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AS Chemistry > Aldehydes and Ketones > Flashcards

Aldehydes and Ketones Flashcards

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1
Q

Functional Group

A

Carbonyl

-C=O

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2
Q

Formation of Aldehydes

A

Alcohol dehyrogenation

Oxidation of a 1° R-X

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3
Q

Formula of Aldehydes

A

Cn H2n+1 CHO

Written in this format to distinguish from Alcohols

R – C = O
|
H

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4
Q

Formula of Ketones

A

O
||
R – C – R’

Rs mustn’t be an H

R’ means that the 2 Rs don’t have to be the same

1st member is propanone

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5
Q

Formation of Ketones

A

Oxidation of a 2° R-X

Can use relux as Ketones can’t be [O] further

Acidified CrO7 2-

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6
Q

Aldehyde - Suffix for naming

A

-al

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7
Q

Ketone - Suffix for naming

A

-one

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8
Q

B.P trends for Aldehydes / Ketones

A

b.p of (corresponding) alkane polar molecule)

As aldehyde gets larger, the effect of the polar C=O becomes less significant

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9
Q

H bonding conditions

A

H is bonded to F/O/N (E.N element)

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10
Q

Solubility of Aldehydes/Ketones

A

Small A/Ks are soluble in H2O

Larger A/Ks become less and less soluble in H2O and more soluble in non polar substances

(effect of polar C=O group)

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11
Q

Uses of aldehydes

A

Methanal in H2O = Formalin

Used to preserve biological specimens/organs/bodies

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12
Q

Natural products

A

Smell in almonds

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13
Q

Uses of ketones

A

Hormones

  • testosterone
  • progesterone

Propanone (Acetone)

  • organic solvent
  • nail polish remover
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14
Q

Reactions of Aldehydes to form Carboxylic Acids

A

Oxidation

a) with H+/Cr2O7 2-
(orange to green)
Cr3+

b) with H+/MnO4-
(purple to colourless)

if not acidified, brown ppt. of MnO2 will form instead of Mn2+

Mn7+ –> Mn2+

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15
Q

Distinguishing between Aldehydes and Ketones

A
  1. Tollen’s Reagent (Silver Mirror Test)

2. Fehling’s Solution

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16
Q

Fehling’s solution

A

alkaline solution (NaOH)

Cu2+ ions

               (OX. Agent) Aldehyde + Cu2+ --> Carboxylic Acid + Cu2O
            blue solution                           red ppt
17
Q

Tollen’s reagent

A

Ammoniacal Silver Nitrate
(excess NH3)

Clean test tube - otherwise black Ag due to [O]

Aldehyde + Ag+ –> Carboxylic Acid + Ag
silver mirror on test tube

18
Q

Reducing reagents for the reduction of Aldehydes and Ketones

A

Sodium tetrahydridoborate - NaBH4 (aq)

Lithium tetrahydrioaluminate - LiAlH4 (aq)
more powerful

19
Q

Reaction of Aldehydes and Ketones with HCN - reactants

A

HCN is generated in situ
(poisonous gas)

NaCN/KCN + dil. H2SO4 generates HCN

==> NaCN/KCN act as a catalyst

20
Q

Overall Reaction Mechanism for addition of HCN to Aldehydes

A

H H O:-
\ NaCN + H2SO4 \ /
C = O ——————-> C (oxoanion)
/ / \
R R CN

                                                      |
                                                      | 

                                              H       OH
                                                  \    /
                                                    C       (hydroxy nitrile) 
                                                  /     \
                                           H3C         CN

Extra electrons from the O- of the oxoanion get a curly arrow pointing to the imaginary line between the H and the O

H is bonded to CN and the bond between these 2 goes to the CN

e.g. 2-hydroxypropanenitrile

21
Q

pH of HCN

A

pH 4 - 5

22
Q

Reduction Reaction of Aldehyde with H2 and Metal Catalyst

A

H H OH
\ Ni/Pt \ /
C = O + H2 ——————-> C
/ / \
R R H

23
Q

Reduction Reaction of Aldehyde with H2 an Metal Catalyst

A

R R OH
\ Ni/Pt \ /
C = O + H2 ——————-> C
/ / \
R R H

24
Q

Reduction reaction of Aldehydes and Ketones with NaBH4 and LiAlH4 conditions

A

NaBH4

  • aqueous alkaline solution e.g NaOH
  • warm with aldehyde/ketone

LiAlH4

  • in dry ether
  • otherwise LiAlH4 will react with H2O
  • r.t
25
Q

Type of reaction between carbonly compounds and HCN?

A

Nucleophilic Addition

C=O is being attacked by an nucleophile ( :CN - )

26
Q

Nitrile group to Carboxylic Acid

A

Hydrolysis

–CN + H+ + H2O –> –COOH + NH4+

27
Q

Nucleophilic Addition Reaction Mechanism - Cyanide ion and Carbonyl

Stage 1

A
  • C = O is polarised

==> C is open to attack by a nucleophile

e.g. - CN:

28
Q

Nucleophilic Addition Reaction Mechanism - Cyanide ion and Carbonyl

Stage 2

A

Intermediary compound formed is highly reactive
( -O: )

and reacts with an H+ ion

(from H2O/HCN/dilute acid)

29
Q

Test to detect presence of carbonyl compounds?

A

Condensation Reaction with

2,4-DNPH

(2,4-Dinitrophenylhydrazine)

30
Q

Carbonyl + 2,4-DNPH: what happens?

A

2 molecules join together and eliminate a small molecule

(here, H2O)

orange ppt.

31
Q

Why doesn’t 2,4-DNPH react with amines, esters & carboxylic acids?

A

extra resonance structure delocalises some of the positive charge away from the carbonyl atom

onto the adjacent hetero-atom

==> the C atom is less prone to attack by the nucleophilic 2,4-DNPH

32
Q

Observation for Tollen’s reagent and Aldehyde

A

Silver mirror formed in the inside of test tube

33
Q

Equation for Tollen’s reagent and Aldehyde

A

Oxidation

RCHO + H2O —-> RCOOH + 2e- + 2H+

Reduction

e- + Ag+ —> Ag(s)

RCHO + 2Ag+ + H2O —-> RCOOH + 2Ag + 2H+

34
Q

Observation for Fehling’s solution and Aldehyde

A

Blue solution to red ppt.

35
Q

Equation for Fehling’s solution and Aldehyde

A

Oxidation

RCHO + H2O —-> RCOOH + 2e- + 2H+

Reduction

2e- + Cu2+ + 2OH- —> Cu2O(s) + H2O

AS Chemistry (5 decks)

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