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Chemistry: the made-up science > Organic Chemistry II > Flashcards

Organic Chemistry II Flashcards

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1
Q

How does optical isomerism arise?

A

Occurs when molecules have a single chiral centre.

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2
Q

What type of isomerism is optical isomerism?

A

Stereoisomerism - same structural formulae but different spacial arrangement.

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3
Q

What’s a similarity and difference between geometric isomerism and optical isomerism?

A

Similarity: both arise from stereoisomerism.

Difference: Optical have atoms arranged to form mirror images of molecules. Geometric has atoms arranged on different sides of a C=C double bond.

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4
Q

What is a racemic mixture?

A

A mixture with equal concentrations of two enantiomers that exhibits no optical activity.
Equimolar amounts of two enantiomers.

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5
Q

What is a chiral molecule?

A
  • When a carbon atom is attached to four different groups
  • No plane of symmetry
  • Cannot be superimposed.
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6
Q

What are enantiomers?

A

Optical isomers that are mirror images of each other.

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7
Q

Define optical activity.

A

When a substance rotates the plane of polarisation of polarised light.

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8
Q

How is monochromatic light polarised?

A
  • Light travels through polariser.
  • One plane of light travels through.
  • All other oscillations are absorbed.
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9
Q

How does a polarimeter measure optical activity?

A
  • Light is polarised.
  • Plane polarised light travels through sample tube with enantiomers inside.
  • Analyser measures the angle at which the plane polarised light rotated at.
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10
Q

Describe the substance if the light is rotated clockwise.

A

Dextrorotatory

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11
Q

Describe the substance if the light is rotated anticlockwise.

A

Laevorotatory

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12
Q

What are the physical properties of enantiomers?

A

Identical physical properties EXCEPT they rotate plane polarised light in opposite directions.

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13
Q

What are the chemical properties of enantiomers?

A

Identical chemical properties EXCEPT they react differently with enantiomers of different substances.

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14
Q

A dextrorotary enantiomer has a rotation of +43. A mixture of the dextrorotatory and laevorotatory enantiomers has a rotation of -10. Describe the composition of the mixture.

A

More laevorotatory as the mixture has an overall negative value of rotation (-10).

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15
Q

What happens in an SN1 mechanism?

A
  • 1 species involved in rate determining step.
  • 2 steps
  • 2nd and 3rd halogenoalkanes
  • Produces racemic mixture with no optical activity.
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16
Q

What happens in an SN2 mechanism?

A
  • 2 species involved in the rate determining step
  • 1 step
  • Occurs in 1st and 2nd halogenoalkanes
  • Produces inverted structure of reactant molecule and halide ion.
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17
Q

What is the formula of the aldehyde functional group?

A

RCHO

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18
Q

What is the formula of the ketone functional group?

A

R-CO-R

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19
Q

What intermolecular forces are in between aldehydes and ketones?

A
  • London forces

- Permanent dipole-dipole attraction (difference in electronegativity between C and O)

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20
Q

What is the functional group of carbonyl compounds?

A

C=O

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21
Q

Why don’t aldehydes and ketones form hydrogen bonds?

A

No H atoms are bonded to atoms with a high electronegativity (N,O,F).

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22
Q

Are aldehydes and ketones soluble in water?

A
  • Short chains are soluble because there is enough energy released when breaking the bonds of water to form H bonds.
  • Longer chains do not release enough energy when breaking bonds between water, therefore, are less energetically profitable. They don’t form H bonds between molecules.
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23
Q

What are the smells of aldehydes?

A
  • Shorter chains = rancid

- Longer chains = pleasant smells like roses, citrus

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24
Q

What are the smells of ketones?

A

Shorter chain ketones smell of solvents

25
Q

What is observed when Fehling’s / Benedict’s solution reacts with aldehydes compounds?

A

Deep blue -> Red

Conversion of copper (II) complex to copper (I) oxide

26
Q

What is observed when acidified potassium dichromate reacts with aldehydes?

A

Orange -> Green

Reduction of chromium +6 to +3

27
Q

What is observed when Tollens’ (ammoniacal silver nitrate) reacts with aldehydes?

A

Colourless soultion -> Silver mirror

Conversion of silver (I) complex to metallic silver

28
Q

How can aldehydes and ketones be reduced to alcohols?

A

Lithium almunium hydride- LiAlH4 [H]

Carbonyl compounds and [H] dissolved in dry ether

29
Q

What is Brady’s / 2,4-DNPH used for and what is the positive result?

A
  • Identify aldehydes and ketones.

- ORANGE precipitate

30
Q

How are derivatives of the 2,4 DNPH used to identify carbonyl compounds?

A
  • Filter, dry and purify derivative
  • Measure melting point
  • Check melting point with data booklet values to identify the initial carbonyl
31
Q

How does iodine in the presence of an alkali identify certain carbonyl compounds?

A

Identifies CH3-C=O

When CH3-C=O is present, CHI3 (triiodomethane) is formed

Yellow precipitate

32
Q

How do shorter chain carboxylic acids react with each other?

A
  • Form dimers

- In absence of a solvent

33
Q

Are carboxylic acids soluble in water?

A
  • Shorter chain carboxylic acids are soluble as they form H bonds with water
  • Longer chains don’t because the hydrocarbon part of the molecule is too large
34
Q

Give two ways in which carboxylic acids can be prepared.

A
  • Oxidation of primary alcohols and aldehydes

- Hydrolysis of nitriles

35
Q

What is produced when carboxylic acids are reduced?

A

PRIMARY ALCOHOLS

Aldehydes can’t be collected as it is immediately reduced to an alcohol

36
Q

What is the reagent used when reducing carboxylic acids?

A

[H] - lithium tetrahydriodialuminate LiAlH4

Used in a solvent of dry ether

37
Q

What is produced when carboxylic acids are neutralised?

A
  • Carboxylate salt

- Water

38
Q

What is produced when carboxylic acids undergo halogenation?

A

Acyl chloride (RCOCl)

39
Q

What is the test for carboxylic acids?

A

carboxylic acid + metal carbonate

CO2 gas is produced so bubbles form

40
Q

What is the reagent used when carboxylic acids undergo halogenation?

A

Phosphorus (V) chloride

41
Q

What are the conditions when carboxylic acids undergo halogenation?

A

ANHYDROUS because PCl5 and acyl chlorides react with water

42
Q

What are the products formed when carboxylic acids and PCl5 react?

A
  • Acyl chloride
  • POCl3
  • HCl
43
Q

What technique would you conduct to obtain an acyl chloride?

A

Fractional distillation of liquid

Acyl chloride and phosphorus trichloride oxide are mixed

44
Q

What are the reactants and conditions used when carboxylic acids undergo esterification?

A
  • Carboxylic acid
  • Alcohol
  • Acid catalyst (conc H2SO4)
45
Q

What are the products of esterification of carboxylic acids?

A
  • Ester

- Water

46
Q

What is the functional group of acyl chlorides?

A

RCOCl

47
Q

What is produced when acyl chlorides and water react?

A
  • Carboxylic acid

- HCl (g)

48
Q

What is produced when acyl chlorides and alcohol react?

A
  • Ester

- HCl (g)

49
Q

What is produced when acyl chlorides and conc ammonia react?

A
  • Amide
  • HCl (g)

Then, ammonia and acidic gas react.

NH3 + HCl -> HN4Cl

50
Q

What is produced when primary amines and acyl chlorides react?

A
  • N substituted amide

- HCl (g)

51
Q

What is produced when secondary amines and acyl chlorides react?

A
  • N,N di substitued amide

- HCl (g)

52
Q

What is the functional group of amines?

A

RNH2

53
Q

What is the functional group of amides?

A

RCONH2

there’s an O. oxIDE -> amIDE

54
Q

What is the functional group of esters?

A

R-COO-R

55
Q

What type of reaction is the esterification of carboxylic acids?

A

REVERSIBLE

56
Q

What is the equation for hydrolysis of esters in acidic solution?

A

ester + water ⇌ carboxylic acid + alcohol

57
Q

What are the equations of the hydrolysis of esters to produce carboxylic acids?

A

1) ester + metal hydroxide → carboxylate salt + metal ion + alcohol
2) carboxylate salt + acid → carboxylic acid

58
Q

When preparing aliphatic amines, why is EXCESS ethanolic ammonia used?

A

To prevent unwanted side reactions from taking place (so that the amine produced does not act as a nucleophile)

59
Q

Why do amino acids exist as solids at room temperature?

A
  • Exist as zwitterions
  • Strong ionic attraction between molecules
  • High m.p

Chemistry: the made-up science (10 decks)

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