organic chem; alkenes

Question 1

Alkenes are…

Answer 1

Unsaturated hydrocarbons

Question 2

Alkenes general formula

Answer 2

CnH2n — only applies to alkenes with 1 double bond

Question 3

What type of reaction do alkenes undergo?

Answer 3

Addition reactions

Question 4

State whether or not alkenes are reactive & why

Answer 4

Are reactive
As their double bond have a high electron density

Question 5

An electrophile is…

Answer 5

An e- pair acceptor — are deficent in e-, this attracts them to double bonds

Question 6

Examples of electrophile ions

Answer 6

• NO2+
• H+

Question 7

Examples of polar electrophiles

Answer 7

• HBr
• H2SO4

Question 8

Test for Alkenes

Answer 8

Addition of Bromine — decolouration of Br water

Question 9

Explain how alkenes are tested

Answer 9

1. Add Br water to an alkene
2. Observe colour change from brown-orange to colourless

Question 10

Explain addition of bromine in terms of electrons

Answer 10

Br (orange/brown) is the electrophile and adds to the alkene forming a dibromoalkane (colourless)

Question 11

Alkenes + Hydrogen Halides = …

Answer 11

Halogenoalkanes

Question 12

What does reacting hydrogen halides with unsymmetrical alkenes produce?

Answer 12

2 different products

Question 13

What are the products determined by?

Answer 13

The stability of the carbocarion intermediate — the more alkyl groups bonded to the carbocation = the more stable the intermediate is

Question 14

Why does more bonded alkyl groups stablise carbocations?

Answer 14

As alkyl group push e- towards the +ve carbocation which stablises it

Question 15

Which carbocation is the most stable: primary, secondary or teritairy?

Answer 15

Teritiary

Question 16

What type of product is likely to form in an addition reaction of hydrogen halides?

Answer 16

Secondary carbocation will be the major product — as its more stable, its more likely to be produced

Question 17

Alkenes + Sulfuric Acid = …

Answer 17

Alkyl hydrogen sulfates

Question 18

What is added to sulfuric acid to form alkenes?

Answer 18

Alcohol

Question 19

Draw the mechanism of additon of sulfuric acid

Question 20

Alkyl hydrogen sulfates can be … to alcohols

Answer 20

reformed

Question 21

How is ethanol formed from alkyl hydrogen sulfates?

Answer 21

Adding cold water to warm ethyl hydrogen sulfate form ethanol — through hydrolysis reaction

Question 22

Alkenes are … which join to form …

Answer 22

…monomers
…addition polymers

Question 23

Polymers can be … or …

Answer 23

…natural
…synthetic

Question 24

Poly(alkenes) are … molecules

Answer 24

… saturated — usually non-polar = unreactive

Question 25

As polyalkenes chains are non-polar they only have … between the chains

Answer 25

…VDWs

Question 26

What increases the VDWs in a polyalkene?

Answer 26

The length of the chain

Question 27

Properties of shorter polyalkenes

Answer 27

Have more branches More flexible & weaker

Question 28

Polymers with little … & long tend to be more … & …

Answer 28

…branching …rigid …stronger

Question 29

What do plasticisers do to polymers?

Answer 29

Make polymers more flexible by sliding between polymer chains & pushing them apart — this weaken VDWs