Organics - halogenation

Question 1

Bond cleavage

Answer 1

splitting of a chemical bond

Question 2

BDE

Answer 2

Bond dissociation energy
(energy required to break 1 mol of bonds)

Question 3

Describle the type of bond cleavage X2 occurs in free radical sub.

Answer 3

Homolytic

Question 4

Describle the bond cleavage of X2 using MO theory

Answer 4

1. initially there’s a bond order of 1 (fully filled MO)
2. prescence of UV/heat
3. promotes one electron to anti-bonding orbital
4. no net stability
5. radicals fly apart

Question 5

e.g. butane

which mono-sub. product should be major + WHY
(by statistic)

in free radical subsitution with Cl2

Answer 5

1-chloro ( as there are 6/10 electron in 1,4 position)

Question 6

e.g. butane

which mono-sub. product should be major + WHY
(from experiements)

in free radical subsitution with Cl2

Answer 6

2-chloro ( lower activation energy )

Question 7

Trends of carbocation with class of carbon

Answer 7

1. ↑class
2. more alkyl groups
3. less +ve
4. ↑ stable carbocation

↑likely to form

Question 8

explaination of carbocation stability

Describle the inductive effect

Answer 8

1. alkyl group is more electron-releasing
2. electron density is pulled towards centre
3. making it less +ve

Question 9

explaination of carbocation stability

Describle hyperconjugation

Answer 9

1. sp2 hybridised carboncation
2. has a vacant 2p orbital
3. sp3 alkly group donates electron
4. bond order goes from 0 -> 0.5

Question 10

Describle the hammond postulate rule

Answer 10

1. exo - resembles reactants
2. endo - resembles products

refer to the free-energy diagram for greater logic reasoning

Question 11

For alkane halogenation

What happens if the first step of propagation is endo

Answer 11

1. closer to product
2. i.e. the carbon radical
3. stability of the carbon radical will have ↑ effect the rate