Organic Chemistry

Question 1

what is optical isomerism?

Answer 1

• same structural formula, different arrangement of atoms in space
• mirror images of each other
• have chiral carbon atom

Question 2

what is a chiral carbon?

Answer 2

has 4 different groups attached

Question 3

what are enantiomers?

Answer 3

molecules that are mirror images of each other and are non-superimposable

Question 4

how can you tell if isomers are optically active?

Answer 4

will rotate plane polarised light

Question 5

what is a racemic mixture?

Answer 5

mixture with equal amounts of each enantiomer

Question 6

why don’t racemates rotate plane polarised light?

Answer 6

2 enantiomers rotate light in opposite directions + they cancel out

Question 7

what are aldehydes oxidised to?

Answer 7

carboxylic acids

Question 8

outline how tollens reagent is made

Answer 8

add a few drops of NaOH and a few drops of dilute NH₃ to silver nitrate until the pale brown ppt dissloves

Question 9

what can tollens reagent be used for? how?

Answer 9

• testing for aldehydes and ketones
• aldehydes: tollens reduced to silver mirror
• ketones: no ppt formed

Question 10

what can Fehling’s solution be used for? how?

Answer 10

• test for aldehydes and ketones
• add warm to aldehyde/ketone
• aldehyde will turn blue solution to red red ppt (Cu₂)
• ketone solution remain blue

Question 11

name one reducing agent used to reduce aldehydes/ketones? what is formed?

Answer 11

• NaBH₄
• primary (aldehydes) or secondary alcohols (ketones)

Question 12

what is esterification?

Answer 12

formation of esters by reacting alcohols with carboxylic acids or acid anhydrides

Question 13

give a word equation for the production of an ester from an alcohol and carboxylic acid. include the name of the catalyst

Answer 13

carboxylic acid + alcohol –sulfuric acid–> ester + water

Question 14

give a word equation for the production of an ester from an alcohol and acid anhydride

Answer 14

acid anhydride + alcohol —-> ester + carboxylic acid

Question 15

give an example of an ester. which alcohol and carboxylic acid is required to make this?

Answer 15

methyl ethanoate
methanol + ethanoic acid

Question 16

what are the uses of esters?

Answer 16

• perfumes + food flavourings
• solvents -> polar so compounds will dissolve readily in esters
• glues -> low bp + evaporate easily
• plasticisers

Question 17

what are the conditions required for the acid hydrolysis of esters? what is produced?

Answer 17

• dilute acid (sulfuric/HCl)
• reflux
• carboxylic acid + alcohol

Question 18

what are the conditions required for the base hydrolysis of esters? what is produced?

Answer 18

• dilute base, e.g. NaOH
• reflux
• carboxylate ion + alcohol

Question 19

what is the IUPAC name for glycerol?

Answer 19

propane-1,2,3-triol

Question 20

give an example of a fat or oil with unsaturate hydrocarbon chains?

Answer 20

vegetable oils

Question 21

what are the properties of oils/fats with unsaturated hydrocarbon chains? why?

Answer 21

• liquids at room temp
• chains not straight = can’t pack closely together = weaker vdw = lower mp

Question 22

give an example of an oil/fat with saturated hydrocarbon chains

Answer 22

animal fats

Question 23

what are the properties of oils/fats with saturated hydrocarbon chains?

Answer 23

• solids at room temp
• staight + more uniform chains = can pack closely together = stronger vdw = higher mp

Question 24

how can soap be produced? give a word equation.

Answer 24

hydrolysing animal fats and vegetable oils by heating with NaOH
fat + sodium hydroxide –> glycerol + soap (sodium salt)

Question 25

what is biodiesel? how can it be produced? give a word equation.

Answer 25

- mixture of fatty acids made from methyl esters + can be made from rapeseed oil - reacting vegetable oils with methanol with a potassium hydroxide catalyst oil + methanol --> glycerol + methyl ester

Question 26

what is the functional group of acyl chlorides?

Answer 26

-COCl

Question 27

give an example of an acyl chloride

Answer 27

ethanoyl chloride CH₃-C_\Cl=O

Question 28

what does the reaction of acyl chlorides with water produce? give a word equation for the reaction of ethanoyl chloride and water.

Answer 28

ethanoyl chloride + water --> ethanoic acid + HCl

Question 29

what does the reaction of acyl chlorides with ammonia produce? give a word equation for the reaction of ethanoyl chloride and ammonia.

Answer 29

amides ethanoyl chloride + ammonia --> ethanamide + HCl

Question 30

what does the reaction of acyl chlorides with alcohol produce? give a word equation for the reaction of ethanoyl chloride and methanol.

Answer 30

esters ethanoyl chloride + methanol --> methyl ethanoate + HCl

Question 31

what does the reaction of acyl chlorides with primary amines produce? give a word equation for the reaction of ethanoyl chloride and methylamine.

Answer 31

ethanoyl chloride + methylamine --> N-methylethanamide + HCl

Question 32

what is an acid anhydride?

Answer 32

molecule made from 2 carboxylic acids that are the same

Question 33

give an example of an acid anhydride

Answer 33

ethanoic anhydride

Question 34

which reactions are more vigorous, acyl chloride reactions or acid anhydride reactions

Answer 34

acyl chloride reactions

Question 35

what does the reaction of acid anhydrides with water produce? give a word equation for the reaction of ethanoic anhydride and water.

Answer 35

carboxylic acids ethanoic anhydride + water --> ethanoic acid + ethanoic acid

Question 36

what does the reaction of acid anhydrides with ammonia produce? give a word equation for the reaction of ethanoic anhydride and ammonia.

Answer 36

amides ethanoic anhydride + ammonia --> ethanamide + ethanoic acid

Question 37

what does the reaction of acid anhydrides with alcohol produce? give a word equation for the reaction of ethanoic anhydride and methanol.

Answer 37

esters ethanoic anhydride + methanol --> methyl ethanoate + ethanoic acid

Question 38

what does the reaction of acid anhydrides with primary amines produce? give a word equation for the reaction of ethanoic anhydride and methylamine.

Answer 38

N-substituted amides ethanoic anhydride + methylamine --> N-methylethanamide + ethanoic acid

Question 39

by what mechanism do acyl chlorides react?

Answer 39

nucleophilic addition elimination

Question 40

why are acyl chlorides susceptible to attack from nucleophiles?

Answer 40

have a strong partial negative on the carbon, as oxygen/chlorine atoms are electronegative

Question 41

outline nucleophilic addition elimination

Answer 41

- nucleophile attacks partially pos carbon - e move from double bond to oxygen - e move from oxygen to the bond - e move from bond to chlorine - e move from detached chlorine to a hydrogen

Question 42

what is aspirin? how is it made?

Answer 42

ester made by reacting ethanoic anhydride or ethanoyl chloride + salicylic acid

Question 43

why is ethanoic anhydride is used instead of ethanoyl chloride in industry?

Answer 43

- safer as less corrosive, doesnt produce harmful HCl gas and doesnt react vigorously with water - cheaper

Question 44

describe the structure of benzene

Answer 44

- cyclic, planar molecule - each carbon is bonded to 2 other carbons and 1 hydrogen atom - e form delocalised e ring - all C-C bond same length

Question 45

why is benzene more stable than the theoretical alternative cyclohexa-1,3,5-triene?

Answer 45

- measure stability by comparing enthalpy change of hydrogenation in both - if cyclohexene hydrogenated has enthalpy change of -120 so benzene expected to have -360 due to 3 double bonds but actually has -208 - suggests more energy is required to break bonds = more stable due to delocalised e structure

Question 46

what are aromatic compounds/arenes?

Answer 46

molecules that contain a benzene ring

Question 47

what kind of reactions do aromatic compounds/arenes undedrgo?

Answer 47

electrophilic substitution

Question 48

why does benzene not undergo electrophilic addition reactions?

Answer 48

stable

Question 49

list 2 types of electrophilic substitution

Answer 49

- friedel crafts acylation - nitration

Question 50

what is friedel crafts acylation?

Answer 50

acyl chloride and halogen carrier (AlCl₃) react to create a strongly positive electrophile

Question 51

why is friedel crafts acylation necessary?

Answer 51

- stability makes benzene harder to react - adding acyl group makes benzene molecule weaker

Question 52

give an equation for friedel crafts acylation

Answer 52

RCOCl + AlCl₃ --> RC⁺=O + AlCl₄^-

Question 53

outline the mechanism for friedel crafts acylation (what to draw)

Answer 53

1. arrow from circle in benzene ring to RC⁺=O 2. arrow from AlCl₄^- to RC⁺=O 3. R-C-benzene ring with =O on c + HCl + AlCl₃

Question 54

what is nitration of benzene used for?

Answer 54

making dyes and explosives

Question 55

what conditions are required for the nitration of benzene?

Answer 55

- conc nitric acid - conc sulfuric acid - 50c

Question 56

give 2 equations for the reactions that take place before the nitration of benzene

Answer 56

1. HNO₃ + H₂SO₄ --> H₂NO₃⁺ + HSO₄^- 2. H₂NO₃⁺ --> NO₂⁺ + H₂O

Question 57

outline the mechanism for the nitration of benzene (what to draw)

Answer 57

1. arrow from circle in benzene e ring to +NO₂ 2. NO₂ attached to benzene, arrow from H on benzene to half benzene e ring with + in middle 3 NO₂ attached to benzene + H⁺ (to react with HSO₄^- to regenerate catalyst)

Question 58

how does temperature affect the nitration of benzene?

Answer 58

- temp below 55c will ensure a single NO₂ - above will result in multiple substitutions

Question 59

what kind of molecule is phenylamine?

Answer 59

aromatic primary amine