AMINES ANSWER SCHEMES

ANSWER
SCHEME

AMINES

No Answer

1. (a) N,N-dimethylmethanamine < N-methylethanamine < 1-propanamine

● N,N-dimethylmethanamine has the lowest boiling point because
it is tertiary amine, so it cannot form hydrogen bonds between
molecules.

● 1-propanamine (1o amine) has higher boiling point than N-
methylethanamine (2o amine) because 1-propanamine can form
more hydrogen bonds between molecules than N-
methylethanamine

(b)

CH3CH2CH2CH3 < (CH3)2CHNH2 < CH3CH2CH2NH2 <
CH3CH2CH2OH

● Alkane is not capable of forming hydrogen bonding between the
molecules, is only has weak van der Waals forces. Hence, the
boiling point of CH3CH2CH2CH3 is the lowest among all.

● The electronegativity of O is higher than N. Hence, the hydrogen
bonding of alcohol molecules is stronger than the amines.
Therefore, CH3CH2CH2OH has the highest boiling point.

● Straight chain molecule has bigger surface area and accounts
for stronger van der Waals forces and higher boiling point.
Hence, CH3CH2CH2NH2 has higher boiling point than
(CH3)2CHNH

(c)

pentane < N,N-dimethylethanamine < 1-butanamine < 1-butanol

● The electronegativity of O is higher than N. Hence, the hydrogen
bonding of alcohol molecules is stronger than the amines.
Therefore, 1-butanol has the highest boiling point.

● The boiling point of primary amine is stronger than tertiary amine
because primary amine can form hydrogen bond between
molecules while tertiary amine cannot. Therefore, 1-butanamine
has higher boiling point than N,N- dimethylethanamine.

● Both pentane and N,N-dimethylethanamine cannot form
hydrogen bond but pentane is nonpolar while N,N-
dimethylethanamine is polar. The dipole-dipole forces in N,N-
dimethylethanamine is stronger than the London forces in
pentane. Hence, pentane has the lowest boiling point

No Answer

2. (a) All the four amines are soluble in water. 1-propanamine is the most
soluble as it can form more intermolecular hydrogen bonds with
water molecules. N,N-dimethylmethanamine is the least soluble as it
can form less number of intermolecular hydrogen bonds with water
molecules.

(b)

CH3COOH > CH3CH2NH2 > CH3CH2CH2NH2

• CH3COOH is most soluble in water because it can form more
hydrogen bonding with water molecules compared to alcohol and
amine

• CH3CH2NH2 is more soluble than CH3CH2CH2NH2 because it has
smaller hydrophobic area (both can form the same number of
hydrogen bond).

3.

Ammonia < N,N-dimethylethanamine < ethanamine < N-
methylethanamine

• N-methylethanamine is more basic than ethanamine because it has
2 alkyl groups while ethanamine only has 1 alkyl group. Alkyl group
is an electron donating group which makes the lone pair on N atom
more readily to accept proton.

• Although N,N-dimethylmethanamine has more alkyl groups, the
presence of 3 alkyl groups sterically decrease the availability of
lone pair on N to accept proton. Thus, N,N-dimethylmethanamine
is less basic than N-methylethanamine.

• Ammonia is less basic because it has no alkyl group.

4.
A = CH3CH2NH2

B = (CH3)3CCH2CH2NH2

C = LiAlH4/H +

–

O N+ O O
N+ –
O

D=
E = Br2, NaOH

No Answer

5. B = NH2+ C = Br2, NaOH

A= Cl

D= G=

OH
N

H

E = CH3Cl F = LiAlH4/ H+ H = NH3