1. Bettelheim, Brown, Campbell and Farrell Chapter 17
Aldehydes and Ketones
Bettelheim, Brown, Campbell and Farrell
Chapter 17

2. Structure Aldehyde: carbonyl group bonded to a hydrogen atom
in methanal, the simplest aldehyde, the carbonyl group is bonded to two hydrogens
in other aldehydes, it is bonded to one hydrogen and one carbon
Ketone: carbonyl group bonded to two carbons

3. Nomenclature IUPAC names for aldehydes
Change suffix -e of the parent alkane to -al
Aldehyde group can only be at end of chain
Aldehyde group always C-1 so we don’t need to number it.
Start counting chain from aldehyde end
Unsaturated aldehydes show the 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

4. Nomenclature
IUPAC system uses common names for some aldehydes, including

5. Nomenclature IUPAC names for ketones
Find longest chain that contains the carbonyl group
Show ketone by changing the -e of the parent alkane -one
Show position of carbonyl group with a number
Number the parent chain from the direction that gives the carbonyl carbon the smaller number
IUPAC uses the common name acetone for 2-propanone

6. Nomenclature
To name an aldehyde or ketone that also contains an -OH or -NH2 group
Number chain to give the carbonyl carbon the lower number
Show an -OH substituent by hydroxy-, and an -NH2 substituent by amino-
Hydroxy and amino substituents are numbered and alphabetized along with other substituents

7. Nomenclature Common names
Aldehyde: Common name of the corresponding carboxylic acid is modified– substitute the word -aldehyde and for the suffix -ic or -oic acid
Ketone: Name each alkyl or aryl group bonded to the carbonyl carbon as a separate word, followed by the word "ketone”

9. Physical Properties
A C=O bond is polar, with oxygen bearing a partial negative charge and carbon bearing a partial positive charge
Aldehydes and ketones are polar molecules

10. Physical Properties
Intermolecular attractions (dipole-dipole) between partial positive and negative charges on different molecules
NO hydrogen bonding is possible between aldehyde or ketone molecules
Lower boiling points than alcohols and carboxylic acids (which can H-bond with each other)
Small aldehydes and ketones are soluble in water (can form H-bonds WITH WATER)

11. Physical Properties ** **

12. Oxidation
Aldehydes are oxidized to carboxylic acids by a variety of oxidizing agents, including potassium dichromate
Liquid aldehydes are sensitive to oxidation by O2 and must be protected from contact with air during storage

13. Oxidation
Ketones are NOT oxidized 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

14. Reduction
C=O 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

15. Reduction
Most common laboratory reagent for the reduction of an aldehyde or ketone is sodium borohydride, NaBH4
Product is an alcohol
NaBH4 does NOT add H atoms to C=C double bond (only to C=O)
H2 does add H atoms to C=C (and to C=O)

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

19. Addition of Alcohols to Carbonyls
Addition of an alcohol to the carbonyl group of an aldehyde or ketone forms a hemiacetal (a half-acetal)
Functional group of a hemiacetal is a carbon bonded to one -OH group and one -OR group
H of the alcohol adds to the carbonyl oxygen and -OR adds to the carbonyl carbon

20. Addition of Alcohols to Carbonyl
Hemiacetals are generally unstable and are only minor components of most equilibrium mixtures
Major exception: When both the carbonyl group and the hydroxyl group are in the same molecule and can form a cyclic hemiacetal with a 5- or 6-member ring
Cyclic hemiacetals predominate

21. Addition of Alcohols
Hemiacetal can react further with a second alcohol to form an acetal plus water
Reaction is acid catalyzed
Functional group of an acetal is a carbon bonded to two -OR groups

22. Addition of Alcohols
All steps in hemiacetal and acetal formation are reversible
Le Chatelier's Principle applies to this equilibrium
Adding a large excess of alcohol or removing water will shift the equilibrium to the right
Adding a large excess of water will shift the equilibrium to the left

23. Keto-Enol Tautomerism
A carbon atom adjacent to a carbonyl group is called an a-carbon
A hydrogen atom bonded to an a-carbon is called an a-hydrogen

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

25. Keto-Enol Tautomerism
Keto form has C=O double bond
Enol form has C=C double bond and –OH

26. Keto-Enol Tautomerism
Draw structural formulas for the two enol forms for each ketone

27. Keto-Enol Tautomerism
Draw structural formulas for the two enol forms for each ketone
For compounds a & b, two possible isomers exist

28. Nucleic Acids

30. Reactions of Aldehydes and Ketones
Oxidation (K2Cr2O7/H2SO4 OR KMnO4)
Aldehyde → Carboxylic acid
Ketone → No Rxn

31. Reactions of Aldehydes and Ketones
Reduction (H2/Ni,Pd, Pt OR NaBH4)
Aldehyde → 1o Alcohol
Ketone → 2o Alcohol
H2 adds to BOTH C=O and C=C bonds
NaBH4 adds ONLY to C=O bonds (NOT C=C)

32. Reactions of Aldehydes and Ketones
Addition of Alcohols
Aldehyde + ROH → Hemiacetal
Hemiacetal + ROH → Acetal
Summary: Aldehyde + 2 ROH → Acetal
Similar reactions with Ketones