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Chemistry > Topic 15: Carbonyls, carboxylic acids and chirality > Flashcards

Topic 15: Carbonyls, carboxylic acids and chirality Flashcards

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1
Q

What are stereoisomers?

A
  • compounds with the same structural and molecular formulae
  • have atoms/groups arranged differently in 3-D
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2
Q

What is an optical isomer?

A
  • non-superimposable
  • have a mirror image
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3
Q

What product does a SN1 mechanism produce?

A
  • racemic mixture
  • nucleophile can attack from either side of the carbonyl group, because the reaction site is planar about the C=O bond
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4
Q

What product does a SN2 mechanism produce?

A
  • optical isomer
  • can only attack from one side of the C=O bond
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5
Q

What are the reactions carbonyl compounds undergo?

A
  • Oxidation (aldehydes only)
  • Reduction
  • Nucleophilic addition
  • Iodoform reaction
  • 2,4 - DNPH
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6
Q

What are the four oxidation reactions of aldehydes?

A
  • Potassium dichromate (VI) and dilute sulfuric acid
  • heat under reflux
  • orange —> green (+ result)
  • Tollen’s reagent
  • colourless —> silver mirror (+ result)
  • Fehling’s solution
  • blue solution —> red ppt
  • reduction of Cu(II) to Cu(I) ions
  • Benedict’s reagent
  • blue solution —> red ppt
  • water bath
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7
Q

What reducing agent is used for reduction?

A
  • LiAlH4 / Lithium aluminum hydride
  • in dry ether
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8
Q

What are the steps for nucleophilic addition of carbonyls?

A
  1. KCN added
  2. HCN added
  3. hydroxy nitrile formed
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9
Q

What is Brady’s reagent (2,4-DNPH) used for?

A
  • used for making derivatives
  • to compare carbonly compounds that may have similar boiling/melting points
  • with brady’s they have different melting points
  • positive result: yellow-orange ppt
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10
Q

What is the iodoform reaction?

A
  • NaOH used
  • secondary alcohol or -CH3CO group must be present
  • positive result: yellow ppt due to CHI3 formed
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11
Q

How are carboxylic acids prepared?

A
  1. Oxidation of alcohols/aldehydes
    - potassium dichromate (VI) & sulfuric acid
  2. Hydrolysis of nitriles
    - acid: NH4+ produced, one step
    - alkali: NH3 produced, two steps

BOTH HEAT UNDER REFLUX

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12
Q

What reactions do carboxylic acids undergo?

A
  • Neutralisation
  • carboxylate salt produced
  • Halogenation
  • PCL5 used
  • acyl chloride forms
  • Reduction
  • using LiAlH4
  • primary alcohol formed
  • Esterification
  • use conc. acid catalyst (H2SO4) and heat under reflux
  • ester forms
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13
Q

What reactions do acyl chlorides undergo?

A
  • Water
  • carboxylic acid produced
  • Alcohols
  • ester produced
  • Ammonia
  • amine produced
  • Amines
  • N-substituted amide produced

ALL produce HCl gas (white misty fumes)

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14
Q

What reactions do esters undergo?

A
  • Acid hydrolysis:
  • H2SO4 catalyst
  • ester + water —> carboxylic acid + alcohol
  • one step, reversible reaction
  • Alkali hydrolysis:
  • NaOH used
  • ester + NaOH —> sodium salt + alcohol
  • acid added to convert salt to carboxylic acid
  • two steps, complete reaction
  • Saponification
  • alkali hydrolysis of triglyceride using 3NaOH
  • glycerol and sodium stearate (used in soaps) produced
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15
Q

What is thin-layer chromatography?

A
  • same method as paper, however a glass sheet is used instead
  • silica used as stationary phase
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16
Q

What is column chromatography?

A
  • consists of:
  • stationary phase: liquid/solid that doesn’t move
  • mobile phase: liquid that moves through the stationary phase
  • Advantage: much larger quantities of material can be separated
17
Q

What is HPLC?

A
  • High performance liquid chromatography
  • solvent forced through tube under high pressure
  • stationary phase: silica, a polar solid
  • mobile phase: hexane, a non-polar liquid
18
Q

What affects retention time?

A
  • nature of solvent
  • pressure
  • temp. inside column

the weaker the attraction to the stationary phase, the shorter the retention time

  • retention time is the time take from injection to detection
19
Q

What is gas chromatography?

A
  • stationary phase: solid/liquid coated inside tube
  • mobile phase: INERT gas, e.g; N2, He, CO2
20
Q

What is the standard used in NMR spectra?

A
  • tetramethylsilane (TMS)
  • unreactive, symmetrical, gives a strong signal of zero
  • easy to indentify

Chemistry (7 decks)

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