Organic Compounds Containing Nitrogen

Definition

Amines are organic compounds that can be considered as derivatives of ammonia (NH3) where one or more hydrogen atoms are replaced by alkyl or aryl groups.

Explanation

• Morrison and Boyd Definition: Organic compounds derived from ammonia by replacement of one, two, or all three hydrogen atoms by alkyl or aryl groups.
• Solomons and Fryhle Definition: Characterized by a trivalent nitrogen atom bonded to one or more carbon atoms or hydrogen atoms, possessing a lone pair of electrons.
• Bonding & Geometry: Nitrogen has five valence electrons (three used for bonding, two as a lone pair). Hybridization is sp3, and geometry is pyramidal due to lone pair-bond pair repulsion.

Examples

• Methylamine (CH3NH2): Aliphatic amine used in pesticides and medicines.
• Aniline (C6H5NH2): Aromatic primary amine used to make dyes and polymers.

Real-Life Uses

• Pharmaceuticals: Drugs like adrenaline, ephedrine, and antihistamines contain amine groups for receptor binding.
• Vitamins: Essential for structures like Vitamin B1 (thiamine) and Vitamin B6 (pyridoxine).

Common Misconceptions and Corrections

Misconception: Amines are basic because they contain a hydroxyl group like NaOH.
Correction: Amines are basic because the lone pair of electrons on nitrogen can accept a proton (H+).

Definition

Classification is grouping amines based on how many hydrogen atoms of ammonia have been replaced by carbon chains or rings (Primary, Secondary, or Tertiary).

Explanation

• Primary (1°) Amines: One hydrogen replaced (R-NH2). Example: Ethylamine (CH3CH2NH2).
• Secondary (2°) Amines: Two hydrogens replaced (R2NH). Example: Dimethylamine ((CH3)2NH).
• Tertiary (3°) Amines: All three hydrogens replaced (R3N). Example: Trimethylamine ((CH3)3N).

Real-Life Uses

Quaternary ammonium salts act as cationic surfactants in fabric softeners and hair conditioners to neutralize static electricity.

Common Misconceptions and Corrections

Misconception: Tertiary amines have three carbon atoms in their main carbon chain.
Correction: Degrees refer to the number of carbon groups attached directly to the nitrogen atom.

Definition

Systematic naming of amines using IUPAC rules where primary aliphatic amines are named as alkanamines (alkane + amine with 'e' dropped).

Explanation

• IUPAC System: Drop 'e' from alkane and add '-amine' (e.g., Ethane becomes Ethanamine).
• Secondary/Tertiary Amines: Use 'N' as a locant to show substituent groups on nitrogen (e.g., N-methylethanamine).

Examples

• CH3CH2CH2NH2: Propan-1-amine (IUPAC) or Propylamine (Common).
• (CH3)2NCH2CH3: N,N-dimethylethanamine.

Common Misconceptions and Corrections

Misconception: Number the carbon chain from the end closest to the methyl group.
Correction: Number from the end giving the lowest locant number to the principal functional group (-NH2).

Definition

The 3-dimensional spatial arrangement of atoms in an amine molecule resulting from sp3 hybridization of nitrogen.

Explanation

• Nitrogen holds three single bonds and one lone pair, forming a pyramidal tripod shape.
• Bond angles (approx. 108°) are compressed below the tetrahedral angle of 109.5° due to strong lone pair-bond pair repulsion.

Real-Life Uses

The 3D pyramidal shape allows amine molecules to fit precisely into biological receptors like a key in a lock.

Common Misconceptions and Corrections

Misconception: Amines have a flat, planar structure like alkenes.
Correction: They are pyramidal, undergoing rapid nitrogen inversion (umbrella flipping), but static time-averaged geometry is pyramidal.

Definition

Chemical reactions used to synthesize amines from simpler starting materials via reduction or degradation.

Explanation

• Reduction of Nitro Compounds: Nitrobenzene reduced with Fe/HCl gives Aniline.
• Ammonolysis of Alkyl Halides: Yields a mixture of 1°, 2°, 3° amines and quaternary ammonium salts.
• Reduction of Nitriles: R-CN reduced with H2/Ni or LiAlH4 gives primary amines.
• Gabriel Phthalimide Synthesis: Yields pure primary aliphatic amines without side products.
• Hofmann Bromamide Degradation: RCONH2 + Br2 + 4NaOH → R-NH2 + Na2CO3 + 2NaBr + 2H2O.

Common Misconceptions and Corrections

Misconception: Ammonolysis of alkyl halides gives pure primary amine.
Correction: It creates a mixture because the primary amine formed reacts further with alkyl halides.

Definition

Physical characteristics such as boiling points, solubility, and odour governed by intermolecular hydrogen bonding and molecular mass.

Explanation

• Boiling Points: 1° and 2° amines form intermolecular hydrogen bonds (higher boiling points than non-polar compounds, lower than alcohols). Tertiary amines lack N-H bonds and boil lower.
• Solubility: Lower aliphatic amines dissolve in water via hydrogen bonding.
• Odour: Lower amines smell like rotting fish (e.g., putrescine and cadaverine).

Common Misconceptions and Corrections

Misconception: Tertiary amines have higher boiling points due to bulkiness.
Correction: They lack N-H bonds, so they cannot form hydrogen bonds with each other, resulting in lower boiling points.

Definition

Reactions of amines with other reagents driven by their basicity and nucleophilicity.

Explanation

• Basicity: Aliphatic amines are stronger bases than ammonia due to electron-donating alkyl groups (+I effect).
• Acylation: Primary and secondary amines react with acid chlorides/anhydrides to form amides.
• Carbylamine Test: Primary amines heated with chloroform and alcoholic KOH produce foul-smelling isocyanides.
• Reaction with Nitrous Acid: Aliphatic primary amines give unstable diazonium salts (yielding alcohols + N2); aromatic primary amines give stable diazonium salts at 0–5°C.

Common Misconceptions and Corrections

Misconception: Tertiary amines are always the strongest bases in aqueous solution.
Correction: Steric hindrance and solvation effects make secondary amines often stronger bases than tertiary amines in water.

Definition

Laboratory techniques like the Hinsberg Test (using benzene sulphonyl chloride) to distinguish between amine classes.

Explanation

• Primary Amine: Forms a sulphonamide soluble in aqueous KOH (has acidic hydrogen on N).
• Secondary Amine: Forms a sulphonamide insoluble in aqueous KOH (no acidic hydrogen).
• Tertiary Amine: Does not react at all (lacks N-H hydrogen).

Definition

The broad biological and industrial significance of amines in forming proteins, neurotransmitters, dyes, and drugs.

Explanation

Amines form amino acids, proteins, and neurotransmitters (dopamine, serotonin). In industry, they manufacture dyes, polymers, and medicines.

Definition

Diazotization: Reaction of primary aromatic amines with nitrous acid (NaNO2 + HCl) at 0 to 5°C to yield R-N2+ X-.

Explanation

Aniline + NaNO2 + HCl at 273–278 K yields Benzenediazonium chloride. If temperature exceeds 5°C, it decomposes into phenol and nitrogen gas.

Definition

Transformations of diazonium salts including Sandmeyer reactions (replacement by Cl, Br, CN using copper salts) and coupling reactions (azo dyes).

Explanation

The -N2+ group is an exceptional leaving group. Sandmeyer, Schiemann, and reduction reactions allow chemists to attach groups to benzene rings that cannot be introduced via direct substitution.

Definition

Organic derivatives of HCN containing -C≡N (Cyanides/Nitriles) and -N≡C (Isocyanides/Carbylamines) functional groups.

Explanation

• Cyanides: Ionic KCN provides carbon as a nucleophile, forming R-CN (linear sp hybridization).
• Isocyanides: Covalent AgCN attacks via nitrogen, forming R-NC (extremely foul odour).

Problem 1

An organic compound 'A' (C2H7N) on treatment with nitrous acid gives alcohol 'B' and evolves N2. 'A' reacts with Hinsberg's reagent to give a clear solution in aqueous KOH. Identify 'A' and 'B'.

Step-1: Formula C2H7N represents an aliphatic amine with 2 carbons.
Step-2: Reaction with HNO2 giving alcohol & N2 confirms 'A' is a primary aliphatic amine.
Step-3: Hinsberg product dissolving in KOH verifies 'A' is a primary amine.
Step-4: Compound 'A' is Ethanamine (CH3CH2NH2) and 'B' is Ethanol (CH3CH2OH).
        

Problem 2

Calculate the mass of Aniline required to prepare 9.3 grams of Benzenediazonium chloride (100% conversion). (Atomic masses: C=12, H=1, N=14, Cl=35.5).

Step-1: Equation: C6H5NH2 + NaNO2 + HCl → C6H5N2+Cl- + NaCl + 2H2O
Step-2: Molar mass of Aniline (C6H5NH2) = 93 g/mol.
Step-3: Molar mass of Benzenediazonium chloride = 140.5 g/mol.
Step-4: Mass of Aniline = (9.3 g × 93 g/mol) / 140.5 g/mol = 6.15 grams.
        

• General Amine: R-NH2, R2NH, R3N
• Hofmann Bromamide: RCONH2 + Br2 + 4NaOH → RNH2 + Na2CO3 + 2NaBr + 2H2O
• Carbylamine Reaction: RNH2 + CHCl3 + 3KOH → RNC + 3KCl + 3H2O
• Diazotization: C6H5NH2 + NaNO2 + HCl (0-5°C) → C6H5N2+Cl- + NaCl + 2H2O
• Sandmeyer Reaction: C6H5N2+Cl- + CuCl/HCl → C6H5Cl + N2

High-Performance Liquid Chromatography (HPLC) uses acetonitrile mobile phases to test purity of amine drugs. Automated peptide synthesizers build custom therapeutic proteins step by step using protected amino groups.

A pharmaceutical R&D team synthesizes a cardiovascular medication intermediate containing an aromatic primary amine and a nitrile group. Starting with nitrobenzene, they reduce it via Fe/HCl to aniline, perform diazotization at 0–5°C to form benzenediazonium chloride, apply the Sandmeyer reaction with CuCN to attach a nitrile group, and use Hinsberg tests to confirm intermediate purity before final acylation.

1. What is the hybridization of the nitrogen atom in aliphatic amines?
   Answer: C) sp3
   Explanation: Forms three single sigma bonds and holds one lone pair, resulting in sp3 hybridization and pyramidal geometry.
2. Which of the following reagents is used in the Hinsberg test?
   Answer: B) Benzene sulphonyl chloride
   Explanation: Reacts differently with primary, secondary, and tertiary amines.
3. The temperature maintained during diazotization of aromatic primary amines is:
   Answer: C) 0 to 5 degrees Celsius
   Explanation: Diazonium salts decompose rapidly at higher temperatures.
4. Which amine does not react with Hinsberg's reagent?
   Answer: C) Tertiary amine
   Explanation: Lacks a hydrogen atom attached to nitrogen, preventing sulphonamide formation.
5. Treatment of primary aliphatic amines with nitrous acid produces:
   Answer: B) Alcohols and nitrogen gas
   Explanation: Unstable aliphatic diazonium salts instantly decompose.
6. Which chemical test gives a foul-smelling isocyanide when heated with chloroform and alcoholic KOH?
   Answer: B) Carbylamine test
   Explanation: Specific for primary amines, producing offensive-smelling isocyanides.
7. In the reaction of alkyl halides with KCN, the major product formed is:
   Answer: B) Alkyl cyanide (nitrile)
   Explanation: KCN is ionic, releasing cyanide ions where carbon acts as the nucleophile.
8. Which of the following has the lowest boiling point among isomeric amines?
   Answer: C) Tertiary amine
   Explanation: Lacks N-H bonds, preventing intermolecular hydrogen bonding.
9. The conversion of an amide into a primary amine with one carbon less using Br2 and KOH is:
   Answer: B) Hofmann bromamide degradation
   Explanation: Uses bromine and strong base to degrade a primary amide.
10. Which reagent converts benzenediazonium chloride to fluorobenzene?
    Answer: C) HBF4 followed by heating
    Explanation: Known as the Schiemann reaction.

1. Q: Why are primary amines higher boiling than tertiary amines of comparable molecular mass?
   Answer: Primary amines possess N-H bonds allowing intermolecular hydrogen bonding, whereas tertiary amines lack N-H bonds entirely, requiring less energy to separate molecules.
2. Q: Write the chemical equation for the Gabriel Phthalimide synthesis of primary amines.
   Answer: Phthalimide + KOH → Potassium phthalimide; Potassium phthalimide + Alkyl halide → N-Alkylphthalimide; Hydrolysis with NaOH → Primary amine + Phthalic acid salt.
3. Q: Explain why aniline does not undergo Friedel-Crafts reaction.
   Answer: Aniline is a Lewis base and reacts with AlCl3 catalyst to form a salt, deactivating the aromatic ring and preventing alkylation or acylation.
4. Q: How can you distinguish between ethylamine and diethylamine using a chemical test?
   Answer: Using the Hinsberg test. Ethylamine forms a sulphonamide soluble in aqueous KOH, while diethylamine forms an insoluble oily layer.
5. Q: What is meant by diazotization? Give a standard equation.
   Answer: Conversion of a primary aromatic amine into a diazonium salt using nitrous acid at 0–5°C. Equation: C6H5NH2 + NaNO2 + 2HCl → C6H5N2+Cl- + NaCl + 2H2O.
6. Q: Why are aliphatic amines stronger bases than ammonia?
   Answer: Alkyl groups are electron-donating via the +I effect, increasing electron density on nitrogen and the availability of its lone pair.
7. Q: Write the reaction for Hofmann Bromamide degradation of ethanamide.
   Answer: CH3CONH2 + Br2 + 4NaOH → CH3NH2 + Na2CO3 + 2NaBr + 2H2O.
8. Q: Why is the diazonium group (-N2+) considered a versatile intermediate?
   Answer: It departs easily as stable nitrogen gas (N2), allowing replacement with halogens, cyanides, hydroxyl, or hydrogen that cannot be substituted directly.
9. Q: Give the reason why cyanides give carboxylic acids upon complete acid hydrolysis.
   Answer: Acidic hydrolysis successively converts the carbon-nitrogen triple bond through intermediate amides, removing nitrogen as ammonium ions and leaving a -COOH group.
10. Q: What happens when benzenediazonium chloride is treated with potassium iodide without heating?
    Answer: It forms iodobenzene directly along with N2 gas and KCl. Equation: C6H5N2+Cl- + KI → C6H5I + N2 + KCl.

• Amines are ammonia derivatives with sp3 hybridization and pyramidal geometry.
• Primary amines form soluble Hinsberg sulphonamides; secondary form insoluble layers; tertiary do not react.
• Diazotization requires strict temperature control (0–5°C) to prevent decomposition into phenol.
• KCN gives ionic cyanides (R-CN); AgCN gives covalent isocyanides (R-NC).

Mnemonic: Hinsberg Test Solubility Trick: "Primary is Pleasing (Dissolves), Secondary is Stubborn (Insoluble), Tertiary Takes a nap (No reaction)."