 2-Butenoic acid
B. Crotonic acid
C. 2-Butanoic acid
D. 3-Butenoic acid

Answer 1

We need to study the given compound based on IUPAC rules for naming compounds. Different IUPAC names are assigned to organic compounds based on a set of rules. IUPAC is a universally recognized system for chemical nomenclature and terminology. It gives us a uniform and consistent nomenclature and terminology for organic compounds. The system names compounds on the basis of the number of carbon atoms, presence of functional groups, type of bonding between carbon atoms and on various other factors.

Complete answer:
The basic set of rules to be followed while naming any compound under the IUPAC system are as follows:
1. Predict whether the given compound is saturated or unsaturated: Saturation and unsaturation depends on the type of bonding between carbons. Saturated compounds contain carbons connected by single bonds only and unsaturated compounds contain double or triple bonds. Alkanes being the roots for naming organic compounds are a family of saturated hydrocarbons and hence they have the suffix “-ane”. In case of unsaturated hydrocarbons, the suffix “-ene” is used for compounds having double bonds and “-yne” for triple bonds.
2. Locate the longest continuous carbon chain which is the parent chain: Depending on the number of carbons in the parent chain, the alkanes are names as methane (one carbon parent chain), ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane (ten carbon parent chain).
3. Locate the functional groups: The functional groups are carboxylic acid $\left( { - COOH} \right)$, aldehyde $\left( { - CHO} \right)$, ketone $\left( { - CO} \right)$, alcohol $\left( { - OH} \right)$ and amine $\left( { - N{H_2}} \right)$. Based on the functional groups, different prefixes and suffixes are given to the names.
Keeping the following rules in mind, the given compound is numbered and is named But−2−ene−1−oicacid.

So, the correct answer is “Option A”.

Note:
We must note that the rules for naming organic compounds are complex and long data depending on the type of organic compound. Using these above IUPAC rules, the chemical formula can be detected for a given IUPAC name. These include only the basic rules. Some complicated rules for molecules containing various substituents should also be studied.