Question: Which of following is/are incorrect IUPAC names :...

Question

Which of following is/are incorrect IUPAC names :

Answer 1

Solution

Analysis of IUPAC Names:

Option (A): 1,6-Epoxy-1-ethyl-6-methyl hexane This name describes a cyclic ether. The term "1,6-Epoxy" indicates that an oxygen atom bridges the first and sixth carbon atoms of a hexane chain. This forms a 7-membered ring (6 carbons + 1 oxygen). According to IUPAC nomenclature, cyclic ethers are named based on the ring system. A 7-membered ring containing one oxygen atom is called an oxepane. The parent name "hexane" is incorrect for a cyclic structure. Therefore, "1,6-Epoxy-1-ethyl-6-methyl hexane" is an incorrect IUPAC name.
Option (B): 5-Hydroxy pentan-2-sulphonic acid The parent chain is a 5-carbon alkane (pentane). The principal functional group is sulphonic acid (-SO3H), which dictates the numbering of the parent chain to give it the lowest possible locant. If the sulphonic acid group is at position 2, the numbering is fixed. The hydroxy group (-OH) is located at position 5. The name follows the convention of listing substituents alphabetically before the parent name, with their locants. Thus, "5-Hydroxy pentan-2-sulphonic acid" is a correct IUPAC name.
Option (C): 2-Methyl cyclopent-4-en-1-ol The parent structure is a 5-membered ring (cyclopentane). The principal functional group is alcohol (-ol), which must be given the locant 1. Therefore, the carbon bearing the -OH group is C1. The double bond is indicated as "4-en", meaning it is located between C4 and C5. The methyl group (-CH3) is at position 2. The numbering starts from the carbon with the -OH group (C1), proceeds to give the lowest possible locants to the double bond and other substituents. Thus, "2-Methyl cyclopent-4-en-1-ol" is a correct IUPAC name.
Option (D): 4-(1,1-Dimethyl ethyl)-2-methyl pentane The parent chain is a 5-carbon alkane (pentane). The substituents are a methyl group (-CH3) and a 1,1-dimethylethyl group (tert-butyl group). We need to number the pentane chain to give the lowest locants to the substituents. Numbering from left to right: Methyl at C2, 1,1-Dimethylethyl at C4. Locant set: {2, 4}. Numbering from right to left: 1,1-Dimethylethyl at C2, Methyl at C4. Locant set: {2, 4}. Since the locant sets are the same, we apply the rule of alphabetical order of substituents. "1,1-Dimethylethyl" (D) comes alphabetically before "methyl" (M). Therefore, the numbering scheme that gives the lower locant to "1,1-Dimethylethyl" is preferred. Numbering from right to left gives "1,1-Dimethylethyl" the locant 2 and "methyl" the locant 4. The correct IUPAC name should be 2-(1,1-Dimethylethyl)-4-methyl pentane. The given name, "4-(1,1-Dimethyl ethyl)-2-methyl pentane", implies numbering from left to right, where methyl gets locant 2 and 1,1-dimethylethyl gets locant 4. This is incorrect because the alphabetically first substituent (1,1-dimethylethyl) does not have the lower locant. Therefore, "4-(1,1-Dimethyl ethyl)-2-methyl pentane" is an incorrect IUPAC name.

The incomplete part of the question text "all compounds of IUPAC name P-bromo-3-chloro-P₂-methyl pent-P-yne which can be cod according to IUPAC)." is disregarded.

Conclusion: The incorrect IUPAC names are (A) and (D).