Nitrogen cmpds

Question 1

Amines
Preparation

Answer 1

1. Reduction of nitriles to RCH2NH2
   LiAlH4 in dry ether/ Ni/H2 and heat
2. Reduction of amide to RCH2NH2
   LiAlH4 in dry ether/ H/Ni heat
3. Acid base
   Nitrobenzene to phenylamine
   Sn catalyst, HCl (aq) and heat, followed by NaOH(aq)
   NaOH is added to deprotonate NH3+ attached to benzene to form phenylamine
4. Nu:sub of halogenoalkane
   Excess NH3 in ethanol in sealed tube heat

Question 2

Chemical properties of amine

Answer 2

Basic
NH2 is an H+ acceptor due to availability of lone pair on N

Question 3

Factors affecting degree of basicity

Answer 3

1. Delocalisation/ electron withdrawing groups
   - The delocalisation of electrons from N into benzene ring/ electron rich region makes lone pair less available to accept H+ hence basicity is lower
2. Presence of electron donating groups
   - The presence of electron donating groups makes the lone pair more available to donate l.p to H+ hence basicity increases
3. S character
   - As S character increase (depending on hybridsation state of N) basicity decreases as lone pair is more strongly attracted to the nucleus in the hybrid orbital

Question 4

Reaction of amines

Answer 4

1. Condensation to form amide
   - RCOCl
   - Amine
2. Acid base to form CA salt
   - HCl (aq)
   - NH3+Cl as product
3. Nu:sub
   - Limited RX NH3 in ethanol heat in sealed tube
   - Can form primary, secondary, tertiary and quaternary
4. Electrophilic sub
   - Trisub product 2,4,6 bromo- phenylamine
   - white ppt, orange Br2 decolourises

Question 5

Amides
Preparation

Answer 5

Condensation
RCOCl
Amine (primary, sec, tertiary)

Question 6

Chemical property

Answer 6

Neutral because NH2 is in close proximity to electron withdrawing C=O. The highly electronegative O atom in C=O withdraws electrons from C=O bond. Lone pair on N significantly delocalises into adjacent C=O resulting in lone pair on N not being available to accept H+.

Question 7

Reaction:
amides

Answer 7

1. Acidic hydrolysis
   HCl(aq), heat
2. Alkaline hydrolysis
   NaOH(aq), heat
3. Reduction to form R-CH2NH2
   LiAlH4 in dry ether/ H/Ni heat

Question 8

Amino acid
Chemical properties

Answer 8

1. Exists as a zwitterion which is electrically neutral
   - Oppositely charged COO- , NH3+ depending on pH
2. Amphoteric
   Acts as a buffer by regulating pH by reacting with small amounts of H+ or OH- by either protonating or deprotonating

Question 9

Physical properties

Answer 9

Has a giant crystal ionic lattice struc with strong ionic bonds between opp. Charged groups hence high MP/BP

Question 10

Reaction:
amino acids

Answer 10

1. Peptide formation (condensation) to form protein
2. Hydrolysis of protein
   HCl (aq) , heat

Question 11

NH2 and COOH attached to alpha C are less acidic than side chain NH2 or COOH why?

Answer 11

NH2
When in close proximity to a-C, NH2 is in close proximity to electron withdrawing COOH group hence lone pair on N is less available to accept H+ making it less basic. Side chain NH2 protonates in preference to alpha NH2 as it is more basic in an acidic env.

COOH
R group- COOH is attached to electron donating R group which intensifies negative charge on COOH.Therefore destabilising the side chain COOH group. Hence it is less acidic than a-COOH group which is in close proximity to an electron withdrawing NH3+ group which disperses the negative charge on COOH stabilising the a-COOH. Hence a-COOH is more acidic and dissociates in preference to R group-COOH. (deprotonates in preference since its more acidic in basic env)

Question 12

• pH > pKa deprotonation