Alkenes

Question 1

What does the C=C consist of in Alkenes

Answer 1

A Pi bond and a sigma bond

The Pi bond is a sideways overlap of P-Orbitals above and below the bonding C atoms.
The sigma bond is the overlap of orbitals directly between the bonding atoms.

Question 2

What is the shape and bond angle around the each carbon in the C=C bond?

Answer 2

1. Three bonding pair regions which repel each other as far as possible leading to a trigonal planar shape with angle of 120 degrees.

Question 3

What qualifies a molecule to have E/Z isomerism?

Answer 3

1. A C=C bond
2. There are two different groups attached to the carbon in the C=C.

Question 4

When is an alkene classed as cis?

Answer 4

Both hydrogen atoms are on the same side

Question 5

When is an alkene Trans?

Answer 5

when Bothe hydrogen atoms are on opposite sides

Question 6

How do we classify alkenes as E/Z?

Answer 6

The atom with the greatest atomic number has the highest priority

A Z isomer has both higher priority groups on the same side

an E isomer has the higher priority groups on opposite sides.

Question 7

Define an Electrophile

Answer 7

An electron pair acceptor

Question 8

Alkenes + Hydrogen —–> ? and what are the conditions?

Answer 8

——-> Alkanes

Nickel catalyst and 150 degrees

Question 9

Alkenes + Halogens ——->?

Answer 9

Dihaloalkanes

Question 10

How do you test for Unsaturation (contains double bonds)?

Answer 10

Orange bromine water is added to an excess of an organic compound, turning it colourless.

Question 11

Alkenes + H2O (steam) ——–> ?
Conditions?

Answer 11

Alcohols

Concentrated phosphoric acid (H3PO4)

With an unsymmetrical alkene, two products are possible.

Question 12

Alkenes + HBr———> ?

Answer 12

——> Bromoalkanes

Question 13

What happens when alkenes react with HBr in symmetrical and unsymmetrical alkenes?

Answer 13

In symmetrical alkenes only 1 product can be formed for example with Ethene, it doesn’t matter which way round the Br is the product will be the same.

In unsymmetrical alkenes, propene, two products can be formed either 1 - bromoporpane or 2-Bromopropane.

Question 14

How does the bond in the dipole break in electrophilic addition?

Answer 14

By heterolytic fission- breaking of a covalent bond where one atom receives both electrons from the bonded pair.

Question 15

What is the difference between primary, secondary and tertiary carbocations?

Answer 15

A primary carbocation is where the carbocation involved only has one carbon directly attached to it
Secondary is when it’s directly attached to two, tertiary is when it’s directly attached to three