Nitrogen chemistry

Question 1

difference between aliphatic and aromatic amine

Answer 1

If the R group is an alkyl group (methyl, ethyl, etc) then then it is an aliphatic amine; if it is an aryl group (benzene ring or phenyl) then it is an aromatic amine

Question 2

how are amides formed

Answer 2

from the condensation reaction of carboxylic acids or acyl chlorides with ammonia or amines

Question 3

why are amino acids said to be amphoteric

Answer 3

A basic amino (-NH2) group
An acidic carboxylic acid (-COOH) group
Due to the presence of both a basic and acidic group in amino acids,

Question 4

what do amines react with strong acids to form

Answer 4

ammonium salts

Question 5

what do you add to ammonium salt to convert it back into amine

Answer 5

Addition of NaOH to an ammonium salt will convert it back to the amine

Question 6

how to form amine via nucleophilic substitution

Answer 6

reaction between a halogenoalkane with ammonia in a sealed tube.

One mole of halogenoalkane reacts with two moles of ammonia, producing a primary amine and an ammonium salt

Question 7

how can amines be formed from the reduction of nitriles

Answer 7

LiAlH4 dry ether or H2 and Ni catalyst

Question 8

how does amine react with water

Answer 8

amine acts as a base to form an alkaline solution
Lone pair on nitrogen accepts a hydrogen from water molecules releasing OH-

Question 9

how does amine react with acids

Answer 9

amine acts as a base and accepts a proton to form a quaternary ammonium salt

Question 10

why are aliphatic amines stronger bases than aromatic amines

Answer 10

benzene ring draw electron density away from the nitrogen making the lone pair less available for dative bonding with ammonia so decreasing amine basicity

alkyl groups push electron density towards the nitrogen atom making the lone pair more available and increase amine basicity

Question 11

how can aromatic amines be produced

Answer 11

reduction of nitrobenzene using concentrated HCL and tin catalyst

Question 12

what is condensation polymerisation

Answer 12

polymer is produced by repeated condensation reactions between monomers

Question 13

how can condensation polymers be identified

Answer 13

monomers are linked by ester or amide bonds

Condensation polymers can be formed by:
dicarboxylic acids and diols
dicarboxylic acids and diamines
amino acids

Question 14

what is an amide link

Answer 14

key functional group in a polyamide

-CONH

Question 15

what is a zwitterion and how is it formed

Answer 15

an ion with both a positive (-NH3+) and a negative (-COO-) charge

An amino acid molecule can interact within itself to form a zwitterion

Question 16

what does a solution of amino acids in water exist as

Answer 16

zwitterions with both acidic and basic properties

They act as buffer solutions as they resist any changes in pH when small amounts of acids or alkali are added

Question 17

what happens when acid is added to zwitter ion

what happens when base is added to zwitter ion

Answer 17

The -COO- part of the zwitterion will accept an H+ ion to reform the -COOH group

The -NH3+ part of the zwitterion will donate an H+ ion to reform the -NH2 group
This causes the zwitterion to become a negatively charged ion

Question 18

what is isoelectric point of an amino acid

Answer 18

pH can be slightly adjusted to reach a point at which neither the negatively charged or positively charged ions dominate and the amino acid exists as a neutral zwitterion

Question 19

what does amino acid and alkali react to form such as sodium hydroxide

Answer 19

salt and water

H2NCHRCOOH + NaOH ⇌ H2NCHRCOO- Na+ + H2O

Question 20

what does it mean that all amino acids but glycine are chiral

Answer 20

they are optically active so a solution of amino acids will rotate plane polarised light.

Question 21

how can polypeptide chains in a protein by broken down into amino acids

Answer 21

The polypeptide chains in a protein can be broken down into their individual amino acids by prolonged heating with concentrated hydrochloric acid.
This breaks the peptide bonds between amino acids

Question 22

how can the amino acids produced by hydrolysis be identified

Answer 22

simple chromatography

Using a suitable solvent, the individual amino acids will rise to different heights on the chromatography paper

As the amino acids are colourless, the chromatogram is sprayed with a developing agent so that the amino acid positions can be seen

Once the positions of the amino acids have been established, their Rf values can be calculated

Question 23

why is dibutylamine more alkaline than butylamine

Answer 23

Butyl / alkyl groups are electron donating / are electron pushing / are electron releasing
Two (alkyl) groups in dibutylamine (but only one in butylamine)
Lone pair (of electrons) on the nitrogen more readily available / higher electron density on the nitrogen or NH2 or amine group / N more delta negative / N or NH, accepts a proton more readily

Question 24

why penylamine is much less alkaline than butylamine solution

Answer 24

For the idea of the lone pair being withdrawn
towards the ring
Lone pair pulled into the ring

For the idea of the lone pair being less
available

Question 25

how can you use chromatography with samples of amino acids to show which amino acid the protein contained

Answer 25

Spot (of hydrolysate) on paper/tlc/thin layer chromatogram
Spi aci
(1)
(1)
KP2 Marker spots of known amino-acids/measure Rf
КР3 Run in (suitable)
solvent/discussion of comparative solubilities in phases
(1)
KP4 (Spray with) ninhydrin (and heat) [Stand alone mark]
(1)
KP 5 Marker spots and the unknown spots correspond
ALLOW
Compare R values of marker spots with hydrolysate spots