question_answer 1)

Structures and IUPAC names of some hydrocarbons are given ahead. Explain why the names given in the parentheses are incorrect. (a) \[C{{H}_{3}}-\underset{\underset{\text{C}{{\text{H}}_{\text{3}}}}{\mathop{\text{ }\!\!|\!\!\text{ }}}\,}{\mathop{CH}}\,-C{{H}_{2}}-C{{H}_{2}}-\underset{\underset{\text{C}{{\text{H}}_{\text{3}}}}{\mathop{\text{ }\!\!|\!\!\text{ }}}\,}{\mathop{CH}}\,-\underset{\underset{\text{C}{{\text{H}}_{\text{3}}}}{\mathop{\text{ }\!\!|\!\!\text{ }}}\,}{\mathop{CH}}\,-C{{H}_{2}}-C{{H}_{3}}\] 2, 5, 6-Trimethyloctane (and not 3, 4, 7-Trimethyloctane)   (b) \[C{{H}_{3}}-C{{H}_{2}}-\underset{\underset{\text{C}{{\text{H}}_{\text{2}}}\text{C}{{\text{H}}_{\text{3}}}}{\mathop{\text{ }\!\!|\!\!\text{ }}}\,}{\mathop{CH}}\,-C{{H}_{2}}-\underset{\underset{\text{C}{{\text{H}}_{\text{3}}}}{\mathop{\text{ }\!\!|\!\!\text{ }}}\,}{\mathop{CH}}\,-C{{H}_{2}}-C{{H}_{3}}\] 3-Ethyl-5-methylheptane (and not 5-Ethyl-3-methyl heptane)  

Answer:

(a) The set of locants (2, 5, 6 = 13) is lower than the set of locants (3, 4, 7 = 14). (b) When substituents are at equivalent positions; lowest number is given to that substituent which comes first in alphabetical order.