Organic Chemistry 5 (mechanisms)

Question 1

Mechanism for Ionic addition

stage a

Answer 1

c=c bond in ethene is an area of negativity (4 electrons being shared) causes non-polar bromine to become polarised as it approaches the double bond, double bond repels electrons to bromine atom furthest away

Question 2

Mechanism for Ionic addition

stage b

Answer 2

polarisation causes bromine to spilt up into Br+ and Br- by heterolytic fission

Question 3

heterolytic fission

Answer 3

molecule splits to produce 2 different ions

Question 4

Mechanism for Ionic addition

stage c

Answer 4

Br+ attacks double bond to get 2 electrons it needs, dative covalent bond, double bond becomes single and other carbon has a positive charge (carbonium ion)

Question 5

Mechanism for Ionic addition

stage d

Answer 5

the positive carbonium ion is now attack by the Br - to form another dative covalent bond

Question 6

Mechanism for Ionic addition

how do you get the evidence

Answer 6

carry it out in the presence of sodium chloride solution

Question 7

Mechanism for Ionic addition

when carried out in sodium chloride solution, what proves the existence of the carbonium ion 1

Answer 7

trace amounts of 1-bromo-2-chloroethane formed when Cl- attacks the carbonium ion

Question 8

Mechanism for Ionic addition

when carried out in sodium chloride solution, what proves the existence of the carbonium ion 2

Answer 8

2-bromoethaol is formed when the water attacks the carbonium ion

Question 9

Mechanism for Ionic addition

with Cl2 instead of Br2

Answer 9

the Cl+ attacks the double bond first and then the Cl- attacks the carbonium ion to for 1,2-dichloroethane

Question 10

Mechanism for Ionic addition

with HCl instead of Br2

Answer 10

the H+ attacks the double bond first and then the Cl- attacks the carbonium ion to form chloroethane

Question 11

polymer

Answer 11

a very long chained molecule that is made when many thousands of small-chained molecules, called monomers, join together

Question 12

what is polythene used for 2

Answer 12

plastic bags, cling film

Question 13

what is polypropene used for

Answer 13

plastic jugs, beakers

Question 14

definition of a free radical substitution reaction

Answer 14

a free radical substitution reaction occurs when an atom or group of atoms are replaced by another group of atoms. there are two products

Question 15

free radical substitution reaction, monochlorination of methane
stage 1

Answer 15

initiation

Question 16

free radical substitution reaction, monochlorination of methane
stage 2

Answer 16

propagation

Question 17

free radical substitution reaction, monochlorination of methane
stage 3

Answer 17

termination

Question 18

free radical substitution reaction, monochlorination of methane
initiation stage

Answer 18

ultraviolet light causes chlorine to break down into Cl• and Cl• (homolytic fission)

Question 19

free radical substitution reaction, monochlorination of methane
why does it need UV light

Answer 19

it is a photochemical reaction

Question 20

free radical substitution reaction, monochlorination of methane
4 pieces of evidence

Answer 20

1. the reaction will not happen in the absence of u.v light
2. for every photon absorbed thousands of molecules of product are formed (chain reaction)
3. the formation of products such as ethane/chloroethane
4. radical promoters like tetramethyl lead speed up the reaction (existence of methyl radicals)

Question 21

free radical substitution reaction, monochlorination of methane stage 2 propagation, what does the Cl• do?

Answer 21

it attacks an unreactive methyl molecule to form HCl and a methyl radical

Question 22

free radical substitution reaction, monochlorination of methane stage 2 propagation is the methyl radical reactive

Answer 22

yes as it has an unpaired electron

Question 23

free radical substitution reaction, monochlorination of methane stage 2 propagation first equation

Answer 23

CH4 + Cl• -> CH3• + HCl

Question 24

free radical substitution reaction, monochlorination of methane stage 2, what does the methyl radical do

Answer 24

attacks a chlorine molecule to produce chloromethane and a reactive chlorine atom

Question 25

free radical substitution reaction, monochlorination of methane stage 2 why is the chlorine atom reactive

Answer 25

has an unpaired electron

Question 26

free radical substitution reaction, monochlorination of methane stage 2 propagation second equation

Answer 26

CH3• + Cl2 -> CH3Cl + Cl•

Question 27

free radical substitution reaction, monochlorination of methane stage 2 propagation
what does it mean that you produce another chlorine atom

Answer 27

a chain reaction ocurs

Question 28

free radical substitution reaction, monochlorination of methane stage 3 termination, 3 equations

Answer 28

Cl• + Cl• -> Cl2
CH3• + Cl• -> CH3Cl
CH3• + CH3• -> C2H6

Question 29

one promoter and formula

Answer 29

tetramethyl lead Pb(CH3)4

Question 30

free radical substitution reaction, monochlorination of ethane
does the initiation stage change?

Answer 30

no

Question 31

free radical substitution reaction, monochlorination of ethane main products

Answer 31

HCl and C2H5Cl

Question 32

free radical substitution reaction, monochlorination of ethane
3 termination equations

Answer 32

Cl• + Cl• -> Cl2
CH3• + C2H5• -> C2H5Cl
CH3• + CH3• -> C4H10

Question 33

C4H10

Answer 33

butane

Question 34

free radical substitution reaction, monochlorination of ethane
what does the product of butane prove

Answer 34

the existence of ethyl radicals

Question 35

free radical substitution reaction, monochlorination of ethane
one promoter

Answer 35

tetraethyl lead, Pb(C2H5)4