mechanism of haloalkanes

Question 1

what is the general idea on how haloalkanes are formed?

Answer 1

when you mix haloalkanes and halogens in the present of uv light

Question 2

why do halogens do not react with alkanes in the dark

Answer 2

It requires UV light to form halogens into free radicals which are free to act as nucleophiles in a reaction.

Question 3

What are the steps in a chain reaction

Answer 3

initiation, propagation. and termination.

Question 4

Initiation

Answer 4

• The first step is initiation, this reaction is breaking the Cl-Cl bond to form two chlorine atoms.

Question 5

hetolytic fission

Answer 5

when one compoment takes both electrons of the covalently bonded molecule forms ions

Question 6

homolytic fission

Answer 6

both elements take an electron. radicals

Question 7

why does the c–h bond does not break in present of UV light

Answer 7

bond in the alkanes needs more energy to break than is

available in ultraviolet radiation, so this bond does not break.

Question 8

how many steps does propagation has

Answer 8

2

Question 9

first step of propagation

Answer 9

The chlorine free radical takes a hydrogen atom from methane

ch3 radical
hcl molecule

Question 10

second step of prorogation

Answer 10

The methyl free radical is also very reactive and reacts with a chlorine molecule.
ch3cl and cl radical

Question 11

termination of haloalkane synthesis

Answer 11

either
two chlorine radicals
two methyl radicals
methyl and chlorine radical

Question 12

other products of progation

Answer 12

Dichloromethane may be made at the propagation stage, if a chlorine radical reacts with some chloromethane that has already formed.

Question 13

why can haloalkane isomers may be formed with longer chain isomers

Answer 13

because the Cl• can replace any of the hydrogen atoms.

Question 14

why are chain reactions not ideal

Answer 14

it creates a mixture of products

Question 15

why are CFCS important

Answer 15

chloronurorocarbons (CFCs) in the stratosphere are

destroying the ozone layer.

Question 16

what is the ozone layer

Answer 16

a layer that has 03

Question 17

How do CFCS destroy the atmosphere

Answer 17

in present of uv light in atmosphere it forms cl radicals these radicals react with oxygen to form 03 and catalyes the breakdown of the ozone layer

Question 18

why is the destruction of the ozone layer an issue

Answer 18

if uv is not absorbed by ozone layer it will absorb the earth and life on earth. this could lead to;
damage dna - cancer
kill plantlon etc which destroys food chain

Question 19

CFCS purposes

Answer 19

coolants in fridges
polymers
propellants

Question 20

general haloalkane formula

Answer 20

2n+1 and halogen

Question 21

example of haloalkane

Answer 21

1,1,1,2-tetrachloroethane

Question 22

bond polarity of haloalkanes

Answer 22

This bond is polar.
because halogens are more electronegative than carbon. This means that it attracts the shared electrons more so it becomes more electron dense and delta negative than the carbon

Question 23

why are haloalkanes INSOLUBLE in water

Answer 23

• they can’t form hydrogen bonds,

and the energy required to break hydrogen bonds in water is higher than the energy released when new bonds between the haloalkane and water are formed

Question 24

boiling point of haloalkanes

Answer 24

increases down the periodic table

increases as chain gets longer

Question 25

increases down periodic table

Answer 25

electron number increases. This means that the van der waal forces are stronger so more energy is required to break the bonds

Question 26

chain length

Answer 26

more electrons

more surface for van der waals forces to act on.

Question 27

why is c-f bonds strongest and least reactive

Answer 27

f is the smallest atom.
less shielding.
closer to nucleus
requires more energy to break bond

Question 28

what is nucleophile

Answer 28

a reagant with two lone pair electrons that donates the lone pair of electron and forms a bond with a partially postively charge carbon.

Question 29

nucleophiles that I learnt about

Answer 29

the hydroxide ion. -:oH
• ammonia, :NH3
• the cyanide ion, -:CN.

Question 30

name of mechanism

Answer 30

nucleophilic substitutions

they replace the halogen on haloalkane

Question 31

what does curly arrow mean

Answer 31

electrons are being donated

Question 32

what are electrons attracted to

Answer 32

partially postive carbon

Question 33

what is a radical

Answer 33

highly reactive species with one single unpaired electron.

Question 34

photochemical reaction

Answer 34

a reaction that is initiation by absorbing light energy

Question 35

chain reaction

Answer 35

when products yield initiated more reacts to form more products