CARBONYLS Flashcards

1
Q

why are aldehydes and ketones described as unsaturated

A

they contain a carbon-oxygen double bond

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2
Q

tollens + aldehyde

A

forms a silver mirror

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3
Q

tollens + ketone

A

no reaction as ketone cannot be further oxidised

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4
Q

acidified K2Cr2O7 + aldehyde

A

orange –> green colour change

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5
Q

acidified K2Cr2O7 + ketone

A

no reaction as ketone cannot be further oxidised

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6
Q

what does the reduction of an aldehyde produce

A

1º alcohol

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7
Q

what does the reduction of a ketone produce

A

2º alcohol

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8
Q

what reagents do you use to reduce a carbonyl by nucleophilic substitution

A

NaBH4 in warm aq solution

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9
Q

carbonyl compound - nuc add. w/ nitrile ions

  • reagents
  • conditions
  • nucleophile
  • product
  • eq.
A
  • reagents = hydrogen cyanide HCN
  • conditions = reflux in alkaline conditions
  • nucleophile = cyanide ion CN:-
  • product = hydroxynitrile
  • eq.= CH3CHO + HCN –> CH3CH(OH)CN
  • addition of HCN
  • opical isomerism when CN-attacks from above vs below
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10
Q

why do the conditions need to be alkaline during nuc add. w/ nitrile ions

A

NaOH (aq) allows H+ to react w/ OH- to give water, .:. the equilibrium will shift to the right, producing more H+ and CN- (the nucleophile)

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11
Q

describe the mechanism for nuc add. w/ nitrile ions

A

STEP 1 :
CN- acts as a nucleophile and attacks the slightly positive C (from C=O)
1 of the C=O bonds break: e- pair goes to O

STEP 2:
A pair of e- used to form bond w/ H+
overall there has been an addition of HCN

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12
Q

2,4-DNPH + aldehyde

A

orange/yellow ppt forms

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13
Q

2,4-DNPH + ketone

A

orange/yellow ppt forms

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14
Q

test for carbonyls

A

2,4-DNPH –> orange/yellow ppt forms

2,4-DNPH = Brady’s reagent

test proves presence but does not identify aldehyde or ketone

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15
Q

how can you identify the carbonyl from the ppt formed after reacting it with Brady’s reagent/2,4-DNPH

A

recrystalise ppt in minimum amount of hot solvent

take the melting point of pure, dry crystal

compare to database + identify

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16
Q

how to make tollens

A

add NaOH to AgNO3 - brown ppt forms

and NH3 (aq) untill ppt dissolves

[H3N-Ag-NH3]