Halogenoalkanes

Question 1

Preparation

Answer 1

1. From alkenes through E.A.
   C&R :
   - X2 in CCl4 r.t.
   -dry HX(g) r.t.
   -X2(aq) r.t.
2. From alkanes
   FRS
   C&R:
   limited X2(g), UV light
3. From alcohols through Nu:sub
   C&R :
4. PCl3 anhydrous, heat
5. PCl5 anhydrous, r.t.
   3.SOCl2 anhydrous, r.t.
   4.dry HX, r.t.

Question 2

Elimination

Answer 2

to form alkenes
- ethanolic KOH, heat

Question 3

Physical properties

Answer 3

1. Non polar
2. dissolves in non polar solvents
3. MP/BP depends on degree of branching, size of electron cloud

Question 4

Nucleophilic substitution reactions

Answer 4

1. Form alcohol
   - NaOH, heat
2. Form nitriles
   - ethanolic KCN, heat
   3.Form primary amines
   - excess NH3 in ethanol and heat in a sealed tube
3. Form quaternary amines
   -limited NH3 in ethanol

Question 5

Nitriles reaction

Answer 5

1. Acidic hydrolysis to form carboxylic acid
   - HCl, heat
2. Alkaline hydrolysis to form carboxylate salt
   - NaOH, heat
3. Reduction to form -CH2NH2
   - LiAlH4 in dry ether/ H2 /Ni catalyst and heat

Question 6

Why halogenoarenes and alkenyl halides are resistant to nu:sub

Answer 6

1. delocalisation of lone pair of electrons on halogen into electron rich region
2. due to p-p orbital overlap
3. strengthening C-X bond

Question 7

Nu:sub mechanisms

Answer 7

1. Sn1
   - 1 reacting particle in the slow step to generate a carbocation
   In the fast step carbocation reacts w nucleophile
   - secondary and tertiary alkyl halides undergo this mech. as they can form stable carbocations
2. Sn2
   - 2 reacting particles in slow step
   - primary/secondary alkyl halides
   - show stereochemistry
   -product formed has inverted stereochemistry

For both, draw curly arrows and nucleophile approaching from the back