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JEE Main levelSingle correct optionDifficulty 2 of 3g2068

Arrange in decreasing order of basic strength in the gas phase: $CH X_{3} NH X_{2}$ , $(CH X_{3}) X_{2} NH$ , $(CH X_{3}) X_{3} N$ .

A $(CH X_{3}) X_{3} N$ > $(CH X_{3}) X_{2} NH$ > $CH X_{3} NH X_{2}$
B $CH X_{3} NH X_{2}$ > $(CH X_{3}) X_{2} NH$ > $(CH X_{3}) X_{3} N$
C $(CH X_{3}) X_{2} NH$ > $(CH X_{3}) X_{3} N$ > $CH X_{3} NH X_{2}$
D $(CH X_{3}) X_{3} N$ > $CH X_{3} NH X_{2}$ > $(CH X_{3}) X_{2} NH$

Answer: A

In the gas phase there is no solvation, so only the

+ I

effect of the alkyl groups matters: each added methyl group stabilises the ammonium ion by polarisation, giving tertiary > secondary > primary.

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