Alkenes

Question 1

How are alkenes named?

Answer 1

identify longest chain
follow prefix with ‘ene’
insert number before ‘ene’

Question 2

What are the bonds in alkenes?

Answer 2

Double bond which is sp2 hybridised.

Question 3

What are the physical properties of trans-alkenes?

Answer 3

higher melting points than cis isomers

lower boiling points

Question 4

What is hydrogenation and what conditions are required for it to take place?

Answer 4

Hydrogenation is the reaction of water with ethene producing ethanol.

requires platinum/nickel catalyst and high temperature+pressure.

Question 5

What does markovnikoff’s rule state?

Answer 5

the nucleophile will be bonded to the most substituted carbon (i.e the fewest hydrogens attached in the product)

Question 6

How can oxidation occur in alkenes?

Answer 6

using potassium permanganate (KMnO4) under mild conditions, a glycol can be produced
(e.g oxidation of ethene
Ethene + KMnO4 => Ethylene glycol)

using potassium permanganate (KMnO4) under abrasive conditions leads to oxidative cleavage of C=C bond
(e.g oxidation of 2-butene
2-butene + KMnO4 => acetate ion => acetic acid)

Question 7

What are the steps in electrophilic addition in alkenes?

Answer 7

Bromine polarised by alkene to become electrophile.
The electrophile reacts with C=C leaving a carbocation & a bromine ion
Bromine ion gives pair of electrons to cation to form C-Br bond.

Question 8

What is a carbocation?

Answer 8

A carbocation is an ion with positively charged carbon atom

Question 9

What is an electrophile?

Answer 9

Electrophile is a positive ion/molecule that can accept lone pair of electrons to form a covalent bond