question_answer

IUPAC name and degree of unsaturation of compound X is

A)  2, 3- dimethyl bicyclo [2,2,1] hept-5 ene,2

B)  T, 2- dimethyl bicyclo [2,2,1] hept-4 ene,3

C)  5, 6- dimethyl bicyclo [2,2,1] hept-2 ene,3

D)  4, 5- dimethyl bicyclo [2,2,1] hept-1 ene,2

Correct Answer: C

Solution :

 Idea This problem contains conceptual mixing of nomenclature of cyclic hydrocarbon and degree of unsaturation. This problem can be solved by identifying the parent chain, functional group, position of functional group, substituent and their position one by one and then write the name of compound according to IUPAC names then calculate degree of unsaturation. Total carbon atom forming the bicyclic ring =7 (hept.) Functional group => double bond (ene) Position of double bond\[\Rightarrow \]2, 2-ene Substituents\[\Rightarrow \]2-methyl group\[\Rightarrow \]dimethyl Position of substituents = 5, 6\[\xrightarrow{{}}\]5, 6-dimethyl Number of cyclic chain = 2\[\xrightarrow{{}}\]Bicycle 3-bridges are of 2 carbons, 2 carbons and one carbon hence. IUPAC name = 5, 6-dimethyl bicycio [2, 2, 1] hept 2-ene Molecular formula of compound is\[{{C}_{9}}{{H}_{14}}\]. Degree of unsaturation can be calculated as \[u=(C+1)-\frac{H}{2}+\frac{N}{2}\] where, u = degree of unsaturation C = number of carbons H = number of hydrogens N = number of nitrogen. Hence, for a compound having molecular formula\[{{C}_{9}}{{H}_{14}}\]the degree of unsaturation may be calculated as \[u=(9+1)-\frac{14}{2}\] \[=10-7=3\] TEST Edge JEE Main includes this type of question very frequently so students are advised to solve such problems as well as the problem including the nomenclature of spiro and biphenyl compound also.