U3-3-5 - Alkenes

Question 1

Alcohols can be dehydrated using ____________ to catalyse the reaction.

Answer 1

hot Al₂O₃ or conc. H₂SO₄ or H₃PO₄

Question 2

Name this type of reaction

Answer 2

Elimination/dehydration

Question 3

Which is the major product?

Answer 3

But-2-ene

Question 4

How do you turn a haloalkane into an alkene?

Answer 4

React with ethanolic KOH or NaOH.

(NOT aqueous or you’ll make an alcohol)

Question 5

Name this type of reaction

Answer 5

(Electrophilic) addition

Question 6

Why does the Br₂ molecule become polarised (acquire partial charges)?

Answer 6

The e⁻ rich C=C bond pushes away the e⁻ in Br₂ to one side (one Br), making one Br^δ+ and one Br^δ−.

Question 7

Step 1 of alkene halogenation

Answer 7

Question 8

Step 1 of alkene halogenation

Answer 8

Question 9

Step 2 of alkene halogenation

Answer 9

Question 10

Alkene + hydrogen halide

Answer 10

Question 11

Alkene + hydrogen halide

Answer 11

Question 12

Why is 2-bromopropane the major product (and not 1-bromopropane)?

Answer 12

More stable carbocation formed