Haloalkanes

Question 1

What is the functional group for a haloalkane?

Answer 1

a halogen atom

Question 2

What is the state of haloalkanes at RMT?

Answer 2

gas

Question 3

why do the BP increase as the no. of C atoms increase?

Answer 3

theres an increases in surface contact area between molecules which means an increase in london forces so more energy is needed to break them

Question 4

Why are haloalkanes insoluble in water?

Answer 4

cannot form H bonds

Question 5

What type of reaction is a reaction of an alkane and a halogen?

Answer 5

radical substitution

Question 6

What is the overall equation of radical substitution?

Answer 6

CH3CH3 + Br2 —-> CH3CH2Br + HBr

Question 7

Why is radical substitution not a good way of making a haloalkane?

Answer 7

more than one H atom can be substituted and in different positions
so a mixture of products is formed with a low % yeild of the desired product

Question 8

What 3 ways can a haloalkane be made?

Answer 8

radical substitution
electrophilic addition
alcohol and hydrogen halide

Question 9

Why is electrophillic addition more efficient than radical substitution?

Answer 9

100% atome economy
only 1 or 2 possible products formed

Question 10

What are the conditions of reacting an alcohol with a hydrogen halide?

Answer 10

warm the alcohol with a mixture of the NaX
concentrated H2SO4 catalyst

Question 11

What are the conditions of nucleophilic substitution?

Answer 11

heating the mixture with aq sodium hydroxide

Question 12

What is the overall equation for nucleophilic substitution?

Answer 12

CH3CH2Br + OH- —-> CH3CH2OH + Br-

Question 13

What is a nucleophile?

Answer 13

an electron pair donor

Question 14

What are the key points to include when drawing the nucleophilic sub mechanism?

Answer 14

curly arrow from lone pair on :OH- to C attached to halogen
dipoles on C-Br bond
curly arrow from C-Br bond to Br
:Br- product

Question 15

What type of bond breaking is present in nucleophilic subsitution?

Answer 15

heterolytic fission of the carbon-halogen bond

Question 16

What is the trend of the rate of hydrolysis of the haloalkanes?

Answer 16

ROR increases down the group

Question 17

Why does the ROR of hydrolysis increase down the group?

Answer 17

bonds get weaker going down the group so theres a lower activation energy and a faster reaction

Question 18

What is the exprt. used to investigate the ROR of hydrolysis?

Answer 18

add ethanol and aq silver nitrate to each haloalkane
warm the tubes in the same hot water bath - same temp
observe the rate the precipitate forms

Question 19

Why is ethanol used in the hydrolysis expt.?

Answer 19

to act as a solvent - allows water and haloalkanes to mix and produce a single solution rather than two layers

Question 20

What are the 2 successive reactions that occur in the hydrolysis expt.?

Answer 20

each organic compound reacts with water:
C2H5X +H2O —> C2H5OH + H+ + X-

the halide ions released react with the silver ions:
Ag+ (aq) + X- (aq) —-> AgX (s)

Question 21

What are the common uses of chlorofluoroalkanes?

Answer 21

solvents
aerosol propellants

Question 22

How are CFCs harmful to the envrionment?

Answer 22

they cause damage to the ozone layer

Question 23

Why is ozone important for the atmosphere?

Answer 23

it absorbs UV radiation from the sun, which could cause mutations if it reached the surface

Question 24

What is the reaction with CF2Cl2 forming Cl radicals?

Answer 24

CF2Cl2 –UV—> CF2Cl. + Cl.

Question 25

How do the Cl radicals break down the ozone molecules?

Answer 25

they act as a catalyst, breaking them down in a chain reaction
the radicals are used up then regenerated

Question 26

What are the chain reactions of cl radicals breaking down ozone?

Answer 26

Cl. + O3 —-> ClO. + O2
ClO. + O —> Cl. + O2

Question 27

What is the overall reaction of ozone being broken down?

Answer 27

O3 + o —> 2 O2

Question 28

What are the chain reactions of nitrogen oxide breaking down ozone?

Answer 28

.NO + O3 —> .NO2 + O2
.NO2 + O—-> .NO + O2

Question 29

How do nitrogen oxides form?

Answer 29

form naturally as a result of lightning acting on nitrogen and oxygen in the air

Question 30

How is the amount of nitrogen oxide produced increased in higher altitude?

Answer 30

by the effect of jet aeroplane engine - the intense heat

Question 31

What are 3 examples of nucleophiles?

Answer 31

hydroxide ions
water molecules
ammonia molecules

Question 32

What happens during hydrolysis of a haloalkane (nucleophilic substitution)?

Answer 32

1. OH nucleophile approaches carbon atom attached to halogen
2. the lone pair on the OH ion is attracted and donated to the delta+ carbon atom
3. a new bond is formed between the oxygen atom and the carbon atom
4. the carbon-halogen bond breaks by heterolytic fission
5. alchohol and halide ion formed

Question 33

Why does the hydroxide nucleophile in hydrolysis, approach from the opposite side of the halogen?

Answer 33

minimises the repulsion between nucleophile and the delta- halogen atom

Question 34

What base is used to make alchohols from haloalkanes?

Answer 34

sodium hydroxide

Question 35

what is the trend of C-X bond enthalpies down group 2?

Answer 35

bond enthalpy decreases down group 2

Question 36

What is the link between bond enthalpies and ROR?

Answer 36

the compound with the slowest ROR is the one with the strongest carbon-halogen bond

Question 37

What are organohalogen compounds?

Answer 37

molecules that contain at least one halogen atom joined to a carbon chain