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Flashcards in Haloalkanes Deck (53)
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1

What mechanism is used to form haloalkanes

Free radical substitution

2

Conditions for radical substitution

UV light

3

What does free radical substitution produce

A haloalkane and a hydrogen halide

4

What are the 4 stages of free radical substitution?

Initiation
1st propagation
2nd propagation
Termination

5

What is a free radical?

A very reactive species with an impaired molecule

6

Describe initiation

X-X bonds are weaker than C-H bonds so are broken first
UV light causes covalent bond to break between halogen molecules, creating 2 halogen radicals

X2 —> 2X•

7

Equation for CH4 in first propagation stage of free radical substitution

CH4+X• —> •CH3 + HX

8

Equation for CH4 in second propagation stage of free radical substitution

•CH3 + X2 —> CH3X + X•

9

There is a chain of first and second propagations. When does this chain end?

Once you run out of halogen molecules or alkanes

10

What is termination?

The remaining unstable species combining to make neutral molecules

11

What are the 3 possible termination steps?

X•+X• —> X2

•CH3 + X• —> CH3X

•CH3 + •CH3 —> CH3CH3

12

What is the alkyl radical from CH4?

•CH3

13

What happens if an excess of the halogen is added to a free radical substitution?

Further substitution is possible, leading to the formation of CH2X2, CHX3, or CCl4

14

How can you reduce the chance of further substitution?

Using an excess of the alkanes

15

What do curly arrows represent?

The movement of an electron pair

16

Where must curly arrows always start?

At a bond or a lone electron pair

17

Define nucleophile

A species that donates a lone pair of electrons

18

Define Electrophile

Accepts a lone pair of electrons

19

What a carbon - halogen bonds?

Polar

The halogen has a greater electronegativity so is delta negative
The C is delta positive

20

Why is the C readily attacked by a nucleophile?

The C is delta positive

21

Describe the 3 steps of nucleophilic substitution

Lone pair of nucleophile forms a Covalent bond with delta positive C atom

Electrons on C-halogen bond move onto halogen atom, breaking the C-X bond, and forms a halide ion

22

Order C- halogen bonds from strongest to weakest

Comment on the reactivity

C-F
C-Cl
C- Br
C- I

Reactivity increases as you go down the group

23

Give reagents and conditions for nucleophilic addition to form alcohols

Reagents: NaOH
Conditions: warm, aqueous

24

Are haloalkanes polar?

Yes

25

Give reagents and conditions for nucleophilic addition to form nitriles

How does this affect the C chain

KCN
Aqueous ethanol

(CN- adds an extra carbon to the chain)

26

Name CH3CH(CN)CH3

2-methyl propane nitrile

27

Give reagents and conditions for nucleophilic addition to form primary amines

Excess NH3

28

Why is excess NH3 used to form primary amines

To avoid further substitution

29

How can RNH2 act as a nucleophile?

There is a lone pair on N

30

How to get a high yield of quaternary ammonium salt

Use a large excess of haloalkane