Unit 21: Amines
Nitrogen's lone pair makes it the course's most versatile base and nucleophile at once, from grabbing a stray proton to building a diazonium salt.
6 topics · 21 questions
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Amine Structure and Basicity
- How it worksHow does an amine's nitrogen lone pair sit available to grab a proton instead of being tied up in resonance like an amide's?
- Worked exampleFind which is more basic, aniline or cyclohexylamine, and explain the difference using the nitrogen lone pair's availability.
- Common mistakeWhy isn't an amide nitrogen basic the way an amine nitrogen is, even though both are nitrogen atoms with lone pairs?
- Going furtherWhat happens to an amine's basicity as more electron-withdrawing aromatic rings attach directly to its nitrogen?
Your turn1 of 2
The conjugate acid of an amine has a pKa (pKaH) of 9. In a solution at pH 7, what percent of the amine exists in its protonated, ammonium form? Use percent protonated = 100 / (1 + 10ph - pka).Amine Nomenclature and Nucleophilicity
- How it worksHow does an amine's available lone pair let it attack everything from alkyl halides to carbonyls to diazonium precursors?
- Worked exampleFind the correct name for a secondary amine formed from one methyl group and one ethyl group attached to nitrogen.
- Going furtherWhat happens to an amine's nucleophilicity once all three of nitrogen's hydrogens are replaced by bulky alkyl groups?
Your turn1 of 2
What is the correct name for a secondary amine formed from one methyl group and one ethyl group attached to nitrogen?Synthesis of Amines by Reductive Amination
- How it worksHow does a ketone condense with an amine to form an imine, which sodium cyanoborohydride then reduces to an amine?
- Worked exampleFind the amine product formed when cyclohexanone undergoes reductive amination with methylamine and sodium cyanoborohydride.
- Common mistakeWhy doesn't reductive amination require isolating and purifying the imine intermediate before the reduction step?
- Going furtherWhat happens to the product when ammonia, rather than a primary amine, is used as the nitrogen source in reductive amination?
Your turn1 of 2
Cyclohexanone undergoes reductive amination with methylamine and sodium cyanoborohydride. What is the amine product?Synthesis of Amines by the Gabriel Synthesis
- How it worksHow does phthalimide's deprotonated nitrogen perform a clean SN2 on an alkyl halide without over-alkylating the way ammonia would?
- Worked exampleFind the primary amine product formed when the Gabriel synthesis is run starting from 1-bromobutane.
- Ties togetherHow does the Gabriel synthesis solve the exact over-alkylation problem that comes up when ammonia reacts directly with a halide?
Your turn1 of 2
The Gabriel synthesis is run starting from 1-bromobutane. What is the primary amine product?The Hofmann Elimination
- How it worksHow does a bulky trimethylammonium leaving group force a base to grab the most accessible proton, giving the Hofmann product?
- Worked exampleFind the major alkene product when 2-aminobutane is exhaustively methylated, converted to its hydroxide, and heated.
- Common mistakeWhy doesn't the Hofmann elimination follow Zaitsev's rule the way an ordinary E2 on an alkyl halide would?
- Ties togetherHow does the Hofmann elimination's product selectivity connect back to the same steric argument behind bulky-base E2 eliminations?
Your turn1 of 2
2-aminobutane is exhaustively methylated to a quaternary ammonium salt, converted to its hydroxide, and heated. What is the major alkene product?Reactions of Amines with Nitrous Acid
- How it worksHow does nitrous acid convert an amine's nitrogen into a diazonium ion, and why does an aryl version of that ion survive while an alkyl one doesn't?
- Worked exampleFind the product when aniline is treated with nitrous acid at 0 degrees Celsius to form a diazonium salt.
- Going furtherWhat happens to an alkyl diazonium ion the moment it forms, given how unstable it is compared to an aryl one?
Your turn1 of 2
Aniline is treated with nitrous acid at 0 degrees Celsius. What forms?