1. Aldehydes and Ketones

2. Structures of Aldehydes and Ketones
Both aldehydes and ketones contain a carbonyl group
Aldehydes have at least one H attached, while ketones have two C’s attached to the carbonyl
A carbonyl consists of a C double-bonded to an O
Like in an alkene, the double bond consists of one sigma and one pi bond
The carbonyl is a very polar group
- O is more electronegative than C, so C-O bonds are polar
- Also, the carbonyl has two resonance forms
- This polarity makes carbonyls chemically reactive

3. Naming Ketones Parent name ends in -one
Find longest chain containing the carbonyl group
Number C’s starting at end nearest carbonyl group
Locate and number substituents and give full name
- use a number to indicate position of carbonyl group
- cyclic ketones have cyclo- before the parent name; numbering begins at the carbonyl group, going in direction that gives substituents lowest possible numbers
- use a prefix (di-, tri-) to indicate multiple carbonyl groups in a compound

4. IUPAC nomenclature of ketones
Common system of ketones:

5. Naming Aldehydes Parent name ends in -al
Find longest chain containing the carbonyl group
Number C’s starting at end nearest carbonyl group
Locate and number substituents and give full name
- aldehydes take precedence over ketones and alcohols in naming
- ketones are called oxo as a secondary group
- alcohols are called hydroxy as a secondary group
- the smallest aldehydes are usually named with common names
- we will not name cyclic aldehydes (except benzaldehyde)

6. Naming Aldehydes

7. Nomenclature
because the carbonyl group of an aldehyde can only be at the end of a parent chain and numbering must start with it as carbon-1, there is no need to use a number to locate the aldehyde group
for unsaturated aldehydes, indicate the presence of a carbon-carbon double bond and an aldehyde by changing the ending of the parent alkane from -ane to -enal; show the location of the carbon-carbon double bond by the number of its first carbon

8. Nomenclature
the IUPAC system retains common names for some aldehydes, including these three

9. 2) Common name

10. Physical Properties of Aldehydes and Ketones
Because the carbonyl group is polar, aldehydes and ketones have higher boiling points than hydrocarbons
However, they have no H attached to the O, so do not have hydrogen bonding, and have lower boiling points than alcohols
Like ethers, aldehydes and ketones can hydrogen bond with water, so those with less than 5 carbons are generally soluble in water
Aldehydes and ketones can be flammable and/or toxic, though generally not highly so
They usually have strong odors, and are often used as flavorings or scents

13. Preparation of aldehydes & ketones:
From acid chloride:
This method is called Rosemund reduction.

14. (2) From geminal dihalide:
Question: convert toluene to benzaldehyde
Answer

15. (3) Partial decarboxylation of salt of acids:
Question: Show how could you prepare the following
To prepare
by above method, we use two molecules

16. (4) From nitrile:
a- Aldehyde:
b- Ketone

17. (5) Oxidation of alcohols:
a- Aldehyde: From oxidation of primary alcohol.
b- Ketone: From oxidation of secondary alcohol.

18. (6) Ozonolysis of alkene :H
(7) Hydration of alkyne :
Only other alkyne except acetylene will give ketone

19. Synthesis of aromatic ketones via Friedel-Crafts acylation:
E.g. Acetophenone
Form benzophenone

20. Synthesis of benzaldehyde
Gattermann-Koch aldehyde synthesis
b) Gattermann aldehyde synthesis

21. Chemical reactions of aldehydes & Ketones
A-Type I of reaction (Addition reaction)
Examples of this addition is addition of HCN, H2, RMgX, HOH, NaSO3H

22. Formation of hemiacetals and acetals
Addition of Alcohols to Aldehydes and Ketones
Alcohols can add to aldehydes and ketones using an acid catalyst
Addition of 2 alcohols produces an acetal (a diether)
The reaction intermediate, after addition of one alcohol, is a hemiacetal (not usually isolated)
This is a reversible reaction
- removal of H2O favors acetal
- addition of H2O favors aldehyde or ketone
Acetals are often used as protecting groups in organic synthesis

23. B-Type II of reaction [addition reaction followed by loss of H2O]
e.g. (Condensation with amines)
Examples:

25. 2- Cannizaro reaction:
- It occurs between two aldehydes with no α-hydrogen in presence of base to give an alc. and an acid.
The adduct of an aldehyde and OH can transfer hydride ion to another aldehyde C=O resulting in a simultaneous oxidation and reduction (disproportionation)

26. Oxidation of Aldehydes
Recall that aldehydes and ketones are formed by the oxidation of primary and secondary alcohols, respectively
Also recall that aldehydes are readily oxidized to carboxylic acids, but ketones are not
Tollens’ reagent (silver nitrate plus ammonia) can be used to distinguish between ketones and aldehydes
- with aldehydes the Ag2+ is reduced to elemental silver, which forms a mirror-like coat on the reaction container
Sugars (like glucose) often contain a hydroxy group adjacent to an aldehyde
- Benedict’s reagent (Fehlings reagent) (CuSO4) can be used to test for this type of aldehyde; the blue Cu2+ forms Cu2O, a red solid

27. Oxidation
Aldehydes are oxidized to carboxylic acids by a variety of oxidizing agents, including potassium dichromate
liquid aldehydes are so sensitive to oxidation by O2 of the air that they must be protected from contact with air during storage

28. Oxidation
Ketones resist oxidation by most oxidizing agents, including potassium dichromate and molecular oxygen
Tollens’ reagent is specific for the oxidation of aldehydes; if done properly, silver deposits on the walls of the container as a silver mirror

31. Reduction of Aldehydes and Ketones
Reduction can be defined as a loss in bonds to O or a gain in bonds to H
Aldehydes and ketones can be reduced to form alcohols
- Aldehydes form primary alcohols
- ketones form secondary alcohols
Many different reducing agents can be used, including H2, LiAlH4 (lithium aluminum hydride) and NaBH4 (sodium borohydride)
However, NaBH4 is usually the reagent of choice
- hydrogenation will also reduce alkenes and alkynes if present
- LiAlH4 is more reactive than NaBH4, but reacts violently with water and explodes when heated above 120º C

32. Reduction
The carbonyl group of an aldehyde or ketone is reduced to an -CHOH group by hydrogen in the presence of a transition-metal catalyst
reduction of an aldehyde gives a primary alcohol
reduction a ketone gives a secondary alcohol

33. Reduction
reduction by NaBH4 does not affect a carbon-carbon double bond

34. Addition of Water to Aldehydes and Ketones
H2O can add across the carbonyl of an aldehyde or a ketone, similar to the addition of H2O to an alkene
A partial positive H from water bonds to the partial negative carbonyl O, and the partial negative O from water bonds to the partial positive carbonyl C
The product of this reversible reaction is a hydrate (a 1,1-diol)
In general, the equilibrium favors the carbonyl compound, but for some small aldehydes the hydrate is favored
The reaction can be catalyzed by either acid or base

35. Mechanism of Acid-Catalyzed Hydration of Formaldehyde
First, the carbonyl O is protonated by the acid catalyst
Next, H2O attacks the carbonyl carbon to form a protonated hydrate
Finally, H2O removes the proton to form the hydrate

36. Addition of Alcohols to Aldehydes and Ketones
Alcohols can add to aldehydes and ketones using an acid catalyst
Addition of 2 alcohols produces an acetal (a diether)
The reaction intermediate, after addition of one alcohol, is a hemiacetal (not usually isolated)
This is a reversible reaction
- removal of H2O favors acetal
- addition of H2O favors aldehyde or ketone
Acetals are often used as protecting groups in organic synthesis

37. 2- Reduction to hydrocarbon:
For examples;

38. a- Clemmensen reduction:
b- Walf-Kishner reduction:

39. Keto-Enol Tautomerism
A carbon atom adjacent to a carbonyl group is called an a-carbon, and a hydrogen atom bonded to it is called an a-hydrogen

40. Keto-Enol Tautomerism
A carbonyl compound that has a hydrogen on an a-carbon is in equilibrium with a constitutional isomer called an enol
the name “enol” is derived from the IUPAC designation of it as both an alkene (-en-) and an alcohol (-ol)
in a keto-enol equilibrium, the keto form generally predominates