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