Mechanisms

Question 1

What condition is required for free radical substitution?

Answer 1

UV light

Question 2

What is a free radical?

Answer 2

A reactive species with an unpaired electron

Question 3

What happens during free radical substitution?

Answer 3

In the presence of UV light a halogen substitutes for a hydrogen atom in an alkane/halogenoalkane to produce a halogenolakane and a hydrogen halide.

Question 4

What is heterolytic fission?

Answer 4

An endothermic process. Energy is added and the covalent bond breaks unevenly, both electrons going to the same atom

Question 5

What is homolytic fission?

Answer 5

An endothermic process. Energy is added and the covalent bond breaks evenly, one electron going to each atom producing free radicals.

Question 6

What are the steps in free radical substitution?

Answer 6

Initiation Propagation Termination

Question 7

Describe initiation in free radical substitution

Answer 7

A halogen molecule splits homolytically in the presence of UV light. Molecule produces a free radical.

Question 8

Describe propagation in free radical substitution

Answer 8

Molecule and a free radical react to produce a molecule and a free radical.

A) halogen free radical removes hydrogen from alkane.

B)Alkane free radical reacts with halogen

This is a chain reaction process.

Question 9

Describe termination in free radical substitution.

Answer 9

Free radicals react to form a molecule.

End of the reaction

Question 10

How can an excess of reactants be used to influence the products of free radical substitution?

Answer 10

Excess of alkane = one substitution

Excess of halogen = many substitutions.

Question 11

What is a nucleophile?

Answer 11

A lone pair donator.

Generally a negative ion or molecule with delta negative charge.

Question 12

What happens during nucleophilic substitution?

Answer 12

A nucleophlie replaces a halogen on a molecule.

Nucleophile is attracted to delta positive carbon caused by polar bond with an electronegative halogen.

Question 13

Give the possible nucleophiles in nucleophilic substitution.

Answer 13

:OH- hydroxide ion

:CN- cyanide ion

:NH3 ammonia

Question 14

Give the conditions for a hydroxide ion to act as a nucleophile in a nucleophilic substitution.

Answer 14

aqueous, warm, dilute

Question 15

Give the conditions for a cyanide ion to act as a nucleophile in nucleophilic substitution.

Answer 15

ethanolic, warm

Question 16

Give the conditions for ammonia to act as a nucleophile in nucleophilic substitution.

Answer 16

Excess concentrated ammonia dissolved in ethanol

(in a seeled container at constant pressure)

Question 17

Name the organic product for nucleophilic substitution with an hydroxide ion

Answer 17

Alcohol

eg methanol CH3OH

Question 18

Name the organic product for nucleophilic substitution with cyanide ions

Answer 18

Nitrile

e.g ethannitrile CH3CN

Question 19

Name the organic product of nucleophilic substitution with a ammonia nucleophile

Answer 19

amine

e.g ethylamine CH3CH2NH2

Question 20

Draw the mechanism for nucleophilic substitution with a hydroxide ion.

Answer 20

Question 21

Draw the mechanism for nucleophilic substitution with a cyanide ion nucleophile

Answer 21

Question 22

Draw the mechanism for nucleophilic substitution with an ammonia nucleophile.

Answer 22

Question 23

What a substitution reaction?

Answer 23

A reaction when an atom or group replaces another atom or group on the molecule

Question 24

what is an addition reaction?

Answer 24

A reaction where a group/atom is added to a unsaturated molecule to produce a saturated molecule.

Question 25

what is an electrophile?

Answer 25

A lone elctron pair acceptor Usually cations or delta positive

Question 26

What happens during an elimination reaction?

Answer 26

A hydrogen and halogen are removed from the saturated alkane to form an unstaurated alkene, water and a salt.

Question 27

What is a base?

Answer 27

A proton (H+) acceptor

Question 28

what is an acid?

Answer 28

A proton (H+) donor

Question 29

What is an alkali?

Answer 29

A soluble base. Produces OH- ions in water.

Question 30

What are the conditions for an elimaination reaction?

Answer 30

hot, ethanolic, concentrated potassium hydroxide

Question 31

What type of halogenoalkane favours elimination/nucleophilic substitution?

Answer 31

Primary favours nucleophilic substitution Tertiary favours elimination

Question 32

what does the hydroxide ion act as in a elimination reaction?

Answer 32

A base

Question 33

What hapens during electrohilic addition?

Answer 33

The carbon doudle bond opens and an atoms/groups are added to each carbon atom. This forms a saturated alkane from and unsaturated alkene.

Question 34

Name the intermediate of electrophilic addition

Answer 34

A carbocation

Question 35

What is the major/minor product?

Answer 35

Major - the product in highest abundance minor - the product in lowest abundance

Question 36

Why are alkenes suseptible to electrophilic addition?

Answer 36

The carbon-carbon double bond occurs in the overlap of two p orbitals. This creates an elctron rich π bond which attracts the positively charged electrophile.

Question 37

What is the positive inductile effect?

Answer 37

The ability of a alkyl group to repel electrons away from itself.

Question 38

How do you determin the major product from electrophilic addition?

Answer 38

The more stable carbocation will form the major product. The more stable carbocation will by have the reaction occuring at a carbon attached to more alkyl groups (increased positive inductile effect). These will push more electrons towards the carbocation

Question 39

Give the conditions for electrophilic addition with bromine

Answer 39

aqueous

Question 40

Give the conditions for electrophilic addition with sulfuric acid

Answer 40

Concentrated sulfuric acid (H2SO4), cold (room temperature)

Question 41

Give the product for electrophilic addition with sulphuric acid

Answer 41

an alkyl hydrogen sulphate

Question 42

What makes the product of electrophilic addition with sulphuric acid useful?

Answer 42

The product is an alkyl hydrogen sulphate. Adding water will give an alcohol (and sulphuric acid)

Question 43

Give the conditions for an elctrophilic addition reaction with hydrogen bromide

Answer 43

cold (room temperature)

Question 44

Give the reaction conditions for elctrophilic addition with water with a strong acid.

Answer 44

strong acid must be dissolved in the water.

Question 45

what is meant by a strong acid?

Answer 45

An acid that fully dissociates in water, gives a large amount of H+ ions in solution.

Question 46

what is interesting about electrophilic addition with water and a strong acid.

Answer 46

H+ ions from strong acid acid as electrophile Produces an intermediate carbocation. This reacts with the lone pair of an oxygen on a water molecule. A second intermediate is produced with a cation oxygen. This attracts the electrons in the oxygen hydrogen bond so hydrogen ions leave. Hydrogen ions act as a catalyst.

Question 47

draw the reaction mechanism for an elimination reaction

Answer 47

Question 48

draw the mechanism for a bromine electrophilic addition reaction

Answer 48

Question 49

draw the mechanism for an hydrogen bromide electrophilic addition reaction

Answer 49

Question 50

draw the mechanism for elctrophiic addition in water with a strong acid

Answer 50

Question 51

draw the reaction mechanism for electrophilic addition with sulphuric acid.

Answer 51

Question 52

Draw the structure of sulphuric acid

Answer 52

Question 53

Give all the possible electrophiles in electrophilic addition.

Answer 53

bromine (istantaneous dipole forms delta positive) Hydrogen brominde (hydrogen delta positive) Sulphuric acid (hydrogen delta positive) Water with strong acid (hydrogen ion)

Question 54

Name the organic product from an electrophilic addition reaction with sulphuric acid

Answer 54

alkyl hydrogen sulphate

Question 55

name the organic product from an electrophilic addition with water and a strong acid

Answer 55

an alcohol