Amine basicity, nomenclature, and characteristic reactions of nitrogen-containing organic compounds tested on the MCAT.
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- What is a primary (1 degree) amine?
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An amine with nitrogen bonded to one carbon group and two hydrogens.- What is a secondary (2 degree) amine?
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An amine with nitrogen bonded to two carbon groups and one hydrogen.- What is a tertiary (3 degree) amine?
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An amine with nitrogen bonded to three carbon groups and no hydrogens.- What is a quaternary ammonium salt?
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A nitrogen bonded to four carbon groups, carrying a permanent positive charge.- Why are amines basic?
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The nitrogen has a lone pair of electrons that can accept a proton.- What is the approximate pKa of a protonated aliphatic amine (R-NH3+)?
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Around 10 to 11.- How does alkyl substitution on nitrogen affect amine basicity in the gas phase?
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It increases basicity, because alkyl groups donate electron density inductively and stabilize the positive charge on the protonated amine.- In aqueous solution, why do tertiary amines often not follow the gas-phase basicity trend?
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Steric hindrance and poor solvation of the bulky protonated ammonium ion reduce their basicity.- Is aniline more or less basic than cyclohexylamine?
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Less basic.- Why is aniline less basic than an aliphatic amine?
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The nitrogen lone pair delocalizes into the aromatic ring, making it less available to accept a proton.- How does an electron-withdrawing group like nitro on an aniline ring affect its basicity?
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It decreases basicity by pulling electron density away from the nitrogen lone pair.- How does an electron-donating group like methoxy on an aniline ring affect its basicity?
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It increases basicity by pushing electron density toward the nitrogen.- Are amides basic like amines?
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No, amides are only very weakly basic.- Why is the nitrogen lone pair in an amide much less available than in an amine?
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It is delocalized by resonance into the carbonyl group.- Why is pyridine basic?
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Its nitrogen lone pair sits in an sp2 orbital in the plane of the ring, not part of the aromatic pi system, so it is free to accept a proton.
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