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ALDEHYDES & KETONES
Melanin - a polymeric substance involving many interconnected cyclic ketone units that colors human hair & skin
Functional Group Aldehydes
Carbonyl (-C=O) at end of chain
Contains a polar bond
RCHO Aliphatic chains NOT as part of ...
Aliphatic rings orAromatic rings
Ketones Carbonyl (-C=O) in
middle of chainContains a polar bond
RCOR Aliphatic chains Aliphatic rings NOT as part of
Aromatic rings
Aldehydes and ketones are related to alcohols in a similar manner as alkenes are related to alkanes.
Nomenclature
AldehydesIUPAC
AlkanalCarbonyl C = #1
CommonPrefixaldehyde
KetonesIUPAC
AlkanonePropanone =
acetone
Carbonyl C = lowest # possible
CommonAlkyl alkyl ketone
Multi-functional Group CompoundsWhat name do you use when there is
more than one functional group?
To determine which suffix to use, follow this priority list (high to low):
Substituent name
Aldehyde Ketone oxo- Alcohol hydroxy- Alkene en- (before suffix) Alkyne yn- (before suffix) Alkoxy (ether) alkoxy- Alkyl alkyl- Halogen halo-
Isomerism
AldehydesConstitutional
Skeletal
Functional group (this is the second time we encounter this type of isomerism)
KetonesConstitutional
SkeletalPositional
Functional group
Common & Naturally Occurring Aldehydes & Ketones
Aldehydes Formaldehyde
methanal Acetaldehyde
ethanal Odors/Flavors
Vanillin Benzaldehyde --> Cinnamaldehyde Lots of nuts & spices
Ketones Acetone
propanone Odors/Flavors
Cloves (2-heptanone) Lots of nuts & spices Butter (butanedione) Fresh-mown hay (coumarin)
Steroid Hormones Testosterone Progesterone Cortisone
Physical Properties
AldehydesBoiling Point
Alkanes<Aldehydes<Alcohols
Bonding/polarity
Water Solubility Water can H-bond with aldehydes Mass relationship
Odors Low MW = unpleasant High MW = fragrant
KetonesBoiling Point
Same as for Aldehydes
Water Solubility Same as for Aldehydes Acetone is infinitely soluble*
Odors Pleasant
Perfumes & air fresheners
Preparation Reactions
AldehydesOxidation
1˚ alcohol --> aldehyde
KetonesOxidation
2˚ alcohol --> ketone
Chemical Reactions - Oxidation
Aldehydes Aldehyde --> Carboxylic
acid
Ketones Ketone --> NR
Chemical Reactions - Tollen’s Reagent
Aldehydes
RCHO + Ag+ -->RCOOH + Ag(s)
Ketones
RCOR + Ag+ --> NR
(c) The inside of the beaker becomes coated with metallic silver.
(b) The solution darkens as ethanal is oxidized to ethanoic acid.
(a) An aqueous solution of ethanal is added to a solution of silver nitrate.
Chemical Reactions - Fehling’s or Benedict’s Reagent
Aldehydes
RCHO + Cu2+ --> RCOOH + Cu2O
Diabetes test
Ketones
RCOR + Cu2+ --> NR
Chemical Reactions - Reduction
(Opposite of Oxidation)Aldehydes
RCHO --> 1˚ alcohol
Ketones
RCOR --> 2˚ alcohol
Chemical Reactions - Reaction with Alcohol
Aldehydes
RCHO + ROH --> Hemiacetal (unstable, unless cyclic)
Hemiacetal + ROH --> Acetal
Hydrolysis of acetal produces the aldehyde + 2 alcohol molecules CH2(OCH3)2 + H2O --> HCHO +
2CH3OH
Ketones
RCOR + ROH --> Hemiacetal
Hemiacetal + ROH --> Acetal
Hydrolysis of acetal produces the ketone + 2 alcohol molecules
Phenol + Formaldehyde
Phenols and formaldehyde react via substitution reactions and polymerize via dehydration reactions.
Plastics and adhesives (for plywood)
DMSO (dimethyl sulfoxide)
Sulfur analog of Acetone
Penetrates skin very quickly. Anti-inflammatory rub
Reduces to dimethyl sulfide in the body. Garlic-like odor
What do you need to know? Structural characteristics (know the functional group)
Aldehydes Ketones Acetals Isomers
Nomenclature (the rules for naming the molecules) Common & IUPAC
Physical properties (basic/simple) BP; Solubility; Flammability
Occurrence and uses (common) Natural (ex.: nuts & spices,melted butter odor, melanin ) Synthetic (ex.: formalin, Bakelite)
Preparation (what basic reactions produce the molecules) Aldehydes - oxidation of 1˚ alcohols Ketones - oxidation of 2˚ alcohols
Characteristic reactions of the molecules Oxidation-reduction Fehling’s & Tollens’ reactions rxn w/ alcohols