ELECTROPHILIC ADDITION

Question 1

What are alkenes? (1)

Answer 1

They are unsaturated hydrocarbons, they have at least one double bond.

Question 2

Why are alkenes unsaturated? (1)

Answer 2

Molecules with carbon double bonds are unsaturated because they can make more bonds with extra atoms in addition reactions.

Question 3

What makes alkenes have a high electron density? (1)

Answer 3

Because there are two electrons in the double bond, this makes alkenes reactive.

Question 4

What happens in electrophilic addition? (2)

Answer 4

1) the double bonds open up and atoms are added to the carbon atoms
2) these reactions occur because the double bond has got plenty of electrons and is easily attacked by electrophiles.

Question 5

What are electrophiles? (1)

Answer 5

Electrophiles are electron acceptors - they are usually short of electrons, so there attracted to places where there are lots of them.

Question 6

What are some examples of electrophiles? (2)

Answer 6

-positively charged ions e.g H+ and NO2+
-polar molecules

Question 7

What test is used to detect insaturation? (1)

Answer 7

We use bromine water.

Question 8

What colour does bromine water turn if the test is positive? (1)

Answer 8

From orange to colourless.

Question 9

What is the mechanism for adding bromine water to an alkene? (1)

Answer 9

H2C=CH2 + Br2. -> CH2BrCH2Br

Question 10

What is a carbocation? (1)

Answer 10

A carbocation is an organic ion containing a positively charged carbon atom

Question 11

What are the nucleophiles that can be added in electrophilic addition reactions? (3)

Answer 11

-a molecule of bromine
-hydrogen halides
-cold concentrated sulfuric acid

Question 12

What are the products from an electrophilic addition reaction with a hydrogen halides? (1)

Answer 12

Forms a halogenoalkane

Question 13

What are the two possible products when a hydrogen halide reacts with an unsymmetrical alkene? (2)

Answer 13

-can form two of; a primary, secondary or tertiary carbocation

Question 14

What is the carbocation intermediate?

Answer 14

The amount of each product formed depends on how stable the carbocation formed in the middle of the reaction is

Question 15

What carbocation is most stable?

Answer 15

Carbocation with more alkyl groups are more stable because the alkyl groups feed electrons towards the positive charge, the more stable carbocation is more likely to form.

Question 16

What are the products of a electrophilic addition reaction when the alkene reacts with cold concentrated sulfuric acid? (1)

Answer 16

Form alkyl hydrogen sulfates

Question 17

What can alkyl hydrogen sulfate be converted to? (1)

Answer 17

Formed into alcohols

Question 18

What happens in an electrophilic addiction reaction with cold concentrated sulphuric acid? (3)

Answer 18

1) cold concentrated sulphuric acid reacts with an alkene in an electrophilic addition reaction
2) if you then add cold water and warm the product, it hydrolyses to form an alcohol
3) the sulphuric acid is not used up, it acts as a catalyst