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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 or Aromatic rings Ketones Carbonyl (-C=O) in middle of chain Contains 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 Aldehydes IUPAC Alkanal Carbonyl C = #1 Ketones IUPAC Alkanone Propanone = acetone Carbonyl C = lowest Common Prefixaldehyde # possible Common Alkyl alkyl ketone Multi-functional Group Compounds What 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 Alcohol Alkene Alkyne Alkoxy (ether) Alkyl Halogen oxohydroxyen- (before suffix) yn- (before suffix) alkoxyalkylhalo- Isomerism Aldehydes Ketones Constitutional Skeletal Constitutional Skeletal Positional Functional group Functional group (this is the second time we encounter this type of isomerism) 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 Aldehydes Boiling Point Alkanes<Aldehydes<Alcohols Bonding/polarity Water Solubility Water can H-bond with aldehydes Mass relationship Odors Low MW = unpleasant High MW = fragrant Ketones Boiling Point Same as for Aldehydes Water Solubility Same as for Aldehydes Acetone is infinitely soluble* Odors Pleasant Perfumes & air fresheners Preparation Reactions Aldehydes Ketones Oxidation Oxidation 1˚ alcohol --> aldehyde 2˚ alcohol --> ketone Chemical Reactions - Oxidation Aldehydes Aldehyde --> Carboxylic acid Ketones Ketone --> NR Chemical Reactions - Tollen’s Reagent Aldehydes Ketones RCHO + Ag+ -->RCOOH + Ag(s) RCOR + Ag+ --> NR (a) An aqueous solution of ethanal is added to a solution of silver nitrate. (b) The solution darkens as ethanal is oxidized to ethanoic acid. (c) The inside of the beaker becomes coated with metallic silver. Chemical Reactions - Fehling’s or Benedict’s Reagent Aldehydes Ketones RCHO + Cu2+ --> RCOOH + Cu2O RCOR + Cu2+ --> NR Diabetes test Chemical Reactions - Reduction (Opposite of Oxidation) Aldehydes Ketones RCHO --> 1˚ alcohol RCOR --> 2˚ alcohol Chemical Reactions - Reaction with Alcohol Aldehydes Ketones RCHO + ROH --> Hemiacetal RCOR + ROH --> Hemiacetal (unstable, unless cyclic) Hemiacetal + ROH --> Acetal Hemiacetal + ROH --> Acetal Hydrolysis of acetal produces Hydrolysis of acetal produces the aldehyde + 2 alcohol molecules CH2(OCH3)2 + H2O --> HCHO + 2CH3OH 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