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IUPAC names of some compounds are given. Which one is incorrect -
A
$CH_3-CH_2-CH_2-CH(CH_2CH_3)-CH(CH_3)-CH_2CH_3$ : 3-Methyl-4-ethylheptane
B
$CH_3-CH(OH)-CH(CH_3)-CH_3$ : 3-Methyl-2-butanol
C
$CH_3-CH_2-C(=CH_2)-CH(CH_3)-CH_3$ : 2-Ethyl-3-methylbut-1-ene
D
$CH_3-C\equiv C-CH(CH_3)_2$ : 4-Methyl-2-pentyne
Detailed Solution
In IUPAC nomenclature, when two or more different substituents are present, their prefixes are written in alphabetical order, irrespective of their locants.
For $CH_3CH_2CH_2-CH(C_2H_5)-CH(CH_3)-CH_2CH_3$, the longest chain has seven carbons (heptane), with a methyl group on C-3 and an ethyl group on C-4.
Ethyl comes before methyl in alphabetical order, so the correct name is 4-ethyl-3-methylheptane, not 3-methyl-4-ethylheptane.
3-Methyl-2-butanol (3-methylbutan-2-ol) is correct: the OH group gets the lowest locant.
2-Ethyl-3-methylbut-1-ene is correct: the main chain must contain the double bond, and ethyl is cited before methyl.
4-Methyl-2-pentyne (4-methylpent-2-yne) is correct: the triple bond gets the lowest locant.
So the incorrect name is 3-methyl-4-ethylheptane.
For $CH_3CH_2CH_2-CH(C_2H_5)-CH(CH_3)-CH_2CH_3$, the longest chain has seven carbons (heptane), with a methyl group on C-3 and an ethyl group on C-4.
Ethyl comes before methyl in alphabetical order, so the correct name is 4-ethyl-3-methylheptane, not 3-methyl-4-ethylheptane.
3-Methyl-2-butanol (3-methylbutan-2-ol) is correct: the OH group gets the lowest locant.
2-Ethyl-3-methylbut-1-ene is correct: the main chain must contain the double bond, and ethyl is cited before methyl.
4-Methyl-2-pentyne (4-methylpent-2-yne) is correct: the triple bond gets the lowest locant.
So the incorrect name is 3-methyl-4-ethylheptane.