Colour by Design - Organic Mechanisms

Question 1

draw an example mechanism for electrophilic addition

Answer 1

Question 2

describe the process of electrophilic addition

Answer 2

a pair of electrons from the double bond attacks an electrophile to form a new bond

the other carbon in the double bond is now a carbocation

a nucleophile attacks the carbocation to form a bond

Question 3

what type of mechanism is alkenes reacting with bromine?

Answer 3

electrophilic addition

Question 4

what are the reaction conditions for the reaction between alkenes and bromine?

Answer 4

H in presence of a catalyst to form an alkane -> Ni + heat + pressure or Pt + RTP

water in presence of catalyst to give alcohol -> conc sulfuric then add steam

Question 5

draw an example mechanism for nucleophilic substitution

Answer 5

Question 6

what is a nucleophile?

Answer 6

a molecule with a lone pair of electrons that it can donate to form a dative covalent bond

Question 7

describe the process of nucleophilic substitution

Answer 7

nucleophile attacks carbon deficient atom in C-X bond

nucleophile donates 2 electrons to form dative covalent bond

C-X bond breaks heterolytically and X recieves 2 electrons, leaving compound as X^-

Question 8

describe heterolytic bond breaking

Answer 8

both electrons from bond goes to one atom

one positive and one negative ion produced

Question 9

describe homolytic bond breaking

Answer 9

each atom gets 1 electron from bond breaking

2 radicals produced

Question 10

what is a radical?

Answer 10

a species with an unpaired electron

Question 11

what are the 3 steps in radical reactions?

Answer 11

initiation

propogation

termination

Question 12

what happens during the initiation step in a radical reaction?

Answer 12

one or more molecules react to form radicals

a bond breaks by homolytic fission

often in presence of UV light

Question 13

what happens during the propogation steps of radical reactions?

Answer 13

molecule and radical react to form new molecule or radical pair

bond breaks and new bond forms

usually occurs in pairs - one step produces intermediate that then reacts in second step

Question 14

what happens during termination steps in radical reactions?

Answer 14

2 radicals react to form one molecule

bonds form so exothermic

Question 15

what is the functional group of a cyano compound?

Answer 15

N≡C^-

Question 16

what can cyano groups also be known as?

Answer 16

nitrile groups

Question 17

are nitriles electophilic or nucleophilic?

Answer 17

nucleophilic

Question 18

draw an example mechanism of nucleophilic addition

Answer 18

Question 19

where does the hydrogen ion come from in nucleophilic addition?

Answer 19

acidic conditions

Question 20

what are the products of nucleophilic addition involving cyano groups called?

Answer 20

cyanohydrins

Question 21

what are cyanohydrins?

Answer 21

a molecule with a cyano group and hydroxy group on the same carbon

Question 22

what happens when haloalkanes react with HCN?

Answer 22

halogen acts similar to O in nucleophilic addition

if halogen is a good leaving group - nucleophilic substitution, if not - nucleophilic addition

Question 23

why won’t benzene undergo electrophilic addition?

Answer 23

in order to go through mechanism - delocalisation would have to be broken as double bonds aren’t fixed around molecule

Question 24

draw a general mechanism for the electrophilic substitution of arenes

Answer 24

Question 25

why are catalysts often used in the electrophilic substitution of arenes?

Answer 25

initial attack of the electrophile is often slow and energetically unfavourable

Question 26

what catalysts are usually used for the electrophilic substitution of arenes?

Answer 26

iron filings or iron(III) bromide for bromination

aluminum chloride for chlorination

conc sulfuric acid for nitration

anhydrous aluminum chloride for alkylation and acylation

Question 27

what is the role of the catalyst in the bromination of arenes?

Answer 27

to form the Br⁺ ion

Question 28

what is the role of the catalyst in the chlorination of arenes?

Answer 28

to form the Cl⁺ ion

Question 29

what are the reaction conditions for the electophilic substitution of arenes with bromine?

Answer 29

heat under reflux

FeBr₃ catalyst

Question 30

what are the reaction conditions for the electrophilic substitution of arenes with chlorine?

Answer 30

aluminum chloride catalyst

Question 31

draw the equation for the nitration of benzene in electrophilic substitution

Answer 31

Question 32

why must the temperature stay below 55ºC during the nitration of arenes?

Answer 32

if higher - explosives formed (dinitro- and trinitro-)

Question 33

what are the reaction conditions for the nitration of arenes?

Answer 33

conc sulfuric

under 55 degrees c

Question 34

draw the equation for the sulfonation of arenes

Answer 34

Question 35

what are the reaction conditions for the sulfonation of arenes?

Answer 35

reflux

acid reactant must be very concentrated

Question 36

what is alkylation?

Answer 36

adding an alkyl group to something

Question 37

draw an equation for the alkylation of arenes

Answer 37

Question 38

what are the reaction conditions for the alkylation of arenes?

Answer 38

anhydrous aluminum chloride, heat under reflux

Question 39

draw an equation for the acylation of arenes

Answer 39

Question 40

what are the reaction conditions for the acylation of arenes?

Answer 40

anhydrous aluminum chloride, heat under reflux

Question 41

why is the acylation/alkylation of arenes important?

Answer 41

important in synthesis as a way of forming C-C bonds and forming side-chains.