Chapter 15 Haloalkanes

Question 1

what is the general formula of a haloalkane

Answer 1

CnH2n+1X

Question 2

what is the functional group of a haloalkane

Answer 2

any halogen attached to a carbon

Question 3

give the three examples of substitution reactions haloalkanes can undergo

Answer 3

haloalkane + hydroxide ions or water –> alcohol
haloalkane + nitride ion –> nitrile (R-CN)
haloalkane + ammonia –> amine (R-NH2)

Question 4

what two factors does the rate of reaction involving a haloalkane depend on

Answer 4

bond strength

primary,secondary or tertiary carbon

Question 5

what does the mechanism of a reaction involving a haloalkane depend on

Answer 5

bond polarity

Question 6

describe the reaction of a haloalkane and hydroxide ions

Answer 6

> the OH- is attracted to the slightly positive carbon

>the OH- breaks the C-X bond making an alcohol and X-

Question 7

what type of reaction is the haloalkane + OH-

Answer 7

one step nucleophilic substitution

Question 8

what are the reaction conditions required for the reaction of haloalkane + OH-

Answer 8

reflux

source of OH- like NaOH

Question 9

describe the reaction of haloalkane + water

Answer 9

> the water molecule is attracted to the carbon due to charge breaking the X out making X-
the oxygen is now unstable because it is bonded to too many other atoms so kicks out one of the hydrogens
The H+ then bonds to the X- making an alcohol and hydrogen halide

Question 10

what type of reaction is haloalkane + water

Answer 10

two step nucleophilic substitution

Question 11

describe the reaction haloalkane + CN-

Answer 11

> both the carbon and the nitrogen in the CN- have a lone pair so both can bond the the slightly positive carbon breaking the C-X bond and making C-CN and X-

Question 12

describe the reaction of haloalkane + ammonia

Answer 12

> the NH3 has a lone pair so is a nucleophile and is attracted to the carbon breaking the C-X bond
the nitrogen is now bonded to too many atoms so gets rid of one the hydrogens
The H+ and X- bond to form a hydrogen halide

Question 13

what type of reaction is haloalkane + ammonia

Answer 13

2 step nucleophilic substitution

Question 14

why does the haloalkane + ammonia reaction take place in a sealed tube with the ammonia in a gaseous state

Answer 14

to avoid the ammonia having to compete with water reducing yield

Question 15

give two uses for CFCs

Answer 15

making polymers
solvents
aerosols
refrigerants
flame retardants

Question 16

what are the four pros of CFCs

Answer 16

polar bonds so mix in solvents
non toxic
non flammable
high bond enthalpy

Question 17

what is the con of CFCs

Answer 17

catalyse the depletion of ozone layer

Question 18

what is the ozone molecule

Answer 18

O3

Question 19

what is the ozone layer

Answer 19

layer at the top of the stratosphere made up of gases including ozone

Question 20

what does ozone do

Answer 20

it absorbs high energy UVB radiation from the sun

Question 21

why is UVB dangerous

Answer 21

it can cause skin cancer, wrinkles and cataracts

Question 22

what are three ozone cycle reactions

Answer 22

O3 + UVB –> O2 + O•
O2 + UVB –> 2O•
O• + O2 –> O3

Question 23

what type of mechanism is the ozone layer reaction

Answer 23

homolytic bond fission

Question 24

why do CFCs deplete ozone

Answer 24

> they are very stable at unreactive at the troposphere level but they break apart at the ozone layer due to the high energy UVB
this produces a chlorine radical that catalyses the depletion of ozone

Question 25

what are the equation for the depletion of ozone due to CFC

Answer 25

Cl• + O3 –> •ClO + O2

•ClO + •O –> Cl• + O2

Question 26

what are the Cl• and •ClO in the ozone depletion reactions

Answer 26

• Cl is a catalyst so isn’t used up and is chemically unchanged
• ClO is an intermediate

Question 27

what other radical can lead to the depletion of ozone

Answer 27

NO• from aircraft

Question 28

why aren’t NO radicals as dangerous as Cl radicals

Answer 28

normally the reactions to make the NO radicals take place lower down in the atmosphere at the cruising altitude of planes