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

Organic Chemistry II Flashcards

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
What is observed when Fehling's / Benedict's solution reacts with aldehydes compounds?
Deep blue -> Red Conversion of copper (II) complex to copper (I) oxide
26
What is observed when acidified potassium dichromate reacts with aldehydes?
Orange -> Green Reduction of chromium +6 to +3
27
What is observed when Tollens' (ammoniacal silver nitrate) reacts with aldehydes?
Colourless soultion -> Silver mirror Conversion of silver (I) complex to metallic silver
28
How can aldehydes and ketones be reduced to alcohols?
Lithium almunium hydride- LiAlH4 [H] Carbonyl compounds and [H] dissolved in dry ether
29
What is Brady's / 2,4-DNPH used for and what is the positive result?
- Identify aldehydes and ketones. | - ORANGE precipitate
30
How are derivatives of the 2,4 DNPH used to identify carbonyl compounds?
- Filter, dry and purify derivative - Measure melting point - Check melting point with data booklet values to identify the initial carbonyl
31
How does iodine in the presence of an alkali identify certain carbonyl compounds?
Identifies CH3-C=O When CH3-C=O is present, CHI3 (triiodomethane) is formed Yellow precipitate
32
How do shorter chain carboxylic acids react with each other?
- Form dimers | - In absence of a solvent
33
Are carboxylic acids soluble in water?
- 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
Give two ways in which carboxylic acids can be prepared.
- Oxidation of primary alcohols and aldehydes | - Hydrolysis of nitriles
35
What is produced when carboxylic acids are reduced?
PRIMARY ALCOHOLS | Aldehydes can't be collected as it is immediately reduced to an alcohol
36
What is the reagent used when reducing carboxylic acids?
[H] - lithium tetrahydriodialuminate LiAlH4 Used in a solvent of dry ether
37
What is produced when carboxylic acids are neutralised?
- Carboxylate salt | - Water
38
What is produced when carboxylic acids undergo halogenation?
Acyl chloride (RCOCl)
39
What is the test for carboxylic acids?
carboxylic acid + metal carbonate CO2 gas is produced so bubbles form
40
What is the reagent used when carboxylic acids undergo halogenation?
Phosphorus (V) chloride
41
What are the conditions when carboxylic acids undergo halogenation?
ANHYDROUS because PCl5 and acyl chlorides react with water
42
What are the products formed when carboxylic acids and PCl5 react?
- Acyl chloride - POCl3 - HCl
43
What technique would you conduct to obtain an acyl chloride?
Fractional distillation of liquid | Acyl chloride and phosphorus trichloride oxide are mixed
44
What are the reactants and conditions used when carboxylic acids undergo esterification?
- Carboxylic acid - Alcohol - Acid catalyst (conc H2SO4)
45
What are the products of esterification of carboxylic acids?
- Ester | - Water
46
What is the functional group of acyl chlorides?
RCOCl
47
What is produced when acyl chlorides and water react?
- Carboxylic acid | - HCl (g)
48
What is produced when acyl chlorides and alcohol react?
- Ester | - HCl (g)
49
What is produced when acyl chlorides and conc ammonia react?
- Amide - HCl (g) Then, ammonia and acidic gas react. NH3 + HCl -> HN4Cl
50
What is produced when primary amines and acyl chlorides react?
- N substituted amide | - HCl (g)
51
What is produced when secondary amines and acyl chlorides react?
- N,N di substitued amide | - HCl (g)
52
What is the functional group of amines?
RNH2
53
What is the functional group of amides?
RCONH2 | there's an O. oxIDE -> amIDE
54
What is the functional group of esters?
R-COO-R
55
What type of reaction is the esterification of carboxylic acids?
REVERSIBLE
56
What is the equation for hydrolysis of esters in acidic solution?
ester + water ⇌ carboxylic acid + alcohol
57
What are the equations of the hydrolysis of esters to produce carboxylic acids?
1) ester + metal hydroxide → carboxylate salt + metal ion + alcohol 2) carboxylate salt + acid → carboxylic acid
58
When preparing aliphatic amines, why is EXCESS ethanolic ammonia used?
To prevent unwanted side reactions from taking place (so that the amine produced does not act as a nucleophile)
59
Why do amino acids exist as solids at room temperature?
- Exist as zwitterions - Strong ionic attraction between molecules - High m.p

Chemistry: the made-up science (10 decks)

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