Chapter 18 - ketones and aldehydes

Ketones

R - C (= O) - R

Carboxylic acid

R - C ( = O) - OH

Ester

R - C ( = O ) - O - R

Aldehydes 

Acid Chlorides

Amides 

Structure of carbonyl group

• SP² hybridized 

• the C = O is shorter and stronger than more polar the C = C Bond in alkene 

solubility of ketones and aldehydes 

• Good solvent for alcohols 

• The oxygen in the carbonyl group can form hydrogen bonds with O—H or N—H groups.

• Small ketones and aldehydes (like acetone and acetaldehyde) mix completely with water.

Grignard reagent

Reagent :

1. R - mgX

2. H30

3. Na₂Cr₂O_7, H₂SO₄

Starting

• with an aldehyde

Mechanism 

• the R - MgX attacks the double bond of O and the R group attaches and MGX leaves. 

• H30 (acid ) give an H to the O making it in alcohol 

• Na2Cr2O7 takes the Hydrogen of the alcohol making it a ketone

End product: 

• ketone

Oxidation of primary alcohols to aldehyde

Starting product: primary alcohol

Reagent:

• PCC (Pyridinium chlorochromate)

• swern

• DMP

1. PCC is used to oxidize primary alcohol to aldehydes 

End product: aldehyde  

Ozonolysis Of alkenes

Reagent: 

1. O₃ ,

2. Reductions (CH3)₂S (DMS)

Starting product: Alkenes 

• Brakes the double bond followed by a reduction 

End Product: Ketones and Aldehydes 

Friedel craft reduction

Starting: Aromatic ring

Reagent: 

• Acid halide (RCOCl)

• Lewis Acid (AlCl₃)

Steps 

1. Lewis acid takes the Halide from R-C(=O)-CL

2. Carbocation is formed and benzene attacks it and then its added on 

Reaction between an acyl halide and an

aromatic ring will produce a ketone.

Reduction of Nitriles to Aldehydes

Starting product: nitrile (R - C≡N)

Reagent: (i - Bu)₂ ALH → aluminum hydrides 

or DIBAL - H 

• H₃O +

• Convertes nitriles to aldehydes  

Aldehydes from acid chloride

Starting Product:

• Acid chloride ( R - C (=O) - Cl 

Reagent: 

• Li+ -AlH(O t-but)₃ → Lithium aluminum tri(t-butoxy)hydride

End product: aldehyde 

Reactivity Aldehydes vs Ketones

Aldehydes are more reactive then Ketones

The Wittig Reaction

Starting product: Keton or aldehyde

Reagent: Phosphorus ylide 

• Converts a carbonyl group into a new C=C double bond 

• Phosphorus yield is used a the nucleophile in the reaction 

Mechanism:

• the Phosphorus ylide attacks the keton or aldehyde

• the double bond of O breaks and it is left as negative O- (betaine)

• The O forms a bond with the adjacent Ph₃P (Oxaphosphetane formation)

• but this will collapse and the Oxygen will break its bond with carbon and leave with Ph3P and the carbon will become a double bond and then form a carbonyl (ketone or aldehyde ) see down below.

SN2 mechanism 

Preparation of Phosphorus Yield (Wittig reaction)

Starting: 

• triphenylphosphine 

Reagent: 

• alkyl halide R - C - X

Basea: 

• n-Butyllithium (n-BuLi)

• Sodium hydride (NaH)

• Potassium tert-butoxide (t-BuOK)

Mechanism 

1. triphenylphosphine attacks Alkyl halide 

2. the triphenylphosphine kicks the X (halide) out and a new bond is formed 

3. The base takes a hydrogen from carbon.

Hydration of Ketone + Aldehyde 

Reagent:

• H₂O 

Starting Product 

• Ketone

• Aldehyde 

End product:

2 Alcohol group attached to the carbon where the double bond of Oxygen was originally

• geminal diol

Acid-Catalyzed Hydration of Carbonyls

Reagent:

• H₃O 

• H₂O

Starting product 

• Ketone or

• Aldehyde 

Mechanism 

• H₃O give a hydrogen to O (oxygen) 

• Water (H₂O) comes in and attacks carbon 

• Another water comes in and protonates ( The H that was from the water)  

Base-Catalyzed Hydration of Carbonyls

Reagent: 

• Hydroxide ion (OH^-) 

• H₂O

Starting product:

• Ketone 

• Aldehyde

Mechansium:

1. the base (OH ) attacks Carbon

2. the double bond breaks making O^-

3. Water comes in and Oxygen takes a hydrogen from water

End product 

• two –OH groups on the same carbon (geminal diol)

Cyanohydrin Formation

Reagent

• ^-:C≡N (Hydrogen cyanide)

can also be seen as NaCN

• H - C≡N

Starting product 

• ketone

• Aldehyde 

Mechansium 

1. The CN⁻ attacks the carbon of the carbonyl (C=O)

2. The oxygen from the carbonyl grabs a proton (H⁺) from HCN or water.

End product:

• cyanohydrin (–OH and –CN attached to the same carbon).

Formation of Imines

Reagent :

• 1 amine or ammonia (R - NH₂)

• H⁺

Starting: Ketone/Aldehyde 

Mechanism:

Step 1: Acid-catalyzed addition

1. The hydrogen form the acid from H+ is taken by Oxygen. 

2. the double bond of of O breaks 

3. The nitrogen of the amine attacks the carbonyl carbon.

4. Water comes in and takes an H from RNH2 making it R- NH. 

Step 2: Acid-catalyzed dehydration

1. Another H+ is introduces and Oxygen taking a H  makes it a L.G H₂O

2. A double bond with carbon and nitrogen from

3. Water comes in and take an H from R- NH

Formation of Acetals

Reagent

• 2 R - OH 

• H+ (H - OTs) 

Starting 

• aldehyde 

• Ketone  

Mechanism:

• Step 1: Carbonyl oxygen gets protonated (this is before the alcohol attacks).

• Step 2: Alcohol attacks the carbonyl carbon → tetrahedral intermediate → hemiacetal.

  

• Step 3: Another H+ and Oxygen takes another hydrogen make it H2) and it leaves 

• Step 4: Second alcohol attacks → acetal formed.

• another alcohol comes in and takes a hydrogen  

Hemiacetal Formation (intermediate step) 

Starting:

Ketone/ Aldehyde 

Reagent: 

• H+ 

• R- OH 

Mechanism: 

1. The oxygen takes an H from H+ 

2. the first alcohol comes in and attacks the carbon 

3. another alcohol comes in a takes the hydrogent from the first alcohol.  

Hydrolysis of Acetals

Starting product:

• Acetal 

  

Reagent: 

• Water (H2O)

• Acid catalyst (H⁺)

End product: 

• The original aldehyde or ketone

Cyclic Acetals

Starting

• Aldehyde or Ketone (R–C=O)

Reagent: 

• H+

• Diol

• A diol reacts with a carbonyl to make a ring-shaped (cyclic) acetal.

• The reaction can go backward (it’s reversible).

• Chemists use this to protect aldehydes or ketones during other reactions.

Acetal with NaBH4

• Acetal will not react with NaBH4

• so is this example only the ketone will reduced

• and the Acetal will experience hydrolysis and will protonate the alcohol and remove the acetal to aldehyde

Sodium Borohydride

Reduction reagent

• NaBH₄

1. Reduces keton to secondary alcohols and aldehydes to 1alcohols

2. Cant reduce ester or carboxylic acid, acyl chlorides or amides

• convertes the Oxygen to an alcohol 

Lithium Aluminum Hydride

Reduction reagent

• LiALH₄

• Ether

Can only reduce carbonyl (ketone and aldehyde) because it is a very strong reducing agent

• Makes O → OH

Catalytic Hydrogenation 

Reducing reagent 

• NiH₂

1. it will attack the alkene (C = C ) first

2. then it attacks the carbonyl

Deoxygenation of Ketones and Aldehydes

Reagent

• H₂

The Clemmensen reduction or the Wolff–Kishner

reduction can be used to deoxygenate ketones and aldehydes

• Adds two hydrogen the same carbon so removes the double bond with Oxygen