MHT-CET Chemistry · Teaching notes

Amines — MHT-CET Chemistry

Amines is about two questions a paper in MHT-CET Chemistry and rarely HARD — three of its past-year questions in eighty-three. It is a chapter of orders and named reactions: the aqueous basicity order that makes the secondary amine strongest and aniline weakest, the reductions that make amines (Mendius, LiAlH₄, Sn/HCl), the two Hofmann reactions that are always confused, the tests that sort primary from secondary from tertiary, and the diazonium salt with its replacement reactions and azo coupling. Five pages in the book's order. Every PYQ is tagged.

Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.

MHT-CET Chemistry strategy MHT-CET home

Subtopic notes

PYQ weightage by concept

10 concepts · 83 PYQs — where the marks actually sit, so you know what to drill first

Nomenclature and Classification of Amines19 PYQs · 23%

Concept	PYQs	Share
Primary, Secondary, Tertiary; Simple and Mixed; Aliphatic and Aromatic	12	14%
IUPAC Names, N-Prefixes and Counting C₄H₁₁N Isomers	7	8%

Physical Properties of Amines8 PYQs · 10%

Concept	PYQs	Share
N–H Hydrogen Bonding: Boiling Point and Solubility	8	10%

Preparation of Amines15 PYQs · 18%

Concept	PYQs	Share
Reductions: Nitrile, Amide and Nitro to Amine	10	12%
Hofmann Bromamide Degradation, Gabriel Synthesis and Ammonolysis	5	6%

Chemical Reactions and Basicity of Amines28 PYQs · 34%

Concept	PYQs	Share
Basicity: the Aqueous Order and pKb	14	17%
Exhaustive Methylation and Hofmann Elimination	8	10%
Acylation, the Carbylamine Test and Hinsberg's Reagent	6	7%

Diazonium Salts and Aromatic Amine Reactions13 PYQs · 16%

Concept	PYQs	Share
Diazotisation and the Replacement Reactions of the Diazonium Ion	10	12%
Azo Coupling: Diazonium Ion Plus Phenol or Aniline	3	4%

Formula & revision sheet

10 formulas · 10 gotchas across all subtopics — the exam-eve cheat-sheet

Nomenclature and Classification of Amines

Formulas (2)

Primary, Secondary, Tertiary; Simple and Mixed; Aliphatic and Aromatic · Degree of an amine $\text{RNH}_2\ (1^\circ),\quad \text{R}_2\text{NH}\ (2^\circ),\quad \text{R}_3\text{N}\ (3^\circ) \quad — \text{ count groups on N, not on C}$
IUPAC Names, N-Prefixes and Counting C₄H₁₁N Isomers · N-prefix naming $\text{longest chain on N} \to \text{alkan-}k\text{-amine};\quad \text{other N groups} \to N\text{-alkyl prefixes, alphabetical}$

Watch out for (2)

Grading the amine by its carbon
→ Primary, Secondary, Tertiary; Simple and Mixed; Aliphatic and Aromatic
Taking the ethyl as the parent chain
→ IUPAC Names, N-Prefixes and Counting C₄H₁₁N Isomers

Physical Properties of Amines

Formulas (1)

N–H Hydrogen Bonding: Boiling Point and Solubility · Two orders $\text{b.p.: } 1^\circ > 2^\circ > 3^\circ \text{ (isomers)};\quad \text{amine} < \text{alcohol} < \text{acid};\qquad \text{solubility: alcohol} > \text{amine} > \text{alkane}$

Watch out for (1)

Ranking amines above alcohols because N is 'more basic'
→ N–H Hydrogen Bonding: Boiling Point and Solubility

Preparation of Amines

Formulas (2)

Reductions: Nitrile, Amide and Nitro to Amine · Three reductions $\text{RCN} \xrightarrow{4[\text{H}]} \text{RCH}_2\text{NH}_2;\quad \text{RCONH}_2 \xrightarrow{\text{LiAlH}_4} \text{RCH}_2\text{NH}_2;\quad \text{RNO}_2 \xrightarrow{6[\text{H}]} \text{RNH}_2$
Hofmann Bromamide Degradation, Gabriel Synthesis and Ammonolysis · Hofmann bromamide degradation $\text{RCONH}_2 \xrightarrow{\text{Br}_2,\ \text{KOH (conc.)}} \text{RNH}_2 \quad (\text{one carbon fewer; } -28\ \text{g mol}^{-1})$

Watch out for (2)

Forgetting that cyanide adds a carbon
→ Reductions: Nitrile, Amide and Nitro to Amine
Losing CO₂ (44) instead of CO (28)
→ Hofmann Bromamide Degradation, Gabriel Synthesis and Ammonolysis

Chemical Reactions and Basicity of Amines

Formulas (3)

Basicity: the Aqueous Order and pKb · Aqueous basicity $\text{R}_2\text{NH} > \text{RNH}_2 \gtrless \text{R}_3\text{N} > \text{NH}_3 \gg \text{C}_6\text{H}_5\text{NH}_2;\qquad \text{low } pK_b = \text{strong base}$
Acylation, the Carbylamine Test and Hinsberg's Reagent · Carbylamine reaction $\text{R-NH}_2 + \text{CHCl}_3 + 3\text{KOH} \xrightarrow{\Delta} \text{R-N≡C} + 3\text{KCl} + 3\text{H}_2\text{O}$
Exhaustive Methylation and Hofmann Elimination · Hofmann elimination $\text{R}_3\text{N}^+\text{-CH}_2\text{CH}_3\ \text{OH}^- \xrightarrow{\Delta} \text{R}_3\text{N} + \text{CH}_2\text{=CH}_2 + \text{H}_2\text{O} \quad (\text{least substituted alkene})$

Watch out for (3)

Reading pKb as basic strength
→ Basicity: the Aqueous Order and pKb
Giving the carbylamine test to a secondary amine
→ Acylation, the Carbylamine Test and Hinsberg's Reagent
Eliminating the propyl group because it is 'bigger'
→ Exhaustive Methylation and Hofmann Elimination

Diazonium Salts and Aromatic Amine Reactions

Formulas (2)

Diazotisation and the Replacement Reactions of the Diazonium Ion · Diazotisation and hydrolysis $\text{ArNH}_2 \xrightarrow{\text{NaNO}_2/\text{HCl},\ 273\text{ K}} \text{ArN}_2^+\text{Cl}^- \xrightarrow{\text{H}_2\text{O},\ \Delta} \text{ArOH} + \text{N}_2 + \text{HCl}$
Azo Coupling: Diazonium Ion Plus Phenol or Aniline · Azo coupling $\text{ArN}_2^+ + \text{C}_6\text{H}_5\text{OH} \xrightarrow{\text{OH}^-} \text{Ar-N=N-C}_6\text{H}_4\text{-OH}\ (p)$

Watch out for (2)

Stopping at the diazonium salt
→ Diazotisation and the Replacement Reactions of the Diazonium Ion
Coupling in strong acid
→ Azo Coupling: Diazonium Ion Plus Phenol or Aniline