Organic Chemistry Flashcards
1
Q
Optical Isomers/Enantiomers
A
Pairs of molecules that are non-superimposable mirror images of each other
2
Q
Chiral
A
Asymmetric structure such that mirror images are non-superimposable
3
Q
Condition for a molecule to be chiral
A
Must have four different substituent groups attached to chiral carbon
4
Q
Racemate
A
50:50 mixture of two enantiomers
5
Q
Measuring Optical Activity
A
- polarimeter
- polarised light passed through solution containing enantiomers
- rotate plane of polarisation in OPPOSITE directions
6
Q
Compare enantiomers of a molecule
A
- same physical/chemical properties (except for with other chiral molecules)
- rotate plane of polarisation in OPPOSITE directions
- different reaction with other enantiomers
7
Q
Physical Properties of Carbonyl Compounds
A
- high boiling point due to dipole-dipole forces
- soluble since hydrogen bonds form between lone pair on oxygen and water
- very reactive due to C=O bond which is attacked by nucleophiles
8
Q
Explain why nucleophilic addition of carbonyl molecules with KCN produces a racemic mixture
A
- carbonyl molecule is planar
- :CN has equal chance of attacking
- C=O from above or below the plane
9
Q
Fehling’s Test
A
- distinguish between aldehyde and ketone
- Fehling’s A = blue solution of copper (II) ions
- Fehling’s B = alkali and complexing agent
- brick red precipitate of copper (I) oxide
10
Q
Tollen’s Reagent
A
- distinguish between aldehyde and ketone
- [Ag(NH3)2]+
- silver mirror forms
11
Q
Reduction of aldehydes and ketones
A
- nucleophilic addition using hydride :H- ion written 2[H]
- NaBH4 sodium tetrahydridoborate / methanol or water
- LiAlH4 lithium tetrahydridoaluminate / ether or dry
Aldehyde => primary alcohol
Ketone => secondary alcohol
Carboxylic Acids => primary alcohol (only using LiAlH4)
12
Q
Suggest why NaBH4 does not react with carboxylic acids
A
Not strong enough to reduce carboxylic acids
13
Q
Delocalisation of carboxylate ion
A
- resonance
- negative charge (e-) delocalised between two electronegative oxygen atoms
- more stable
14
Q
Methods of producing esters
A
- carboxylic acid + alcohol (strong acid catalyst) by esterification
- acyl chloride + alcohol by acylation
- acid anhydride + alcohol by acylation
15
Q
Naming Esters
A
Number carbons from -O- bond
Alcohol name then Acid/Acyl name
16
Q
Methods of hydrolysis of esters
A
aqueous ester with
- acid catalyst
- base catalyst
17
Q
Compare hydrolysis of esters using acid and base catalysts
A
acid catalyst
- reforms equilibrium mixture of acid and alcohol
base catalyst
- reacts with carboxylic acid forming salt of acid
- reaction goes to completion so equilibrium not established
18
Q
IUPAC name of glycerol
A
Propane-1,2,3-triol
19
Q
Common uses of esters
A
- solvents
- plasticisers
- perfumes
- food flavourings
20
Q
Explain why sodium salts produced from hydrolysis of esters can be used in soaps
A
- sodium salts are ionic and can dissociate to form Na+ and carboxylate ion
- carbon chain is non polar so mixes with grease
- carboxylate ion is polar so mixes with water
21
Q
Biodiesel
A
- mixture of methyl esters of long chain carboxylic acids
Triglyceride (Vegetable Oil) + 3 Methanol (NaOH catalyst) -> Fatty Methyl Esters + Glycerol
22
Q
Acylation
A
Process by which acyl group ( R-C=O) is introduced into another molecule
23
Q
Carboxylic Acid Derivatives
A
Compounds that can be converted to carboxylic acids via acidic/basic hydrolysis (acyl group + Z group)
24
Q
Examples of Acid Derivatives
A
- ester
- acyl chloride
- acid anhydride
25
Order of reactivity for addition-elimination reactions with any chlorides and acid anhydrides
Primary amine ( = N substituted amine)
Ammonia ( = Amide)
Alcohol ( = Ester)
Water ( = Carboxylic acid)
26
Advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of aspirin
- cheaper
- forms ethanoic acid rather than hydrogen chloride
- safer / less corrosive
27
Order of boiling points for functional groups with similar Mr
Carboxylic Acids - hydrogen bonding dimerise
Alcohols - hydrogen bonding (+ primary have larger surface area so more contact points therefore more van der Waals)
Ketones - stronger dipole-dipole due to two electron donating alkyl groups around C=O group
Aldehydes - dipole-dipole
Alkanes - only van der Waals
28
Flaws in Kekulé model of benzene
- should undergo electrophilic addition but rarely does
- reaction with bromine should give rise to three isomers but only one produced
- hexagon should not be symmetrical but x-ray diffraction shows it is a perfect hexagon
- thermochemical data for hydrogenation implies lower in energy so more stable than thought (shows reaction is less exothermic than predicated based on cyclohexene)
29
Suggest how to differentiate benzene from cyclohexene
Bromine water - benzene does not decolourise since it rarely undergoes electrophilic addition
30
Explain the stability of benzene
- resonance (lower energy state)
| - delocalised electrons in p orbitals above and below the plane of the aromatic ring
31
Suggest why benzene has a higher boiling point than hexane
- flat structure rather than puckered
| - molecules can pack closer together so stronger vdw
32
Suggest why reactions with benzene are most likely to be electrophilic substitutions
- delocalised e- prone to attack by electrophiles
| - aromatic ring is very stable so often remains in tact
33
Suggest why a smoky flame is an indication of an aromatic compound
Benzene ring has a high carbon:hydrogen ratio
34
Conditions for nitration of benzene
- concentrated sulphuric acid
- concentrated nitric acid
- 20-60 degrees C
35
Suggest how reaction between sulphuric acid and nitric acid creates nitronium electrophile
H2SO4 + HNO3 -> NO2+ + H2O + HSO4-
- sulphuric acid is stronger acid so donates H+ to nitric acid
- sulphuric acid is catalyst
36
Describe what would happen if nitration of benzene occurred above 55 degrees C
Multiple points of substitution (nitration)
37
Suggest uses of nitrated arenes
- explosives (TNT)
- industrial dyes
- formation of amines
38
Describe structure of benzene
- planar
- stable due to delocalised system in aromatic ring
- bond length intermediate between C-C and C=C
39
Conditions for Friedel-Crafts Acylation
- AlCl3 / FeCl3 catalyst
- aycl chloride
CH3COCl + AlCl3 -> AlCl4- + CH3CO+
40
Suggest why ammonia is a better nucleophile than water
Nitrogen is less electronegative than oxygen so donates lone pair of electrons more readily
41
Suggest why a primary amine is a better nucleophile than ammonia
Primary amine has electron-donating alkyl groups attached to nitrogen so donates lone electron pair more readily due to positive inductive effect
42
Suggest why geometrical isomers are formed from dehydration of alcohols
Loss of H+ from end of C next to C-OH
43
Conditions for esterfication
- strong acid, e.g. sulfuric acid
- warm (<100 degrees C)
- reflux
44
Conditions for acylation with acyl chloride
- (alcohol reagent)
- no acid
- room temperature (since acyl chloride highly reactive)
45
Conditions for acylation with acid anhydride
- (alcohol reagent)
- no acid
- heat/reflux
46
Suggest why a tertiary alcohol cannot be oxidised
No H attached to same carbon as -OH group/ x3 alkyl groups attached to C-OH
47
State mechanism for esterification
Addition-Elimination
48
Test to differentiate between ethanoyl chloride and chloroethane
Silver Nitrate
Ethanoyl Chloride - white precipitate
Chloroethane - no reaction
49
Explain why amines have lower boiling points than alcohols
- hydrogen bonding is not as strong as in alcohols
| - nitrogen is less electronegative than oxygen
50
Explain why phenylamine is not very soluble
- benzene ring cannot form hydrogen bonds
51
Suggest why amines are often supplied as hydrochlorides in medication
- insoluble amine converted to soluble hydrochloride salt
| - more soluble in bloodstream
52
Suggest how amines can be identified
- strong fishy smell
53
Suggest why secondary/tertiary amines are relatively insoluble in water and describe how to covert them into soluble amine salts then back to amines
- long hydrophobic carbon tails cannot form H bonds with water
- add HCl to form hydrochloride which contains ions that dissolve in water
- add strong base like NaOH to regenerate insoluble amine
54
Suggest why tertiary amines are weaker bases than primary and secondary amines
lone pair on N is inaccessible to H+
55
Suggest why phenylamines are the weakest bases
- lone pair on N
- delocalised into aromatic ring
- least able to donate electron pair
56
Suggest difference in major product formed when ammonia is in excess compared to halogenoalkane, and vice versa
ammonia in excess => primary amine
| halogenoalkane in excess => quaternary ammonium salt
57
Suggest two methods of producing a primary amine from a halogenoalkane
- KCN/aq+ethanol => nitrile
- 2H2 or 4[H] / Ni catalyst => primary amine
OR
- EXCESS NH3 => primary amine
58
Suggest why reduction of nitriles is preferred to nucleophilic substitution with halogenoalkanes in manufacture of primary amines
- purer product since only primary amine can be formed
| - several nucleophilic substitutions can occur
59
Suggest how phenylamine can be formed from nitrobenzene
- reduction
- Sn/HCl
- room temperature
- tin and hydrochloric acid react to form H2 which reduces NO2 to 2H20
- 6[H] required
60
Suggest how N substituted phenyl amine can be formed from phenylamine
- nucleophilic substitution
| - halogenoalkane
61
Common uses of amines
- manufacture of nylon, polyurethane, dyes and drugs
| - synthesis of quaternary ammonium compounds to act as cationic surfactants in hair and fabric conditioners
62
Describe how cationic surfactants work
- ions cluster with charged ends in water
- hydrocarbon tail on surface
- form a coating preventing build up of static charge
63
Suggest why secondary amines have a lower boiling point than primary amines
- form hydrogen bonds
| - nitrogen atom in the middle of the chain rather than at the end so have a weaker dipole
64
Suggest why tertiary amines have a lower boiling point compared to primary and secondary
- no H attached to N so no hydrogen bonding
| - only dipole-dipole
65
Suggest why LiAlH4 is used rather than NaBH4 to reduce nitriles to primary amines
- NaBH4 is not a strong enough reducing agent
66
Suggest combinations of molecules which can join to make condensation polymers
- dicarboxylic acids and diols (=polyesters)
- dicarboxylic acids and diamines (=polyamides)
- amino acids
67
Suggest what is meant by a condensation reaction
reaction in which two molecules combine to form a larger molecule while eliminating a small molecule, e.g. water
68
Describe the structure of cisplatin
- Pt(NH3)2Cl2
| - square planar
69
Explain how cisplatin works as an anti-cancer drug
- bonds to nitrogen atom (lone N on smaller ring) on two adjacent guanine bases on DNA strand
- by ligand substitution reaction
- lone pairs on nitrogen form dative covalent bond with Pt
- Cl- displaced
- prevents transcription of DNA
- DNA replication cannot occur
- cells cannot replicate so die
70
Suggest why transplatin would be ineffective as an anti-cancer drug
- Cl- are not on the same side of Pt
- only one Cl- displaced by lone pair of nitrogen on guanine
- one bond is weak / could easily break
- not effective is stopping transcription of DNA
71
Suggest possible side effects of using cisplatin and how these could be minimised
- death of healthy cells that replicate rapidly, e.g. hair cells
- small doses
- targeted treatment
72
Uses of condensation polymers
- clothing, carpets and rugs from nylon 6,6
- fire-resistant clothing from terylene
- bullet proof vests from kevlar
73
Compare properties of addition polymers with condensation polymers
- AP have more branching due to random free radical addition mechanism
- CP have long, straight chains so have a higher tensile strength
- CP have hydrogen bonds between chains so can form helical structures
- CP are biodegradable due to C=O POLAR bonds which are readily attacked by nucleophiles (hydrolysed)
- AP are non-biodegradable due to long non-polar chains AND strong C-C bonds
74
Suggests methods of disposing of polymers
- landfill sites
- incinerate (release green house gases and toxic fumes)
- recycling
75
Evaluate recycling as a method of disposal for polymers
Advantages
- saves raw materials
- reduces landfill
- lower cost for recycling than making from raw materials
- reduces CO2 emission by not being incinerated
Disadvantages
- difficult and costly to sort and collect
- easily contaminated/not always suitable for purpose
- (limited number of times to recycle before polymer chains degrade)
76
Suggest what determines if an amino acid is alpha or beta
number of carbon atoms between amino and carboxylic acid group
77
Explain what is meant by a zwitterion and why this means all amino acids are solid at room temperature
- double ion which has separate positive and negatively charged groups
- formed when H+ from carboxylic acid group on amino acid is transferred to amine group
- amino acids exits as zwitterions so have ionic bonding between them so form solids at room temperature
78
Define isoelectric point
pH at which zwitterion exists
79
Describe what happens to amino acids at high and low pHs
- deprotonated at high pH
- protonated at low pH
- zwitterion only forms at isoelectric point so amino acid is either acidic or basic
80
Geometrical Isomerism
- or E/Z isomerism
- type of stereoisomerism
- refers to positions of substituents at either side of carbon-carbon double bond
81
Suggest advantages and disadvantages of producing esters with acyl chlorides rather than carboxylic acids
Advantages
- greater yield/reaction goes to completion (irreversible)
- faster
Disadvantages
- dangerous/ vigorous (exothermic)
- HCl produced rather than water which is toxic
- acyl chlorides are more expensive
82
State by products formed when producing esters from
a) carboxylic acids
b) acyl chlorides
c) acid anhydrides
a) water
b) hydrogen chloride
c) carboxylic acid based in acid anhydride
83
Give the structural formula of the first three acid anhydrides
methanoic anhydride - (HCO)2O
ethanoic anhydride - (CH3CO)2O
propanoic anhydride - (CH3CH2CO)2O
84
Explain why melting point of aminoethanoic acid is higher than hydroxyethanoic acid
- ionic bonding in aminoethanoic acid due to presence of zwitterions
- bonding in aminoethanoic acid is stronger than in hydroxyethanoic acid
85
Give the structure of the amide functional group and describe how to name a N-substituted amide
```
N-C=O
1) N-(alkyl group)
2) name carbon chain and remove "e" from end
3) -amide suffix
e.g. CH3-CONH-CH2CH2CH3
N-propylethanamide
```
86
Suggest disadvantages of producing primary amines by nucleophilic addition with KCN followed by hydrogenation
- KCN is toxic/poisonous
| - lower yield since two step process
87
Give reagents and conditions to produce hydroxynitriles from carbonyl molecules
- KCN
| - aqueous AND ethanolic
88
Explain why bromobenzene does not react with ammonia to produce phenylamine
- benzene ring only attacked by electrophiles
- ammonia is a nucleophile
- benzene repels nucleophiles (so nucleophilic substitution cannot occur)
89
Compare different secondary structures of proteins
- alpha helix : polypeptide forms hydrogen bonds with itself
- beta pleated sheet : hydrogen bonds form between adjacent polypeptides
90
Explain how ionic bonds and disulphide bridges form in tertiary structure of protein
- ionic bonds between -NH3+ and -COO-
| - disulphide bridges between S on different R groups in presence of oxygen (eliminate water)
