Synthesis 2a - Haloalkanes

Question 1

What are haloalkanes?

Answer 1

Substituted alkanes in which one or more of the hydrogen atoms is replaced with a halogen atom

Question 2

How are haloalkanes prepared?

Answer 2

From the Electrophilic addition of halogens or hydrogen halides to alkenes

Question 3

How are haloalkanes classified?

Answer 3

According to the number of alkyl groups attached to the carbon atom containing the halogen atom.

Question 4

How do haloalkanes form alkenes

Answer 4

Take part in elimination reactions to form alkenes using a strong base, such as potassium or sodium hydroxide in ethanol.

Question 5

How do haloalkanes form alcohols?

Answer 5

When refluxed with aqueous alkalis monohaloalkanes undergo nucleophilic substitution forming alcohols.

Question 6

How do haloalkanes form ethers?

Answer 6

Nucleophilic substitution with alcoholic alkoxides to form ethers.

Question 7

How do haloalkanes form carboxylic acids? (2 steps)

Answer 7

Nucleophilic substitution reaction with ethanol’s cyanide to form nitriles that can be hydrolysed to carboxylic acids.

Question 8

Sn1

Answer 8

1 species in rate determining step and occurs in minimum of 2 steps via a trigonal planar carbocation intermediate.

Question 9

Sn2

Answer 9

2 species in rate determining step and occurs in a single step via a single 5 centered, trigonal bipyramidal transition state.

Question 10

Inductive affect explanation?

Answer 10

Alkyl groups tend to release binding electrons towards attached atom to alter bond polarity.
The larger the alkyl group the greater the inductive effect, this release of negative charge towards the central C atom will stabilise the +vely charged C which is produced as an intermediate in the SN1 mechanism.
The greater the number of alkyl groups attached to the +vely charged C and the larger the size of the alkyl groups, the more likely the reaction will proceed via an Sn1 mechanism.

Question 11

Steric hindrance explanation?

Answer 11

In the Sn2 mechanism there are 4 atoms, or groups of atoms surrounding the central C atom as the Nucleophiles approaches. The attacking nucleophiles has to get close to the central atom. If the groups of atoms surrounding the central atom are large, then they will physically block the central atom.

Question 12

Which mechanism will primary haloalkanes have?

Answer 12

Sn2

Question 13

Which mechanism will tertiary haloalkanes have?

Answer 13

Sn1