Halogenoalkanes Flashcards
1
Q
Preparation
A
- From alkenes through E.A.
C&R :
- X2 in CCl4 r.t.
-dry HX(g) r.t.
-X2(aq) r.t. - From alkanes
FRS
C&R:
limited X2(g), UV light - From alcohols through Nu:sub
C&R : - PCl3 anhydrous, heat
- PCl5 anhydrous, r.t.
3.SOCl2 anhydrous, r.t.
4.dry HX, r.t.
2
Q
Elimination
A
to form alkenes
- ethanolic KOH, heat
3
Q
Physical properties
A
- Non polar
- dissolves in non polar solvents
- MP/BP depends on degree of branching, size of electron cloud
4
Q
Nucleophilic substitution reactions
A
- Form alcohol
- NaOH, heat - Form nitriles
- ethanolic KCN, heat
3.Form primary amines
- excess NH3 in ethanol and heat in a sealed tube - Form quaternary amines
-limited NH3 in ethanol
5
Q
Nitriles reaction
A
- Acidic hydrolysis to form carboxylic acid
- HCl, heat - Alkaline hydrolysis to form carboxylate salt
- NaOH, heat - Reduction to form -CH2NH2
- LiAlH4 in dry ether/ H2 /Ni catalyst and heat
6
Q
Why halogenoarenes and alkenyl halides are resistant to nu:sub
A
- delocalisation of lone pair of electrons on halogen into electron rich region
- due to p-p orbital overlap
- strengthening C-X bond
7
Q
Nu:sub mechanisms
A
- 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 - 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