3.3.3 Halogenoalkanes

Question 1

what are halogenoalkanes?

Answer 1

an alkane with a halogen atom attached to it

Question 2

why are most carbon-halogen bonds polar

Answer 2

halogens are more elctronegative than carbon

Question 3

what are some of the uses of a halogenoalaknes?

Answer 3

-refrigerants
-solevents used in pharmacetuicals

Question 4

why has the use of halogenoalkanes been restricted

Answer 4

due to the effect of chlorofluorocarbons on thee atmosphere

Question 5

what is a nucleophile

Answer 5

an electron-pair donor

Question 6

why is the carbon atom delta positive

Answer 6

it doesnt have enough electrons

Question 7

what does the nucleophile do

Answer 7

donates an electron pair to somewhere which doesnt have enough electrons
e.g. carbons

Question 8

what does the nucleophile attack

Answer 8

the delta positive carbon

Question 9

what are the 3 nucleophiles that undergo subsitiution reactions

Answer 9

• CN-
• NH3
• OH-

Question 10

name the 3 nucleophiles that undergo substitution reaactions

Answer 10

-cyanide ion
-ammonia
-hydroxide ion

Question 11

what is meant by nucleophilic substitution

Answer 11

the nucleophile attacks the cabon which is less dense compared to the halogen.
it replaces the halogen group
the halogen group becomes the product of the reaction

Question 12

what are the conditions for the nucleophilic substituition of the hydroxide ions

Answer 12

-warm aqueous sodium hydroxide
-under reflux

Question 13

what reagent is used for the nucelophilic substitution of the hydroxide ions

Answer 13

WARM aqueous sodium hydroxide

Question 14

cheekyy

where does the 2nd arrow go from during the nucleophilic substituition

Answer 14

from the bond to the halogen

Question 15

what conditions are needed for the nucleopilic substituitoin of cyanide ions

Answer 15

• WARM ethanolic potassium cyanide
  -under REFLUX

Question 16

what reagent is used in the nucleophilic substituition of cyanide ions

Answer 16

-ethanolic potaassium cyanide

Question 17

what does the reaction with cyaninde ions produce

Answer 17

nitriles

Question 18

whaat does the reaction with hydroxides produce

Answer 18

alcohols

Question 19

what are conditions for the nucleophilic substituition of ammonia

Answer 19

Heated with ethanolic ammonia
in EXCESS

Question 20

why is there excess ethanolic ammonia

Answer 20

so it cant as a base
for additional reactiosn

Question 21

why does the excess ammonia act as a base

Answer 21

cause in the intermediate the nitrogen has 4 bonds and this needs to be removes
-so that it will have 3 bonds

Question 22

what does the reaction with ammonia produce

Answer 22

amines

Question 23

what direction does the arrow go when the intermediate is attacked by the base

Answer 23

from the bond to the nitogrn

Question 24

explain the trend in bond enthalpies for the C-halogen bond

Answer 24

as the bond enthalpy decreases it bcomes more reactive

Question 25

out of all the C-halogen bonds what is the most reactive element

Answer 25

C-I

Question 26

why is C-I the most reactive

Answer 26

it has the lowest bond enthalpy

Question 27

what are the products of the elimination reaction

Answer 27

an alkene

Question 28

what are the conditions in the elimination reaction

Answer 28

warm ethanolic sodium hydroxide under reflux

Question 29

where does the arrow go to from the hydroxides in the elimination reactions

Answer 29

to the adjacent hydrogen off the carbon with the halogen

Question 30

how doe we know wether the hydroxide is going to undergo a elimination or substitution reacttion

Answer 30

the solevent

Question 31

explain the difference the hydroxides in the elimaination and substiution reactions

Answer 31

elimination- ethanolic sodium hydroxides substitution- dilute sodium hydroxide

Question 32

what are chloroflurocarbons used for

Answer 32

solvents refridgenats- fridges propellants- deodarants

Question 33

what do chloroflurocarbons do

Answer 33

they break down ozone (O3) in the atmosphere

Question 34

State the benefit to life on Earth of ozone in the upper atmosphere.

Answer 34

absorbs harmful ultraviolet rays

Question 35

# that eq u did State the benefit to life on Earth of ozone in the upper atmosphere.

Answer 35

-absorbs infrared radiation - due to molecules having polar bonds

Question 36

explain what enables CFs to break the ozone

Answer 36

because of the UV rays in the atmosphere which breaks the C-Cl bonds and forms free radicals

Question 37

what do the free radicals do when they are broken by UV radiations

Answer 37

they catalyse the break down of ozone .Cl

Question 38

explain why the C-Cl bonds break the easiets compared to the C-F bonds

Answer 38

- bonds are easier to break because it has the lowest bond enthalpy compared to the C-F bonds

Question 40

outline the direction of the arrows in the elimination reaction

Answer 40

the hydroxides attack the adjacent hydrogen that has the halogen bonded to it the bond breaks from that hydrogen towards the 2 carbons bond breaks between C and X

Question 41

what do the chlorine free radicals do

Answer 41

catalyses the decomposition ozone

Question 42

what are the products of the elimination reaction

Answer 42

water and the halogen

Question 43

what type of bond fission is present in halogenoalkanes

Answer 43

hetrolytic

Question 44

what must you not forrget on the ammonia

Answer 44

the lone pair

Question 45

what is thee geeneeral formula for ammonia

Answer 45

NH3

Question 46

what is meant by condition

Answer 46

either ethanolic or aqueous

Question 47

explain why the reactants are heated in a sealed container? (2 marks)

Answer 47

heated to increase ROR sealed tube to prevent loss of ammonia

Question 48

what is thee role of hydroxide ions in the elimination reaction

Answer 48

they act as a base

Question 49

Suggest why the reactions of halogenoalkanes with potassium cyanide is useful in industrial synthesis

Answer 49

it increases thee length of the carbon chain