Topic 7:Alkenes

Question 1

Structure of alkenes

Answer 1

Planar

All bonding pairs on carbon have 120 degree angles

Question 2

Geometrical isomers

Answer 2

Occurs around C–C bonds

Due to the fact that the species around the carbon can’t move

Question 3

Stereoisomers

Answer 3

Compounds with the same structural formula but different arrangements of bonds in 3D space

Question 4

Physical properties of Alkenes

Answer 4

• Van der waals are the only intermolecular forces
• Similar properties to those of alkanes
• Melting and boiling point increases with number of C atoms present

Question 5

Positive inductive effect

Answer 5

The more alkyl groups attached the more stable the molecule is

Question 6

Explanation of halogens reacting with alkenes (electrophilic) addition

Answer 6

• At any one time a diatomic halogen could form a temporary dipole
  This positive charge is attracted to the electron dense double bond in the alkene
• This negativity also repels the electrons in the Br2, causing it to become more electronegative
• Same process of nucleophilic addition occurs

Question 7

Test for alkenes

Answer 7

Add a few drops of bromine water

Will turn orange to clear colourless

Question 8

Alkene (steam conditions) to alcohol

Answer 8

300 degrees
Phosphoric acid catalyst
60-70 ATM pressure

Question 9

Why are addition polymers unreactive?

Answer 9

• They are large saturated alkanes
• They have strong covalent bonds
• They are non- polar

Question 10

Why do polymers have a low boiling/ melting point

Answer 10

They only contain Van der Waals

They can sometimes have side chains

Question 11

PVC (normal) uses

Answer 11

Plastic bags
Sheeting
Insulation of electrical cables

Question 12

Hardened PVC uses

Answer 12

• Milk crates
• Buckets
• Bottles

Question 13

Plasticised PVC

Answer 13

• Push molecules apart
• Intermolecular forces are weaker
• Layers can slide over each other more easily

Question 14

Hardened PVC

Answer 14

• Pulls the molecules closer together
• Stronger intermolecular forces
• Molecules can’t slide over each other

Question 15

Which type of E/Z isomerism is more stable

Answer 15

E isomerism