Chapter 8.2 - Alkenes

Question 1

Alkene molecular formula?

Answer 1

CnH2n

Question 2

Properties of alkenes

Answer 2

Formula CnH2
More reactive
Unsaturated
Double bond present
Non polar and hence does not dissolve in water
Angle of the bonds around the carbon are 120°

Question 3

Alkenes can demonstrate structural isomerism and ‘cis -trans’ (geometric) isomerism

Answer 3

The atoms in the alkene isomers are joined in the same order but have different arrangement in space.

This occurs because the atoms associated with a carbon-carbon double bond are fixed in position

2 atoms joined by a single bond can rotate freely around the single bond

2 atoms joined by a double bond do not rotate freely because the double bond locks the atoms firmly in position

Question 4

Cid- trans/ geometric isomers can occur when there are two different groups attached to each carbon atom involved in the double bond

Answer 4

Cis - the same group on each carbon is located on the same side of the double bond

Trans - the same group on each carbon is located on opposite sides the double bond

Question 5

How to name Alkenes?

Answer 5

1. Identify Longest branch of chain with the location of double bond Eg. Hex-2-ane
2. Number carbon atoms to give smallest double bond of carbon
3. Alkyl groups
4. List Position of alkyl groups
5. Two identical chains present use di or tri
6. Cis or trans

Question 6

What does unsaturated mean?

Answer 6

Carbon atoms are not bonded to the maximum number of atoms they can be

Question 7

Why are alkenes unsaturated

Answer 7

2 Atoms can join onto 1/2 of the carbon double bond when it opens up
Therefore it has the potential to have spare bonds to link up with other atoms

Alkenes have two were hydrogen atoms than alkanes