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CHAPTER 21: ALDEHYDES + KETONES
GENERAL INFO
EXAMPLES OF ALDEHYDES + KETONES
Formaldehyde Preservant
Acetaldehyde Main cause of hangovers
Cinnamaldehyde Taste + odor of cinnamon
Citronellal Mosquito repellant
Acetone Solvent, some nail polish
removers
Butanedione (Diacetyl)
Artificial butter flavor
Dihydroxy acetone Sunless tanner
“Ketone bodies” Formed with a low carb diet
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NOMENCLATURE 1. Aldehydes: the C=O is understood to be carbon #1. Ending is –al.
2. Ketones are named by IUPAC and a common naming system: Common system: order alkyl groups alphabetically. “Alkyl alkyl ketone” IUPAC: Ending is –one.
Common name:
IUPAC name:
3. Multiple Functional Groups: the higher priority group is the “parent” and others are substituents.
4. With alkenes/ alkynes they become: –enal, –ynal, –enone, and –ynone.
Priorities (high to low): Carboxylic acid
Aldehydes Ketones Alcohols Amines
Alkene/Alkyne Ether
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SPECTROSCOPY
1H NMR SPECTRA
13C NMR SPECTRA
b
c
a Zoom-in of b
Carbon of carbonyl
Ald/Ket:185-220 ppm
Ester/Acid/Amide155-185 ppm
O
O
HO
O
H
O
OCH3
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IR SPECTRA
IR Wavenumbers1
WITTIG REACTION
GENERAL REACTION
“ylide” or “ylid” are when a cation and anion are next to each other, with octets on both.
1 Jones, M., Fleming, S.A., Organic Chemistry, 4th ed., Norton, 2010, pp. 830.
Georg Wittig, (German), published this rxn in 1954
Nobel Prize in 1979
1723 cm-1
1684 cm-1
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Formation of the ylide:
REACTION MECHANISM
EXAMPLES
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RETROSYNTHESIS
BIOCHEMISTRY APPLICATION
C6H12O6 (glucose) + yeast enzymes à CH3CH2OH (ethanol) + CO2
O
O
O
GlucoseGlycolysis
pyruvate
H
O
acetaldehyde
OH
ethanol
O
O
O S
NCH3
OPP
N
NH2N
CH3
thiamin diphosphate ylide (TPP ylide)
S
N
R
CH3
R'
OH
OO
S
N
R
CH3
R'
OH
H
O
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HYDRATION
GENERAL REACTION
MECHANISMS
IN TRACE BASE
IN TRACE ACID
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DEGREE OF REACTION
EQUILIBRIUM CONSTANTS
K 2 1.2 × 10–7 0.0014 0.23 1.06
K 37 2.28 × 103 2.8 × 104 1.2 × 106
2 Some K’s from: Jones, M., Fleming, S.A., Organic Chemistry, 4th ed., Norton, 2010, pp. 839. Others from: Carey, F.A., Sundberg, R.J., Advanced Organic Chemistry A, 4th ed., Kluwer Academic/Plenum Publishing, 2000, pp. 450.
R R
O
R R
HO OHH2O K = [hydrate] [carbonyl]tr. H+
H
O
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EXPLANATION: ALDEHYDE VS. KETONE
EXPLANATION: ALDEHYDE VS. ALDEHYDE WITH EWG
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PROBLEMS 1. Both aldehydes are in equilibrium with their hydrate form. Which compound should have a higher
percentage of hydrate?
2. Which compound has a higher Keq for hydrate formation?
REVIEW OF CHROMIUM OXIDATIONS
H
O
HO
H
O
O2N R H
O
R H
HO OHH2O
Keq
OHCrO3H2SO4
OHPCC
CH2Cl2 H
O
OH
O
OCr
OH
O OH H
O
H
OH
HH2O
OH
OCr
OH
O OHO H
O
OH
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ACETALS
ACETAL FORMATION REACTION
ACETAL FORMATION MECHANISM
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EXAMPLES
APPLICATION: CARBOHYDRATES
Cellulose Chitin
Cotton is 90% cellulose
Chitin is the hard exoskeleton of many animals
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ACETAL HYDROLYSIS REACTION
ACETAL HYDROLYSIS MECHANISM
EXAMPLES
For the reaction in the box, is A or B the second step in the mechanism?
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APPLICATION: VANILLA
ACETAL PROTECTING GROUPS
SITUATION
SOLUTION
H
O
O OOH
OH
OH
HO
OCH3
Enzymatic hydrolysis
O
Bra. Mg
b.H
O
CH3c. H+
a. Mg
b.H
O
CH3c. H+
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IMINES + ENAMINES
IMINE / ENAMINE FORMATION REACTIONS Reaction of aldehyde or ketone:
IMINE FORMATION MECHANISM (HYDROLYSIS IS BACKWARDS)
PARTIAL ENAMINE FORMATION MECHANISM
CH3NH2tr. H+
O
H
(CH3)2NH
tr. H+
O
H
OCH3NH2
tr. H+
O(CH3)2NH
tr. H+
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EXAMPLES
APPLICATION: ENZYMATIC ATTACHMENTS
NH2H
O
pH 5-6
NH
O
tr. H+
2,4-dinitrophenylhydrazine (2,4-DNPH)
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HYDROLYSIS REACTIONS
EXAMPLES
APPLICATION: AMINO ACID METABOLISM
H
NH3C
H+, H2O
H
NH3C
H+, H2OCH3
O
OH3N
R
generic amino acid
metabolismO
OH3N
glutamate
NAD+O
ON
H
HH2O
OO OO
