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JEE Main levelSingle correct optionDifficulty 2 of 3nc023

Given that, in aqueous solution, the order of basicity of methylamines is , which pair correctly explains why trimethylamine is weaker than dimethylamine in water?

  1. Afewer N-H bonds in the cation, so less stabilisation by hydrogen bonding with water, together with steric hindrance
  2. Bthe +I effect of methyl is absent in trimethylamine
  3. Ctrimethylamine has less electron-donating methyl groups
  4. Dtrimethylamine has no lone pair

Answer: A

In water the conjugate acid is stabilised by hydrogen bonding through its N-H bonds. has only one N-H and is crowded, so solvation stabilisation falls and the strong +I effect of three methyls is outweighed. All methylamines have a lone pair and the same +I donors, so the other options are false.
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