6. reactions of alkenes

Question 1

what reactions happen to alkenes

Answer 1

electrophilic addition (dihaloalkane)
hydrogenation (addition reaction) (alkane)
steam hydration (alcohol)

Question 2

during electrophillic addition reaction of an alkene what happens

Answer 2

double bond opens up

atoms added to carbon atoms

Question 3

why do elecrophilic addition ractions happen to alkenes

Answer 3

double bond has lots of electrons and is easily attacked by electrophiles

Question 4

what are electrophiles

Answer 4

electron-pair acceptors

usually short of electrons so attracted to electron rich areas

Question 5

what do electrophiles include

Answer 5

positivley charged ions e.g. H+ and NO2+

polar molecules. atoms with positive dipole attracted toelectron rich areas

Question 6

alkenes undergo hydrogenation to produce

Answer 6

alkanes

Question 7

hydrogenation

1. ethene reacts with ? to produce ?
2. equation
3. conditions

Answer 7

1. hydrogen gas to produce ethane
2. CH2CH2 + H2 -> CH3CH3
3. nickel catalyst

Question 8

electrophilic addition

1. alkenes can react with halogens to form ?
2. equation

Answer 8

1. dihaloalkanes

2. CH2CH2 + X2 -> CH2XCH2X

Question 9

what is a carbocation

Answer 9

an organic ion containing a positively charged carbon atom

Question 10

how is bromine water used to test for Carbon carbon double bond

Answer 10

shake alkene with orange bromine water = solution decolourises
(bromine is added across double bond to form a colourless dibromoalkane)

Question 11

steam hydration

1. alkenes reacts with steam to make ?
2. equation
3. conditions

Answer 11

1. alcohols
2. CH2CH2(g) + H2O(g) CH3CH2OH(g)
3. phosphoric (v) acid catalyst

Question 12

steam hydration

1. reaction yield high/low?
2. is this a problem?

Answer 12

1. low.

2. no. can recycle unreacted alkene gas

Question 13

addition with hydrogen halides

1. alkenes react with hydrogen halides to make ?
2. equation

Answer 13

1. haloalkanes.

2. CH2CH2 + HBr -> CH2BrCH3

Question 14

markownikoffs rule

Answer 14

major product from addition of a hydrogen halide (HX) to an unsymmetrical alkene is one where H adds to the carbon with most Hs already attached

Question 15

adding hydrogen halides to unsymmetrical alkenes

1. what does the amount of each product formed depend on
2. what carbocations are most stable and why
3. which carbocation is most likely to form

Answer 15

1. how stable the carbocation formed in the middle of the reaction
2. carbocations with more alkyl groups because alkyl groups feed electrons towards positive charge.
3. the more stable carbocation