Ch36_-_Nitrogen_compounds

36.1 Introduction (SB p.68)
Examples of 3° amines:
Addition of the fourth organic group to tertiary amine yields a quaternary ammonium ion
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New Way Chemistry for Hong Kong A-Level Book 3B
New Way Chemistry for Hong Kong A-Level Book 3B
36.1 Introduction (SB p.67)
Organic nitrogen compounds: • amines, amino acids, amides and nitro compounds • According to the number of organic groups (both alkyl or aryl groups) directly bonded to the nitrogen atom, amines are classified as:
36.3 Physical Properties of Amines (SB p.70)
• •
Lower members of amines are gases and have a characteristic ‘ammonia’ odour. The higher members are liquids with a distinctive ‘fishy’ odour
Formula
Boiling Melting Density at point (°C) point (°C) 20°C (g cm–3) ° ° ° 7.4 56.3 196 302 3.5 89.4 194 365 –96 –48 –57 52.8 –117 –115 2.5 126 — 0.707 0.989 — — 0.728 0.956 —
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36.3 Physical Properties of Amines (SB p.71)
• 3° amines have lower b.p. and m.p. than 1° and 2° ° ° ° ∵ all hydrogen in 3° amines are replaced by organic groups ⇒ no hydrogen bond can be formed
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36.3 Physical Properties of Amines (SB p.71)
Density Molecular mass of amines ↑ ⇒ densities ↑
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(CH3)2NH2 (CH3CH2)2NH2 C6H5NHCH3 (C6H5)2NH (CH3)3NH2 (CH3CH2)3NH2 C6H5N(CH3)2 (C6H5)3N
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New Way Chemistry for Hong Kong A-Level Book 3B
36.3 Physical Properties of Amines (SB p.71)
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New Way Chemistry for Hong Kong A-Level Book 3B
36.2 Nomenclature of Amines (SB p.70)
Check Point 36-2 36Complete the following table by filling in the structural formulae or IUPAC names of the amines.
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New Way Chemistry for Hong Kong A-Level Book 3B
36.1 Introduction (SB p.67)
Check Point 36-1 36Classify the following amines as primary, secondary or tertiary amines.
Boiling Point and Melting Point 1° or 2° amines can form strong hydrogen bonds with each other
⇒ the b.p. is higher than those of alkanes but lower than those of alcohols of comparable molecular masses ∵ O – H bond is more polar than N – H bond as oxygen is more electronegative ⇒ stronger hydrogen bonds are formed between alcohol molecules
Primary amines: Methylamine Ethylamine Propylamine Butylamine Pentylamine Hexylamine Phenylmethylamine Phenylamine
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CH3NH2 CH3CH2NH2 CH3(CH2)2NH2 CH3(CH2)3NH2 CH3(CH2)4NH2 CH3(CH2)5NH2 C6H5CH2NH2 C6H5NH2
IUPAC name (a) Structural formula (a) 1-Methylpropylamine (b) (b) 2-Aminophenol (c) (c) Diethylamine
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
36.3 Physical Properties of Amines (SB p.72)
Solubility • The solubility of amines in water: 1° amines > 2° amines > 3° amines ° ° °
∵ The intermolecular hydrogen bonds formed between 2° or 3° amines and water molecules decrease • Amines are soluble in common organic solvents, e.g. hexane, ethanol and propanone
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New Way Chemistry for Hong Kong A-Level Book 3B
36.1 Introduction (SB p.67)
Examples of 1° amines:
Examples of 2° amines:
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New Way Chemistry for Hong Kong A-Level Book 3B
36.3 Physical Properties of Amines (SB p.72)
Solution: Match the boiling points 65°C, –6°C and –88°C with the ° ° ° Compounds CH3CH3, CH3NH2 °and CH3OH. Explain your Boiling Point (°C) compounds CH3CH3 briefly. –88 answer Answer CH3NH2 –6
New Way Chemistry for Hong Kong A-Level Book 3B
36.3 Physical Properties of Amines (SB p.70)
Amine Secondary amines: Dimethylamine Diethylamine N-Methylphenylamine Diphenylamine Tertiary amines: Trimethylamine Triethylamine N,N-Dimethylphenylamine Triphenylamine
36.1 Introduction (SB p.68)
Aromatic amines are formed when one or more hydrogen atoms in the ammonia are replaced by phenyl or substituted phenyl groups e.g.
Chapter 36
Nitrogen CompБайду номын сангаасunds
36.1 36.2 36.3 36.4 36.5 36.6 36.7
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Introduction Nomenclature of Amines Physical Properties of Amines Preparation of Amines Reactions of Amines Uses of Amines and their Derivatives Amino Acids
CH3OH 65 Ethane (CH3CH3) is a non-polar compound. In pure liquid form, ethane molecules are held together by weak van der Waals’ forces. However, both methylamine (CH3NH2) and methanol (CH3OH) are polar substances. In pure liquid form, their molecules are held together by intermolecular hydrogen bonds. As van der Waals’ forces are much weaker than hydrogen bonds, ethane has the lowest boiling point among the three. Besides, as the O – H bond in alcohols is more polar than the N – H bond in amines, the hydrogen bonds formed between methylamine molecules are weaker than those formed between methanol molecules. Thus methylamine has a lower boiling point than 16 New Way Chemistry for Hong Kong A-Level Book 3B methanol.
Amine Formula Boiling Melting Density at point (°C) point (°C) 20°C (g cm–3) ° ° ° –6.3 16.6 48.6 77.8 103 130 185 184 –92.5 –84 –83 –50.5 –55 –19 10 –6.2 — — 0.719 0.741 0.761 0.768 0.981 1.022
1° amines are named as alkylamines e.g.
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36.2 Nomenclature of Amines (SB p.69)
• 2° and 3° amines are named in the same general way • If the organic groups attached to the nitrogen are the same, use the prefixes ‘di-’ or ‘tri’ • If they are not the same, use the prefixes ‘N-’ or ‘N,N-’ to designate the substituents e.g.
I is a primary amine. II is a tertiary amine. III is a secondary amine.
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
36.2 Nomenclature of Amines (SB p.69)