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ALDEHYDES & KETONES

ALDEHYDES & KETONES. Melanin - a polymeric substance involving many interconnected cyclic ketone units that colors human hair & skin. 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

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ALDEHYDES & KETONES

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  1. ALDEHYDES & KETONES Melanin - a polymeric substance involving many interconnected cyclic ketone units that colors human hair & skin

  2. 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 Functional Group

  3. Aldehydes and ketones are related to alcohols in a similar manner as alkenes are related to alkanes.

  4. Aldehydes IUPAC Alkanal Carbonyl C = #1 Common Prefixaldehyde Ketones IUPAC Alkanone Propanone = acetone Carbonyl C = lowest # possible Common Alkyl alkyl ketone Nomenclature

  5. 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 oxo- • Alcohol hydroxy- • Alkene en- (before suffix) • Alkyne yn- (before suffix) • Alkoxy (ether) alkoxy- • Alkyl alkyl- • Halogen halo-

  6. Aldehydes Constitutional Skeletal Functional group (this is the second time we encounter this type of isomerism) Ketones Constitutional Skeletal Positional Functional group Isomerism

  7. 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 Common & Naturally Occurring Aldehydes & Ketones

  8. 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 Physical Properties

  9. Aldehydes Oxidation 1˚ alcohol --> aldehyde Ketones Oxidation 2˚ alcohol --> ketone Preparation Reactions

  10. Aldehydes Aldehyde --> Carboxylic acid Ketones Ketone --> NR Chemical Reactions - Oxidation

  11. Aldehydes RCHO + Ag+ -->RCOOH + Ag(s) Ketones RCOR + Ag+ --> NR Chemical Reactions - Tollen’s Reagent (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.

  12. Aldehydes RCHO + Cu2+ --> RCOOH + Cu2O Diabetes test Ketones RCOR + Cu2+ --> NR Chemical Reactions - Fehling’s or Benedict’s Reagent

  13. Aldehydes RCHO --> 1˚ alcohol Ketones RCOR --> 2˚ alcohol Chemical Reactions - Reduction(Opposite of Oxidation)

  14. 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 Chemical Reactions - Reaction with Alcohol

  15. Phenols and formaldehyde react via substitution reactions and polymerize via dehydration reactions. Plastics and adhesives (for plywood) Phenol + Formaldehyde

  16. Sulfur analog of Acetone Penetrates skin very quickly. Anti-inflammatory rub Reduces to dimethyl sulfide in the body. Garlic-like odor DMSO (dimethyl sulfoxide)

  17. 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

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