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Chemistry A Level > 17 - Organic II > Flashcards

17 - Organic II Flashcards

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1
Q

why do we get optical isomerism

A
  • chiral centre

- in a molecule with asymmetrical carbon atoms

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2
Q

what are optical isomers

A

enantiomers which are object and non-superimposable mirror images

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3
Q

how do you identify enantiomers

A
  • pass plane polarised light through the beaker

- will rotate the plane by equal angles in opposite directions

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4
Q

what is a racemic mixture

A

a mixture with equal amounts of each enantiomer

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5
Q

optical isomers in SN1 reactions

A
  • carbocation is planar
  • nucleophile can attack from either side
  • makes a racemic mixture
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6
Q

optical isomers in SN2 reactions

A
  • nucelophile always attacks the carbon from the opposite side to the group that’s leaving
  • always end up with the opposite optical isomer
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7
Q

solubility of aldehydes and ketones

A
  • soluble

- the O can form hydrogen bonds with water

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8
Q

melting and boiling points of aldehydes and ketones

A
  • low

- can’t form intermolecular hydrogen bonds

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9
Q

what can aldehydes and ketones be oxidised and reduced to

A
  • ketones can be reduced to a secondary alcohol
  • aldehydes can be reduced to a primary alcohol
  • aldehydes can be oxidised to carboxylic acids
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10
Q

draw mechanism for reduction of aldehydes and ketones

A
  • LiAlH4 dissolved in dry ether

- check mechanism

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11
Q

iodoform reaction

A
  • reagent is iodine in the presence of alkali
  • tests for methylketones, ethanal and secondary alcohols
  • gives pale yellow precipitate with antiseptic smell
  • check reaction
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12
Q

2,4-DNPH reaction

A
  • tests for aldehydes and ketones
  • forms yellow/orange precipitate
  • can identify the compound by filtering the ppt, purify by recrystallisation, measure melting point, compare to known data.
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13
Q

draw the mechanism for nucleophilic addition of KCN

A
  • check mechanism

- CN- acts as a catalyst

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14
Q

how can you make HCN for the nucleophilic addition reaction

A
  • H2SO4 + KCN –> KHSO4 + HCN
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15
Q

Tollens’ reagent reaction

A
  • tests for aldehydes
  • is an alkaline solution of Ag+
  • warm with R-CHO –> R-COOH –> R-COO-
  • forms a silver mirror on the test tube due to formation of Ag(s)
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16
Q

how to make Tollens’ reagent

A
  • NaOH + AgNO3 (aq) –> Ag2O (s)

- Ag2O + NH3 –> [Ag(NH3)2]+

17
Q

Fehling’s/ Benedict’s Solution reaction

A
  • tests for aldehydes
  • is an alkaline solution of Cu2+
  • warm with R-CHO –> R-COOH –> R-COO-
  • Cu2+ –> Cu2O
  • blue solution to red precipitate
18
Q

oxidation of aldehydes back to carboxylic acids

A
  • acidified potassium dichromate (VI) K2Cr2O7
  • Cr2O7- –> Cr3+
  • orange solution to green solution
19
Q

physical properties of carboxylic acids

A
  • good at hydrogen bonding due to two lone pairs on each oxygen
  • small ones soluble, but not large as only functional group can hydrogen bond
  • can form dimers (draw) resulting in twice the number of london forces, so high boiling points
20
Q

two ways to make a carboxylic acid

A
  • hydrolysis of a nitrile, heat under reflux with dilute HCl
  • oxidise aldehydes or alcohols, add acidified potassium dichromate
  • heat under reflux for alcohols
21
Q

reduction of a carboxylic acid

A
  • add LiAlH4 in dry ether

- goes from carboxylic acid –> aldehyde –> alcohol

22
Q

carboxylic acid + PCl5

A
  • makes an acyl chloride, replacing OH with Cl and POCl3
23
Q

how to make an acyl chloride

A
  • carboxylic acid + PCl5

- produces acyl chloride and POCl3

24
Q

write out equation for ethanoic acid + NaOH

A

check

25
Q

write out equation for ethanoic acid + CaO

A

check

26
Q

slow way to make an ester

A
  • carboxylic acid + alcohol –> ester + H2O
  • requires concentrated H2SO4 catalyst
  • reversible reaction so incomplete and low yield
27
Q

what are esters used for

A

flavourings and perfumes

28
Q

fast way to make an ester

A
  • acyl chloride + alcohol –> ester + HCl

- fast and complete

29
Q

acidic hydrolysis of an ester

A
  • ester + H2O –> alcohol + carboxylic acid
  • slow as it needs dilute H2SO4 catalyst
  • incomplete so low yield
30
Q

alkaline hydrolysis of an ester

A
  • ester + NaOH –> salt + alcohol
  • add HCl to turn salt into carboxylic acid
  • fast and complete reaction
31
Q

how to make a polyester

A

condensation reaction with an alcohol and carboxylic acid, each with 2 functional groups on each

Chemistry A Level (14 decks)

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