20 Nitrogen Compounds

Question 1

Primary, Secondary, Tertiary Amines

Answer 1

Number of R groups attached to the N atom
Primary: 1 R group
Secondary: 2 R groups
Tertiary: 3 R groups
Quaternary ion: 4 R groups, +1 charge

Question 2

Factors affecting boiling point of amines

Answer 2

1. Increasing C chain -> increasing id-id interactions
2. primary/secondary > tertiary (due to hydrogen bonding)

Question 3

Factors affecting solubility of amines

Answer 3

1. Lone pair on N atom -> hydrogen bonds with H2O molecules
2. Longer carbon chain hinders formation of hydrogen bonding

Question 4

Factors affecting amines as a base

Answer 4

1. Lone pair of N atom readily accepts proton by forming dative bond
2. Electron-donating substituents increase basicity
3. Electron-withdrawing substituents decrease basicity
4. Phenylamine weaker base than NH3 due to delocalisation of lone pair into the ring

Question 5

Nitrile -> Amine

Answer 5

Reduction
LiAlH4 in dry ether
H2(g), Ni, heat

Question 6

Amide -> Amine

Answer 6

Reduction
LiAlH4 in dry ether

Question 7

Nitrobenzene -> Phenylamine

Answer 7

Reduction
1. Sn, conc HCl, heat
2. NaOH (aq)

Question 8

Alkyl Halides -> Amines

Answer 8

Nucleophilic substitution
excess ethanolic NH3, heat

Question 9

Amine -> Amide

Answer 9

Condensation with Acyl Chloride
HCl produced as byproduct

Question 10

Factors affecting boiling point of Amides

Answer 10

Formation of dimers in liquid phase, due to intermolecular hydrogen bonding

Question 11

Why are amides neutral and not basic?

Answer 11

p-orbital of N atom overlaps with π electron cloud of carbonyl group (C=O) -> delocalisation of lone pair

Question 12

Amide -> Carboxylic Acids

Answer 12

Hydrolysis
dilute HCl/H2SO4, HUR
dilute NaOH, HUR (alkaline medium)

Question 13

Amino Acids

Answer 13

Contains at least 1 -NH2 and 1 -COOH group

Question 14

Zwitterion formation of Amino Acids

Answer 14

Intramolecular acid-base reaction
Proton from -COOH transferred to -NH2, resulting in -COO- and -NH3+

Question 15

Properties of Amino Acids

Answer 15

1. Enantiomerism
2. High melting point due to strong electrostatic forces of attraction between oppositely charged groups of zwitterions
3. Soluble in H2O due to ion-dipole interactions

Question 16

Chemical properties of Amino Acids

Answer 16

1. Amphoteric
2. pH>pKa of group -> protonated form
3. pH<pKa of group -> deprotonated form
4. Buffering action

Question 17

Peptide bond

Answer 17

-NHCHCO-
N-terminus (-NH2) on the left, C-terminus (-COOH)