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Chapter 17 Aldehydes and Ketones

Chapter 17 Aldehydes and Ketones. 17.1 Nomenclature. O. O. H. H. O. O. HCCHCH. Nomenclature of Aldehydes. 4,4-dimethylpent anal. 5-hex enal. 2-phenylprop anedial. O. C. H. Nomenclature of Aldehydes. when named as a suffix. when named as a substituent. formyl group.

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Chapter 17 Aldehydes and Ketones

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  1. Chapter 17Aldehydes and Ketones

  2. 17.1Nomenclature

  3. O O H H O O HCCHCH Nomenclature of Aldehydes 4,4-dimethylpentanal 5-hexenal 2-phenylpropanedial

  4. O C H Nomenclature of Aldehydes when named as a suffix when named as a substituent formyl group carbaldehyde carboxaldehyde

  5. O O CH3CH2CCH2CH2CH3 CH3CHCH2CCH3 CH3 H3C O Substitutive Nomenclature of Ketones 3-hexanone 4-methyl-2-pentanone 4-methylcyclohexanone

  6. O O CH3CH2CCH2CH2CH3 CH2CCH2CH3 O H2C CH CHC CH2 Functional Class Nomenclature of Ketones ethylpropyl ketone benzylethyl ketone divinyl ketone

  7. 17.2Structure and Bonding:The Carbonyl Group

  8. Structure of Formaldehyde planar bond angles: close to 120° C=O bond distance: 122 pm

  9. The Carbonyl Group very polar double bond O 1-butene propanal dipole moment = 2.5D dipole moment = 0.3D

  10. O H O Carbonyl group of a ketone is morestable than that of an aldehyde Alkyl groups stabilize carbonyl groups the sameway they stabilize carbon-carbon double bonds,carbocations, and free radicals. heat of combustion 2475 kJ/mol 2442 kJ/mol

  11. O H O Spread is greater foraldehydes andketones than for alkenes Heats of combustion ofC4H8 isomeric alkenes CH3CH2CH=CH2 2717 kJ/mol cis-CH3CH=CHCH3 2710 kJ/mol trans-CH3CH=CHCH3 2707 kJ/mol (CH3)2C=CH2 2700 kJ/mol 2475 kJ/mol 2442 kJ/mol

  12. •• – •• O O •• •• •• C C + Resonance Description ofCarbonyl Group nucleophiles attack carbon; electrophiles attack oxygen

  13. Bonding in Formaldehyde Carbon and oxygen are sp2 hybridized

  14. Bonding in Formaldehyde The half-filledp orbitals oncarbon andoxygen overlapto form a p bond

  15. 17.3Physical Properties

  16. O OH Aldehydes and ketones have higher boilingthan alkenes, but lower boiling points than alcohols. boiling point More polar than alkenes, but cannot form intermolecular hydrogen bonds to other carbonyl groups –6°C 49°C 97°C

  17. 17.4Sources of Aldehydes and Ketones

  18. O Many aldehydes and ketones occur naturally 2-heptanone(component of alarm pheromone of bees)

  19. Many aldehydes and ketones occur naturally O H trans-2-hexenal (alarm pheromone of myrmicine ant)

  20. Many aldehydes and ketones occur naturally O H citral (from lemon grass oil)

  21. Synthesis of Aldehydes and Ketones from alkenes ozonolysis from alkynes hydration (via enol) from arenes Friedel-Crafts acylation from alcohols oxidation A number of reactions alreadystudied provideefficient syntheticroutes to aldehydes and ketones.

  22. O O C C R H R OH What about..? aldehydes from carboxylic acids

  23. O O C C R H R OH What about..? aldehydes from carboxylic acids 1. LiAlH4 PDC, CH2Cl2 2. H2O RCH2OH

  24. O O COH CH CH2OH Example benzaldehyde from benzoic acid 1. LiAlH4 PDCCH2Cl2 2. H2O (83%) (81%)

  25. O O C C R R' R H What about..? ketones from aldehydes

  26. O O C C R R' R H What about..? ketones from aldehydes 1. R'MgX OH PDC, CH2Cl2 2. H3O+ RCHR'

  27. O CH3CH2C(CH2)3 CH3 OH CH3CH2CH(CH2)3 CH3 Example 3-heptanone from propanal O C CH3CH2 H (57%) 1. CH3(CH2)3MgX H2CrO4 2. H3O+

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