Question

Names of some compounds are given. Which one is not correct in the IUPAC system?
A. \[C{H_3} - \mathop {\mathop C\limits_| }\limits_{OH} H - \mathop {\mathop C\limits_| }\limits_{C{H_3}} H - C{H_3}\]
3-Methyl-2-butanol
B. \[C{H_3} - C{H_2} \equiv C - CH{(C{H_3})_2}\]
4-methyl-2-pentyne
C. \[C{H_3} - C{H_2} - \mathop {\mathop C\limits_{||} }\limits_{C{H_2}} - \mathop {\mathop C\limits_| }\limits_{C{H_3}} H - C{H_3}\]
2-Ethyl-3-methyl-but-1-ene
D. \[C{H_3} - C{H_2} - C{H_2} - \mathop {\mathop C\limits_| }\limits_{C{H_2}C{H_3}} H - \mathop {\mathop C\limits^| }\limits^{C{H_3}} H - C{H_2}C{H_3}\]
3-Methyl-4-ethyl heptane

Answer 1

Hint:For the naming of compounds, first the parent chain is counted according to which the hydrocarbon is selected. The numbering is done from the higher priority group. The bonds present or functional groups present are written in suffix.

Complete step by step answer:
The International union of pure and applied chemistry has set some steps and rules which are involved in the naming of the chemical compound.
(A) \[C{H_3} - \mathop {\mathop C\limits_| }\limits_{OH} H - \mathop {\mathop C\limits_| }\limits_{C{H_3}} H - C{H_3}\]
In the given structure the parent chain contains 4 carbon atoms, so the hydrocarbon chain is butane. One methyl group is attached to the third carbon atom and one hydroxyl group is attached to the second carbon atom. As the alcohol group is present the suffix is given as –ol. Thus, the resulting IUPAC name is 3-Methyl-2-butanol.
Therefore, the given IUPAC name is correct.
(B) \[C{H_3} - C{H_2} \equiv C - CH{(C{H_3})_2}\]
In the given structure the parent chain contains 5 carbon atoms, so the hydrocarbon chain is pentane. One methyl group is attached to the fourth carbon atom and a second carbon atom triple bond is present. As triple bond is present the suffix is given as –yne. Thus, the resulting IUPAC name is 4-methyl-2-pentyne.
Therefore, the given IUPAC name is correct.
(3) \[C{H_3} - C{H_2} - \mathop {\mathop C\limits_{||} }\limits_{C{H_2}} - \mathop {\mathop C\limits_| }\limits_{C{H_3}} H - C{H_3}\]
In the given structure the parent chain contains 4 carbon atoms, so the hydrocarbon chain is butane. One methyl group is attached to the third carbon atom and one ethyl group is present in the second carbon atom. A double bond is present in the first carbon atom. As, double bond is present the suffix is given as –ene. Thus, the resulting IUPAC name is 2-Ethyl-3-methyl-but-1-ene.
Therefore, the given IUPAC name is correct.
(4) \[C{H_3} - C{H_2} - C{H_2} - \mathop {\mathop C\limits_| }\limits_{C{H_2}C{H_3}} H - \mathop {\mathop C\limits^| }\limits^{C{H_3}} H - C{H_2}C{H_3}\]
In the given structure the parent chain contains 7 carbon atoms, so the hydrocarbon chain is pentane. One methyl group is attached to the third carbon atom and one ethyl group is present in the fourth carbon atom. Thus, the resulting IUPAC name is 4-ethyl-3-Methyl-heptane.
Therefore, the given IUPAC name is incorrect.
Therefore, the correct option is D.

Note:
In option (D), The IUPAC naming is done according to rule where the substituents are written according to alphabetical order.