Question

IUPAC name of the given compound is $C{H_3}$ - $C(C{H_3})H$ - $CH$ = $CH$- $C{H_2}$ -$COOH$ .

Answer 1

Hint: initially we should give numbering to the compound choosing the longest chain. By further using prefixes and suffixes, the parent name can be modified to obtain the actual name. The addition of the functional group present at the end of chain decides the suffix of the name.

Complete Step by step answer: There is a systematic procedure to write the IUPAC name. Rules for naming the compound are as following:
-First of all, the longest carbon chain in the molecule is identified.
-Then after this the carbon atoms of the parent chain are numbered to identify the parent alkane and to locate the positions of the carbon atoms at which branching takes place due to the substitution of the alkyl group in place of hydrogen atoms. The numbering is done in such a way that the branched carbon atoms get the lowest possible numbers.
-The names of alkyl groups attached as a branch are then prefixed to the name of the parent alkane and position of the substituents is indicated by the appropriate numbers. If different alkyl groups are present, they are listed in alphabetical order.
-If two or more identical substituent groups are present then the numbers are separated by commas. The names of identical substituents are not repeated, instead prefixes such as di (for 2), tri (for 3), and so on.
-If two substituents are found in equivalent positions, the lower number is given to the one coming first in the alphabetical listing.
-After that if the functional group is attached to it then first of all, the functional group present in the molecule is identified which determines the choice of appropriate suffix. The longest chain of the carbon atoms containing the functional group is numbered in such a way that the functional group is attached to the carbon atom possessing the lowest possible number in the chain.
-In case of the poly functional compounds, one of the functional groups is chosen as the principal functional group and the compound is named on that basis. The choice of principal functional group is made on the basis of order of preference.
-In this case the longest chain that is the parent chain is having 6 carbon atoms and a double bond as well. And functional group in this compound is carboxylic acid, for which suffix is –oic acid and prefix is carboxy. And also one methyl group is also attached to it. So as per rules name of the compound $C{H_3}$ - $C(C{H_3})H$ - $CH$ = $CH$- $C{H_2}$ - $COOH$ will be 5-methyl-hex-3-enoic acid.

Note: Always keep in mind that the numbering is done in such a way that the branched carbon atoms get the lowest possible numbers. And the parent chain will have the maximum number of carbon possible in the compound.