Halogenoalkanes

Question 1

What happened when alkanes react with uv-light?

Answer 1

they form halogenoalkanes and hydrogen halides

Question 2

What is the equation fir the reaction with alkanes in uv-light

Answer 2

halogen + alkane > halogenoalkane + hydrogen halide

Question 3

what is a free radical?

Answer 3

reactive species due to the pre of an unpaired electron

Question 4

what happened in the initiation step?

Answer 4

uv light causes a covalent bond between halogens atoms to break and this creates 2 halogen radicals

X2 > 2X•

Question 5

What happens in the first propagation step?

Answer 5

The halogen radical reacts with an alkane
radical removes a hydrogen from the alkane creating a hydrogen halide molecule

CH4 + X• > •CH3 + XH

alkane is left as a alkyl radical

Question 6

What happens in the second propagation step?

Answer 6

alkyl radical reacts with a halogen molecule and created a halogenoalkane
remaining halogen is left as a halogen radical

•CH3 + X2 > •X + CH3X

Question 7

What happens in the termination step?

Answer 7

2 radicals will react to form a molecule
either:

two halogen radicals
halogen radical + alkyl radical
two alkyl radicals

Question 8

what are short chain chlorofluorocarbons used for?

Answer 8

they are gases and were used fir refrigerators

Question 9

what are long chain chlorofluorocarbons used for?

Answer 9

dry cleaning and de-greasing solvents

Question 10

what happened when chlorofluorocarbons are decomposed?

Answer 10

they form chlorine free radicals when in the atmosphere

Question 11

why is the ozone layer important?

Answer 11

absorbs harmful uv radiation

Question 12

how is a chlorine radical formed?

Answer 12

C-Cl breaks in the presence of uv radiation to form Cl•

R-Cl > R• + Cl•

Question 13

What is the equation for the decomposition of ozone?

Answer 13

Cl• + O3 > ClO• + O2

Question 14

What is the equation for ClO• attacking more radicals?

Answer 14

ClO• + O3 > 2O2 + Cl•

Question 15

What is the overall equation to show ozone breakdown?

Answer 15

2O3 > 3O2

Question 16

What is a primary halogenoalkane?

Answer 16

halogen is bonded to a C that is bonded to 1 other C

Question 17

What is a secondary halogenoalkane?

Answer 17

halogen is bonded to a C that is bonded to 2 other Cs

Question 18

What is a Teritary halogenoalkane?

Answer 18

halogen is bonded to a C that is bonded to 3 other Cs

Question 19

What is a mechanism?

Answer 19

pictorial representation of the movement of a pair of electrons during a chemical reaction

Question 20

What is a nucleophile?

Answer 20

donate electron pairs to electrophiles

Question 21

What happens in nucleophilic substitution?

Answer 21

• nucleophile donates lone pair to carbon and forma a covalent bond
• carbon gives electrons back to halogen and bond breaks

Question 22

What are the conditions for nucleophilic substitution?

Answer 22

warm aqueous solution

Question 23

What are the conditions for nucleophilic substitution to form amines?

Answer 23

warmed in excess of ammonia

Question 24

What is the overall equation for nucleophilic substitution to form amines?

Answer 24

CH3CH2X + 2NH3 > CH3CH2NH2 + NH4X

Question 25

what is formed when a primary amine recast with another halogenoalkane

Answer 25

secondary amine

Question 26

what forms when a secondary amine reacts with another halogenoalkane?

Answer 26

tertiary amine

Question 27

what happened when a tertiary amine reacts with another halogenoalkane?

Answer 27

quaternary ammonium salt

Question 28

What are the conditions for elimination?

Answer 28

hot ethanol

Question 29

What is formed after elemination

Answer 29

an alkene and water

Question 30

What are the steps of elimination?

Answer 30

• hydroxide removes a hydrogen from an adjacent carbon to the halogen
• electrons in C-H move to the C-C bond to create a double bond
• electrons in C-Halogen move into halogen breaking the bond and forming a halide ion