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Organic Chemistry Flashcards

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1
Q

When does optical isomerism occur

A
  • substances that have the same molecular + structural formula but cannot be superimposed on each other
  • occurs in molecules which contain a chiral centre
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2
Q

What is an enantiomer

A
  • non-super impossible mirror image molecules
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3
Q

Describe the properties of optical isomers?

A
  • same physical properties
  • same chemical properties
  • different biological activity
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4
Q

What is biological activity

A
  • the way they interact with other optically active molecules, receptors or active sites
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5
Q

Why are non-superimposable mirror image molecules called optical isomers?

A
  • they differ in the way they rotate the plane of plane polarised light
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6
Q

What is plane polarised light?

A
  • light that has been passed through a Polaroid
  • only oscillates in one plane
  • when passed through solutions of different optical isomers, the plane will be rotated by an equal angle but in opposite directions
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7
Q

Is rotation of plane polarised light clockwise + or -

A

+

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8
Q

What happens if the sample contains equal amounts of both enantiomer

A
  • it will be optically inactive
  • no effect on plane polarised light
  • RACEMIC MIXTURE
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9
Q

What is plane polarised light

A

Waves having vibration in the same direction for all waves

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10
Q

What does optically active mean

A
  • capable of rotating the plane of vibration of polarised light left or right
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11
Q

What is a racemic mixture

A
  • mixture of equal quantities of enantiomer
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12
Q

What sort of compounds undergo nucleophilic addition reactions?

A
  • aldehydes
  • ketones
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13
Q

What is a nucleophile?

A
  • electron pair donor
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14
Q

What is addition?

A
  • the addition of a molecule across a double bond (breaks it, gives one product)
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15
Q

What are the two types of reaction which occur via nucleophilic addition?

A
  • reduction of aldehydes/ketones
  • addition of HCN to an aldehyde/ketone (to form hydroxynitriles)
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16
Q

State the conditions for a reduction reaction through nucleophilic addition

A

Reagent: NaBH4
Nucleophile: :H- (hydride ion)
Conditions: Aqueous

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17
Q

State the conditions for an addition reaction via nucleophilic addition

A

Reagent: KCN
Nucleophile: :CN- (cyanide ion)
Conditions: dilute acid (HCl)

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18
Q

Outline the mechanism for nucleophilic addition

A
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19
Q

Where does the H+ in the mechanism come from?

A

I) when NaBH4 is used - H+ comes from the aqueous solvent (H2O)
II) when KCN in dilute acid is used - H+ comes from the dilute acid solvent

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20
Q

What is reduction?

A
  • loss of bonds to oxygen (or the gain of hydrogen)
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21
Q

How do u form tertiary alcohols

A

Reduction of aldehydes

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22
Q

How do u form secondary alcohols

A

Reduction of ketones

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23
Q

Can tertiary alcohols be formed from the reduction of an aldehyde or ketone?

A

NO

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24
Q

Why do we use HCN instead of KCN?

A
  • because KCN only supplies :CN-
  • H+ comes from acid
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25
Q

Why is addition of HCN a useful reaction?

A
  • useful in synthesis
  • increases length of carbon chain
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26
Q

Why is 2-hydroxypropane nitrile formed as a racemic mixture?

A
  • the carbonyl group is planar so attack by the :CN- ion is equally likely from either side
  • enantiomer are formed in equal amount
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27
Q

What is the general formula for carboxylic acids?

A

CnH2n+1COOH

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28
Q

Why are carboxylic acids soluble in water?

A
  • form hydrogen bonds with water
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29
Q

Why does solubility decrease as chain length increases?

A
  • increased non-polar proportion of the molecule
  • larger proportion of the molecule cant form hydrogen bonds
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30
Q

What is an acid

A

H+ donor

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31
Q

What does it means when an acid is weak?

A
  • Low concentration of H+ ions (does not fully disassociate)
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32
Q

What do carboxylic acids disassociate to?

A
  • carboxylate anion
  • hydrogen ion
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33
Q

Why are carboxylic acids weak acids?

A
  • they are partially dissociated
34
Q

What does it mean when a carboxylic acid is partially disassociated?

A
  • position of equilibrium is over to the left hand side, so there is a low concentration of H+ present
35
Q

Describe electrons in the carboxylate ion

A
  • delocalised in the Pi system (formed by overlap of p orbitals)
36
Q

Carboxylic acids react in very similar ways to…

A

Inorganic acids

37
Q

What is an acid dissociation constant?

A
  • Ka
  • Quantitative measure of the strength of an acid in solution
38
Q

Why is dimethylpropanoic acid weaker than trifluoroethanoic acid

A

Dimethlypropanoic acid
- Negative charge is more available to act as a base due to the inductive effect of the neighbouring carbon groups
- disassociation less likely to happen, p.o.e to left

Trifluoroethanoic acid
- negative charge less available to act as a base due to the electron withdrawing effect of the fluorine’s
- disassociation more likely to happen, p.o.e to right

39
Q

Give the formula for sodium propanoate

A

CH3CH2COO-Na+

40
Q

What is the functional group for esters?

A
  • COO
41
Q

How are esters produced

A

Alcohols + carboxylic acids -> ester + water

42
Q

What are the conditions needed for esterification?

A
  • warming
  • concentrated acid catalyst - H2SO4
43
Q

Describe an esterification reaction

A
  • the H from the -OH group in alcohol and the -OH from the carboxylic acid join together to make water
  • covalent bond formed between O in the alcohol and C in carboxylic acid group
44
Q

Is esterification reversible?

A

Yes

45
Q

What is acid catalysed hydrolysis?

A

Ester -> alcohol and carboxylic

46
Q

What is acid catalysed hydrolysis?

A

Ester -> alcohol and carboxylic

47
Q

What is base catalysed hydrolysis?

A
  • alcohol and sodium salt of the carboxylic acid are formed - reaction goes to completion (not reversible)
  • sodium or potassium hydroxide are most commonly used
48
Q

What are the uses of ester?

A
  • perfume
  • flavouring
49
Q

Describe properties of esters?

A
  • polar (polar molecules dissolve in them)
  • low bp (so can evaporate easily from mixtures)
  • used as plasticisers
50
Q

Describe esters of glycerol

A
  • oils and fats from animals and vegetables
51
Q

Describe the structure of fats and oils

A

Triglycerides
- three long chain hydrocarbons, unbranched carboxylic acids (fatty acids,) molecule of glycerol

52
Q

What does having unsaturated fatty acids in a triglyceride mean on its melting point?

A
  • less of a region of overlap between the molecule, meaning less vdw forces
  • lower mp
  • unsaturated fats are often liquid at room temperature
53
Q

What happens when a triglyceride is hydrolysed in acidic conditions

A
  • forms glycerol + 3 molecules or original fatty acids
54
Q

What is saponificaiton?

A
  • when triglycerides are hydrolysed under basic conditions
  • forms molecule of glycerol and 3 sodium salts of the original fatty acids
  • salts are used as soaps
55
Q

What do the sodium salts of fatty acids dissociate to

A

Ionic
- Na+
- RCOO-

56
Q

Describe the structure of RCOO-

A
  • non-polar tail
  • polar head
57
Q

Why is RCOO- good as a cleaning agent v

A
  • non polar hydrocarbon chain mixes with grease (hydrophobic)
  • polar COO_ mixes with water (hydrophilic)
  • allows grease and water to mix
58
Q

Is glycerol soluble in water?

A

Yes

59
Q

What are uses of glycerol

A
  • pharmaceutical and cosmetic industries - prevents creams drying out
  • solvent in medicines and is present in toothpaste
  • Solvent in food industry (food colouring)
  • used to plasticise some materials
60
Q

Why was glycerol used as antifreeze

A
  • it can form strong hydrogen bonds with water, lowering freezing point
61
Q

What is the chemical name of glycerol

A

Propane-1,2,3-triol

62
Q

What is biodiesel?

A

Mixture of methyl esters and long chain carboxylic acids

63
Q

How are methyl esters produced?

A

Trans-esterification
- reacting vegetable oils (triglyceride) with 3 equivalents of methanol in presence of a catalyst

64
Q

What are two ways of forming biodiesel?

A
  • esterification of free fatty acids and methanol
  • transesterification of triglyceride and three methanol
65
Q

What is a disadvantedge of using biodiesel over fuel from crude oil

A

Crops for fuel > food

66
Q

Describe the homologous series of acyl chlorides

A
67
Q

What is the general formula for acyl chlorides

A

CnH2n+1COCL

68
Q

What is the functional group of acyl chlorides

A

-COCl

69
Q

What is the nomenclature for acyl chlorides?

A

-oyl chloride

70
Q

What is the general structure of acid anhydride

A
71
Q

What is the general formula for acid anhydrides

A

RCOOCOR’

72
Q

What is the functional group of acid anhydride

A

-COOCO-

73
Q

How do you name acid anhydride

A
  • oic anhydride
74
Q

What mechanism do acylation reactions proceed via?

A

Nucleophilic addition-elimination

75
Q

What are the four nucleophile that can be involved in an acylation reaction

A
  • water - H2O
  • alcohol - ROH
  • ammonia - NH3
  • primary amine - RNH2
76
Q

Describe an acylation reaction

A
  • hydrogen atom in one of the 4 nucleophiles is replaced by acyl group
  • hydrogen atom that left combines with the leaving group in the acyl chloride or acid anhydride
77
Q

What is more reactive acyl chlorides or acid anhydrides?

A

Acyl chlorides
- even though O2 is more electronegative than chloride the oxygen pull on the carbon is diminishes as it is bonded to two C atoms.
- Cl is only taking density from 1 carbon

78
Q

List nucleophiles in the order from most to least reactive

A
  • A 1* amine
  • ammonia
  • alcohol
  • water
79
Q

Display a nucleophilic addition elimination reaction

A
80
Q

What are the advantedges of using acyl chlorides in synthesis

A
  • faster
  • not reversible
  • pure product
81
Q

What are the advantedges of using acid anhydrides in synthesis

A
  • reaction less violent
  • no corrosive HCl fumes formed - less toxic byproduct
  • cheaper

Chemistry (13 decks)

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