Alkenes

Question 1

How can alkenes be prepared?

Answer 1

• Dehydration of alcohols

- Base induced elimination of hydrogen halides from monohalogenoalkanes.

Question 2

How may alkenes be dehydrated?

Answer 2

Passing the vapour of an alcohol over hot aluminium oxide

Treating the alcohol with concentrated sulphuric acid or concentrated phosphoric acid.

Question 3

What is removed during dehydration?

Answer 3

An OH group and an H from the adjacent carbon, the hydrogen is usually removed from the carbon with least hydrogens.

Question 4

What is an elimination reaction?

Answer 4

When the elements of a simple molecule are removed from the organic molecule and not replaced.

Question 5

Why is concentrated phosphoric acid preferred to concentrated sulphuric acid?

Answer 5

With sulphuric acid, more side reactions occur and it tends to lead to charring

Question 6

How is base-induced elimination of hydrogen halides from monohalogenoalkanes achieved?

Answer 6

By heating under reflux with ethanol potassium hydroxide ( a solution of potassium hydroxide in ethanol)

Question 7

Why is the reaction referred to as base-induced elimination?

Answer 7

Because it tis the presence of the presence of the base which drives the reaction.

Question 8

What are the 4 types of addition reactions alkenes can undergo?

Answer 8

Hydrogenation —-> Alkanes
Halogenation—-> Dihaloalkanes
Hydrohalogenation—-> Hydrogen Halides
Hydration—–> Alcohols

Question 9

What does Maokovnikov’s rule state?

Answer 9

The hydrogen atom adds to the carbon of the double bond with the larger number of hydrogen atoms already attached.