JEE Main 2026 Apr 5 Shift 2, Chemistry Q14: Naming of Alkanes

JEE Main2026Apr 5, Shift 2Chemistry

Identify the correct IUPAC name of hydrocarbon (X) containing three primary carbon atoms and with molar mass 72 g mol $^{- 1}$ .

Solution

Molar mass 72 g/mol corresponds to $C_{5} H_{12}$ (saturated, formula $C_{n} H_{2 n + 2}$ ).

Count primary carbons (carbons attached to exactly one other carbon) in each candidate:

n-pentane $C H_{3} C H_{2} C H_{2} C H_{2} C H_{3}$ : 2 primary C.

2-methylbutane $(C H_{3})_{2} C H C H_{2} C H_{3}$ : 3 primary C.

2,2-dimethylpropane $(C H_{3})_{4} C$ : 4 primary C.

$∴$ The answer is 2-methylbutane.

Concept behind this question

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