Hydrocarbons

Question 1

Why are alkanes called ‘paraffins’?

Answer 1

Because they have very little affinity (less reactivity)

Question 2

How to prepare alkanes? List various methods.

Answer 2

1. From Unsaturated Hydrocarbons
2. From Carboxylic Acids
3. From Alkyl Halides

Question 3

Alkene —-> Alkane

Answer 3

Name of the method: Catalytic Hydrogenation
Substrate: Alkene
Reagent: Dihydrogen Gas
Catalysts: Pd/Ni/Pt

Question 4

Alkyl Halides —-> Alkane

Answer 4

Method 1
Reagent: Zinc and dil HCl

Method 2 (WURTZ REACTION)
Reagent: Na/ Dry Ether
Substrate: 2 moles of alkyl halides
Product: Alkane with even number of carbons (symmetrical alkanes)

Question 5

WURTZ REACTION

Question 6

COREY HOUSE ALKANE SYNTHESIS

Question 7

KOLBE’S ELECTROLYSIS

Question 8

DECARBOXYLATION

Question 9

HALOGENATION OF ALKANES

Answer 9

– Temperature: 573-773K
– In presence of UV light or diffused sunlight
– radical mechanism

Question 10

Why is Halogenation not carried out using F or I?

Answer 10

– F is too violent and the reaction cannot be controlled
– Iodination is very slow and is a reversible process. The HI produced is a reducing agent and reduces the alkyl halide back to alkane. Thus, we use a reducing agent iodic acid (HIO3) /Nitric Acid.

Question 11

3 steps of halogenation

Answer 11

1. initiation
2. chain propogation
3. termination