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A Level - Chemistry > 17: Chirality and Carbonyls > Flashcards

17: Chirality and Carbonyls Flashcards

1
Q

Define optical isomers

A

Isomers of which one is the non-superimposable mirror image of the other

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2
Q

What is chirality caused by?

A

A carbon with 4 different groups attached to it

Called a chiral centre

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3
Q

What are optical isomers known as?

A

Enantiomers

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4
Q

Why are chiral molecules known as optical isomers?

A

The isomer can rotate the plane of polarisation of plane-polarised monochromatic light

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5
Q

Define a racemic mixture

A

A solution containing equal amounts of 2 isomers

Does not rotate plane of plane-polarised monochromatic light

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6
Q

Compare and contrast enantiomers

A

Identical physical and chemical properties

React differently with plane-polarised light

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7
Q

What is the structure of an aldehyde functional group?

A

Carbon bonded to a H, double bond O, and a R group

Found on the end of a chain

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8
Q

What is the structure of a ketone functional group?

A

Carbon with a double O bond, and two R groups

Found in the middle of a carbon chain

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9
Q

What is significant about a carbon oxygen double bond?

A

Oxygen is more electronegative, causes a polar bond

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10
Q

Why can aldehydes and ketones not hydrogen bond with each other?

A

No hydrogen atoms bonded to the oxygen atoms

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11
Q

Are ketones and aldehydes soluble in water?

A

Small aldehydes and ketones are soluble in water

Solubility decreases as carbon chain increases

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12
Q

Why are only small carbonyls soluble in water?

A

They can hydrogen bond with water molecules
Hydrocarbon tails are hydrophobic
Solubility breaks hydrogen bonding in water, and if they are not replaced by strong inter molecular bonds then it will be insoluble
Hydrocarbon chains only have id-id so the longer, the less soluble

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13
Q

What is the main form of reactions carbonyls undergo and why?

A

Nucleophillic addition
Condensation
Due to 𝛿+ carbon atom attracting nucleophiles

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14
Q

What is the test for a carbonyl group?

A

Adding 2,4-DNP
Forms yellow crystals (2,4-dinitrophenylhydrazone crystals)
Condensation reaction

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15
Q

What are the 3 oxidation tests for aldehydes (not ketones)?

A

Tollens reagent - ammonial silver nitrate
Fehlings solution - copper 2+ ions
Acidified dichromate - H+/Cr2O7 2-

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16
Q

Why are oxidation tests used to test for aldehydes not ketones?

A

Aldehydes can be further oxides ex to carboxylic acids

Ketones cannot be futher oxidised

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17
Q

How is tollens reagent formed?

A

Ag+ + 2NH3 -> Ag[NH3]2 +

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18
Q

What are the half equations for the tollens reagent in presence of an aldehyde?

A

R-CHO + H2O -> R-COOH + 2e + 2H+
Ag+ + e -> Ag

Combined:
R-CHO + H2O + 2Ag+ -> R-COOH + 2Ag + 2H+

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19
Q

What is observed in the Tollens reagent test in the presence of an aldehyde?

A

A silver mirror will form on the inside of the test tube

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20
Q

What is in fehlings solution?

A

Solution of Cu2+ ions

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21
Q

What is reduced in the Fehlings test?

A

Cu2+ -> Cu+

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22
Q

What are the half equations for the Fehlings test?

A

R-CHO + H2O -> R-COOH + 2e + 2H+
2Cu2+ + H2O + 2e -> Cu2O + 2H+

Combined:
R-CHO + 2H2O + 2Cu -> R-COOH + Cu2O+ 4H+

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23
Q

What is the colour change if acidified potassium dichromate is in solution with an aldehyde?

A

Orange to green

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24
Q

What is the change in oxidation state when potassium dichromate is oxidised?

A

Cr6+ -> Cr3+

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25
Q

What is the half equation for potassium dichromate reacting with an aldehyde?

A

Cr2O7 2- + 14H+ + 6e -> 2Cr 3+ + 7H2O
R-CHO + H2O -> R-COOH + 2e + 2H+

Combined:
3R-CHO + Cr2O7 2- + 8H+ -> 3R-COOH + 2H2O + 2Cr 3+

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26
Q

How does the increase of chain length effect the oxidation of an aldehyde?

A

Slower they react

The aldehydes have less reducing power

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27
Q

Why do ketones not give a positive result in reducing tests?

A

They cannot be oxidised easily

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28
Q

What is the iodoform (triiodomethane) test?

A

Tests for the methyl carbonyl and methyl OH groups

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29
Q

What are the reagents in the iodoform test?

A

Iodine and sodium hydroxide

30
Q

What is the sign for a positive iodoform test?

A

CHI3 - Pale yellow precipitate

Antiseptic smell

31
Q

What is the equation for the iodoform test?

A

R-CHO + 3I2 + 4NaOH -> CHI3 + HCOO-Na+ + 3NaI + 3H2O

32
Q

What is produced when cyanide and hydrogen cyanide is added to a carbonyl?

A

Carbonyl -> organic compound with a cyandide and alcohol

33
Q

What are the steps in the nucleophillic addition of cyanide to a ketone?

A

Lone pair on CN- attacks 𝛿+ Carbon
One of double bond breaks and both electrons goes to the Oxygen
Lone pair on oxygen forms bond with Hydrogen from HCN
CN- ion and organic product is left

34
Q

What can the product of the addition of cyanide be converted into?

A

Anime - LiAlH4 and dry ether

Carboxylic acid - H2O/H+

35
Q

What is LiAlH4 and what does it do?

A

Lithium aluminium hydride
Reduces C=O bond to OH
Reduces CN bond to NH2

36
Q

What is the first step in the addition of HCN to a carbonyl?

A

Attack by CN- of 𝛿+ on C=O

37
Q

What are the similarities and differences of enantiomers?

A

Same molecular formula
Same structural formula
Atoms in different position in 3D space

38
Q

Why is SN2 called this?

A

SN - Nucleophillic substitution

2 - 2 species involved in the first step

39
Q

What happens to optical isomers in an SN2 reaction?

A

The molecule will retain its chirality

40
Q

What type of halogenoalkanes undergo SN2?

A

Primary

41
Q

What type of halogenoalkanes undergo SN1?

A

Tertiary

42
Q

What is the effect of SN1 reactions on optical isomers?

A

Racemic mix is formed

Intermediate is trigonal planar so the nucleophile can be added on either side

43
Q

What is the effect of the SN2 mechanism on optical isomers?

A

No effect on optical isomers

Single enantiomer reactant produces single enantiomer product

44
Q

What is the difference between addition and condensation polymerisation?

A

Addition - All monomer atoms present in polymer

Condensation - Water lost

45
Q

What are the typical monomers of condensation polymerisation?

A

Diol + dicarboxylic acids

46
Q

How are carboxylic acids arranged without water?

A

Dimers - hydrogen bond with another carboxylic acid

47
Q

How is a carboxylic acid produced from a nitrile?

A

Reflux with dilute acid in aqueous environments

48
Q

What is the general formula for the production of carboxylic acids from nitriles?

A

R-CN + H2O + H+ -> R-COOH + NH4+

49
Q

How do carboxylic acid reaction with sodium hydroxide?

A

Acid + Alkali -> Salt + Water

R-COOH + NaOH -> R-COO- Na+ + H2O

50
Q

How do carboxylic acids react with alcohols?

A

Carboxylic acid + Alcohol -> Ester + Water

Presence of acid catalyst needed - conc sulphuric acid

51
Q

What is the reaction type of the formation of a ester?

A

Esterification - Adddition elimination

52
Q

What are the conditions for esterification?

A

Heated with acid catalyst (sulphuric acid)

Slow and reversible reaction

53
Q

How are esters named?

A

Take name of alcohol and replace “anol” with “yl”

Second word is carboxylic acid, replace “oic” with “anoate”

54
Q

What occurs in the reaction between LiAlH4 and carboxylic acids?

A

Carboxylic acid + H- -> Alcohol (OH)

Organic solvent - dry ether

55
Q

How does LiAlH4 work?

A

H- ion acts as a nucleophile

Will reduce water so organic solvent must be used

56
Q

How are esters made into alcohols and carboxylic acids?

A

Hydrolysed

57
Q

How are acyl chlorides formed?

A

R-COOH + PCl5 -> R-OCl + POCl3 + HCl

Releases steamy fumes of HCl

58
Q

How can the presence of HCl fumes be confirmed?

A

Will produce white smoke in presence of ammonia

Forms ammonium chloride

59
Q

What is the functional group of acyl chlorides?

A

R-O-Cl

60
Q

How do acyl chlorides typically react?

A

Nucelophilic substitution

61
Q

What is produced when acyl chlorides react with water?

A

Carboxlyic acid + HCl

62
Q

What is the defining property of acyl chlorides?

A

High reactivity
Caused by large difference in electronegativity between Cl and C - draws electrons away creating a larger positive charge

63
Q

What is a common alternative to acyl chlorides?

A

Ethanoic anhydride

64
Q

What is the problem when acyl chlorides being used as a reactant?

A

Toxic fumes produced

Fume cupboard should be used

65
Q

Which bonds are broken and made in esterification?

A

Broken: C-O, O-H
Made: C-O, O-H

66
Q

How do esters react with NaOH?

A

R-O-R’ + NaOH -> RCOONa + R’-OH

67
Q

What is produced when acyl chlorides react with alcohols (OH)?

A

Ester + HCl

68
Q

What is produced when acyl chlorides react with amines?

A

N-substituted amide + HCl

69
Q

What is produced when acyl chlorides react with concentrated ammonia?

A

Amide + HCl

70
Q

What are the reactions like which involve acyl chlorides?

A

Vigorous reaction at room temp

A Level - Chemistry (26 decks)

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