Question

The structure of 4-methyl pent-2-ene is:
(a) ${{(C{{H}_{3}})}_{2}}CH-C{{H}_{2}}-CH=C{{H}_{2}}$
(b) ${{(C{{H}_{3}})}_{2}}CH-CH=CH-C{{H}_{3}}$
(c) ${{(C{{H}_{3}})}_{2}}CH-C{{H}_{2}}-CH=CH-C{{H}_{3}}$
(d) ${{(C{{H}_{3}})}_{3}}C=CH-C{{H}_{2}}-C{{H}_{3}}$

Answer 1

Hint: As we know that the IUPAC nomenclature in organic chemistry is a method of naming various organic chemical compounds considering various rules as recommended by the International Union of Pure and Applied Chemistry (IUPAC). So here we tell the structure of a compound named as 4-methyl pent-2-ene.

Complete answer:
Let us understand few rules given by IUPAC which will be helpful in drawing the structure of this compound as follows:-
-If the compound is alkane, alkene or alkyne, then the suffix used for alkane is ‘ane’, alkene is ‘ene’ and alkyne is ‘yne’.
-On the basis of number of carbons present in chain, the prefixes used are:-

Number of carbons	Prefix used
1	Meth
2	Eth
3	Prop
4	But
5	Pent
6	Hex

 And so on.
-The numbering is done in the longest carbon chain which is considered as the parent chain and its name ends the nomenclature of that particular compound.
-The name of other minor chains or groups to the parent chain is written in the beginning.
-Numbering on the parent chain is done from higher priority groups to lower priority groups.
Now let us draw the structure of 4-methyl pent-2-ene as follows:-
-As pent-2-ene is given, which means there is a 5 member carbon chain as the parent chain along with the alkene at second position.
${{C}^{5}}{{H}_{3}}-{{C}^{4}}{{H}_{2}}-{{C}^{3}}H={{C}^{2}}H-{{C}^{1}}{{H}_{3}}$
-Next it says 4-methyl, which means there is a methyl substituent attached to the fourth carbon, hence the structure will be as follows:-
${{({{C}^{5}}{{H}_{3}})}_{2}}-{{C}^{4}}H-{{C}^{3}}H={{C}^{2}}H-{{C}^{1}}{{H}_{3}}$
-Hence the structure of 4-methyl pent-2-ene is (b) ${{(C{{H}_{3}})}_{2}}CH-CH=CH-C{{H}_{3}}$.

Note:
-If alkane groups are as minor substituents attached to the parent chain, then they are called as alkyl along with their position written in the beginning.
-Also alkenes are always given priority over alkynes and alkanes while numbering the parent chain.