Questions - Answers
2 Marks Questions
1. What is "Sand meyer's reaction"?
A: The reaction in which diazonium group of diazonium salt is replaced by the nucleophiles like Cl- or Br- or CN- in presence of Cu+ ion & corresponding halogen acid.
e.g.:
2. What is "Carbylamine reaction"?
A: A dirty smelling compound carbyl amine (Isocyanide) is formed when aliphatic or aromatic primary amine is heated with chloroform and ethanolic KOH.
e.g.:
3. What is "Gatterman reaction"?
A: The reaction in which diazonium group of diazonium salt is replaced by the nucleophiles like Cl- or Br- or CN- in presence of corresponding halogen acid and Cu powder.
e.g.:
4. What is "Hoffman bromamide degradation reaction"?
A: The reaction in which primary amine is prepared by treating alkyl or aryl amide with Br2 in aqueous or ethanolic NaOH solution.
e.g.:
5. Give the structures of A, B and C in the following reaction.
A:
6. Gabriel Phthalimide synthesis exclusively forms primary amines only. Explain why?
A: As only one H atom is bonded to the N of phthalimide, only one alkyl group can be placed on N. So this synthesis is used only for the preparation of aliphatic primary amines.
7. Why cannot aromatic primary amines be prepared by Gabriel Phthalimide synthesis?
A: As aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide, aromatic primary amines can not be prepared by Gabriel Phthalimide Synthesis. So, only aliphatic primary amines can be prepared.
8. PKb of aniline is more than that of methyl amine. Explain Why?
A:
In aniline electron pair present on N is involved in conjugation (resonance) and is less available for protonation than that of methyl amine. So aniline is less basic i.e. lowest Kb or highest PKb. Therefore PKb of aniline is more than that of methylamine.
9. How would you prepare the following?
a) N, N - Dimethylpropanamine from ammonia.
b) Propanamine from Chloroethane.
A:
10. Explain why amines are less acidic than alcohols of comparable molecular masses?
A: The compound that can easily release (donate) H+ is more acidic. As N - H bond in amines is less polar (H+ is not released easily) than O - H bond in alcohols (due to electronegativity of O > N). So amines are less acidic than alcohols of comparable molecular masses.
11. How do you prepare Ethyl Cyanide and Ethyl isocyanide from a common alkylhalide?
12. Compare the basicity of the following in gaseous and aqueous state and arrange them in increasing order of basicity. CH3NH2, (CH3)2NH, (CH3)3 N and NH3.
A: Due to +I effect, alkyl group has electron releasing tendency. So in gaseous state the basicity of amines is NH3< CH3 NH2< (CH3)2 NH < (CH3)3N
Where as in aqueous state basicity of amines not only depends upon +I effect but also depends upon solvation effect and steric hindrance. So the basicity of amines in aqueous state is NH3< (CH3)3N < CH3 NH2< (CH3)2NH
4 Marks Questions
1. Complete the following conversions. Aniline to a) Fluorobenzene b) Cyanobenzene c) Benzene and d) Phenol
A:
2. Write the steps involved in the coupling of benzene diazonium chloride with aniline and Phenol
A: -N2Cl group is paradirecting. The reaction in which diazonium salt reacts with aromatic amine or phenol, azo compound having the general formula Ar - N = N - Ar is called coupling (example of electrophilic substitution)
3. Complete the following conversions.
