DF6- Alkenes

Question 1

Define Alkene

Answer 1

Unsaturated hydrocarbon

Question 2

Give general formula of alkenes

Answer 2

CnH2n

Question 3

What are the steps you take when naming alkanes/alkenes?

Answer 3

1. Identify longest chain
2. Identify any side chains, name these according to number of carbons
3. State location of side chains with number as prefix
4. ALKENES ONLY identify position of double bond, number goes in middle of longest chain

Question 4

How is the sigma bond formed in C=C double bond?

Answer 4

• it is the overlap of s-orbitals

- direct, head on bond containing shared pair of electrons

Question 5

How is Pi bond formed in C=C double bond?

Answer 5

• p-orbitals overlap above and below carbons

- contain shared pair of electrons, which could be in either orbital

Question 6

Define electrophile

Answer 6

Substance with partial positive charge that is attracted to region that is negatively charged

Question 7

Why is the double bond in alkenes susceptible to attacks by electrophiles?

Answer 7

• region of high electron density, therefore negatively charged

Question 8

Describe basic mechanism of eletrophilic addition with Br

Answer 8

1. Br becomes polarised as it approaches negative double bond
2. Electrons in Br are repelled by electrons in double bond, move further down molecule
3. Electrons in double bond move to partially positive Br, Pi bond breaks and forms bond with 1 Br atom
4. Carbocation is formed, quickly forms bond with Br ion

Question 9

Define carbocation

Answer 9

An ion with positively charged carbon atom

Question 10

What conditions does hydrogenation (addition of hydrogen) to alkene require?

Answer 10

• nickel catalyst

- 150 degrees Celsius

Question 11

What conditions does addition reaction between alkene and water (steam) require?

Answer 11

• sulphuric acid catalyst

- high temp and pressure

Question 12

What is produced when an alkene reacts with water?

Answer 12

Alcohol