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ALDEHYDES AND KETONES I. NUCLEOPHILIC ADDITION TO CARBONYL

ALDEHYDES AND KETONES I. NUCLEOPHILIC ADDITION TO CARBONYL. Chapter 16. Reading Assignment. DO: Sections 16.0 through 16.7 SKIP: Section 16.8 DO: 16.9 through 16.18 SKIP: Section 16.19 DO: Section 16.20 Organic Nomenclature: Aldehydes and Ketones. Problem Assignment.

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ALDEHYDES AND KETONES I. NUCLEOPHILIC ADDITION TO CARBONYL

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  1. ALDEHYDES AND KETONES I.NUCLEOPHILIC ADDITION TO CARBONYL Chapter 16 WWU Chemistry

  2. Reading Assignment • DO: Sections 16.0 through 16.7 • SKIP: Section 16.8 • DO: 16.9 through 16.18 • SKIP: Section 16.19 • DO: Section 16.20 • Organic Nomenclature: Aldehydes and Ketones WWU Chemistry

  3. Problem Assignment • In-Text Problems • 16.1 through 16.27 • End-of-Chapter • 1 through 6 • 7a; 7c through 7j • 8 b, c, d • 9 through 10 • 12 through 14 WWU Chemistry

  4. Aldehyde Ketone WWU Chemistry

  5. IUPAC Nomenclature of Ketones • Choose the longest continuous carbon chain that contains the carbonyl carbon • Number from the end of the chain closest to the carbonyl carbon • Ending is -one • Do the ketonessection of Organic Nomenclature -- Assignment! WWU Chemistry

  6. Example 2-Pentanone WWU Chemistry

  7. Another... 4-Ethyl-3-hexanone WWU Chemistry

  8. And another... 3-Isopropylcyclopentanone or 3-(1-Methylethyl)cyclopentanone WWU Chemistry

  9. Common, or Trivial, Names • Name each group attached to the carbonyl group as an alkyl group • Combine into a name, according to: • alkyl alkyl’ ketone • NOTE: This is not all one word! WWU Chemistry

  10. Example of a Common Name Methyl propyl ketone WWU Chemistry

  11. Another example... Diethyl ketone WWU Chemistry

  12. Important example! Dimethyl ketone Acetone WWU Chemistry

  13. Another Important Common Name Acetophenone (Methyl phenyl ketone) WWU Chemistry

  14. IUPAC Nomenclature of Aldehydes • Choose the longest continuous carbon chain that contains the carbonyl carbon • Number from the end of the chain closest to the carbonyl carbon (this will automatically be carbon #1!) • Ending is -al • Note: The carbonyl carbon is not identified by number in the final name. • Do the aldehydessection of Organic Nomenclature -- Assignment! WWU Chemistry

  15. Example Hexanal Notice that there is no “-1-” in the name! WWU Chemistry

  16. … another: 5-Methylhexanal WWU Chemistry

  17. One more: 3-Phenylpropanal WWU Chemistry

  18. For cyclic molecules, the ending is -carbaldehyde Cycloheptanecarbaldehyde WWU Chemistry

  19. Two acceptable alternative names: Benzenecarbaldehyde (official IUPAC name) Benzaldehyde (acceptable IUPAC name) WWU Chemistry

  20. Common Names of the Aldehydes WWU Chemistry

  21. Forming Common Names of Aldehydes WWU Chemistry

  22. Also: “Iso” names: • Whenever there is a -CH(CH3)2 group, an alternative common name is an “iso” name. • The “iso” name includes all of the carbon atoms in the molecule. • The “iso” name isn’t used if there are other substituents. WWU Chemistry

  23. Example b-Methylbutyraldehyde Isovaleraldehyde WWU Chemistry

  24. Another example... e-Bromocaproaldehyde w-Bromocaproaldehyde WWU Chemistry

  25. Benzaldehyde ortho (o-) meta (m-) para (p-) 1,2- 1,3- 1,4- WWU Chemistry

  26. More than one subsituent: 4-Hydroxybutanal g-Hydroxybutyraldehyde The prefix for -OH is hydroxy WWU Chemistry

  27. Also... 2-Methoxypentanal a-Methoxyvaleraldehyde WWU Chemistry

  28. Bourgeonal is thought to be a chemoattractant emitted by the egg and detected by an odor receptor on the sperm cell. This guides the sperm to the egg Science, 299, 2054 (2003) WWU Chemistry

  29. Structure of the Carbonyl Group • Hybridization of the carbonyl carbon is sp2. • Geometry of the carbonyl carbon is trigonal planar • Attack by nucleophiles will occur with equal ease from either the top or the bottom of the carbonyl group. • Hybridization of the oxygen is “nominally” sp2. WWU Chemistry

  30. Prochiral The carbonyl carbon is prochiral. That is, the carbonyl carbon is not the center of chirality, but it becomes chiral as the reaction proceeds. These two products are enantiomers. In general, both enantiomers are formed in equal amount. WWU Chemistry

  31. Reaction of the Carbonyl Group with Acids Typical behavior WWU Chemistry

  32. Reaction of the Carbonyl Group with Bases Typical behavior WWU Chemistry

  33. Nucleophilic Addition to Carbonyl -- General Mechanism NOTE: Reversible reaction WWU Chemistry

  34. Nucleophilic Addition to Carbonyl -- in Acid (General Mechanism) NOTE: Reversible reaction WWU Chemistry

  35. The carbocation intermediate has resonance. The positive charge character on carbon makes this an excellent site for attack by Lewis bases (nucleophiles). WWU Chemistry

  36. Once we have the intermediate, what happens to it? Case 1: The Addition Product is Stable. The reaction stops here. This happens most often when the nucleophilic atom is carbon, oxygen, or sulfur. WWU Chemistry

  37. Case 2: Addition-Elimination The addition product is unstable with respect to loss of a molecule of water. This is observed most often when the nucleophilic atom is nitrogen or phosphorus. WWU Chemistry

  38. Case 3: Loss of Leaving Group This process is observed when X is a potential leaving group. In this case we have nucleophilic acyl substitution (see Chapter 19). WWU Chemistry

  39. What are the stereochemical requirements? • The hybridization of carbon in the carbonyl group issp2 • The geometry around carbon is trigonal-planar. • Nucleophile can attack the carbonyl group equally easily from top or bottom (see model) • BUT: aldehydes react faster than ketones in nucleophilic addition! WWU Chemistry

  40. Why? • Aldehydes have a hydrogen attached to the carbonyl group, whereas ketones have an alkyl group. • Alkyl groups are much more bulky than hydrogens -- hence ketones should show some steric hindrance. • Alkyl groups have a small electron-releasing inductive effect. • This should make the carbonyl carbon less favorable by attack by nucleophile. • The answer is that there is a combination of steric hindrance and inductive effects that makes ketones react slower than aldehydes. WWU Chemistry

  41. Addition of Cyanide (16.6) A cyanohydrin WWU Chemistry

  42. Mechanism WWU Chemistry

  43. Example • Notice that the cyanide ion and the acid are added in two separate steps! • Sodium carbonate is used to keep the reaction medium basic. WWU Chemistry

  44. So, what’s it good for? Nitriles can be hydrolyzed to form carboxylic acids. This affords us with an important method of synthesizing a-hydroxy-carboxylic acids -- important intermediates in biochemical processes. WWU Chemistry

  45. Reaction with Organometallic Compounds (16.7) The products of this sequence are always alcohols. WWU Chemistry

  46. Addition of Organometallic Reagents The products of the addition are always alcohols. WWU Chemistry

  47. Crude outline of the mechanism of organometallic addition WWU Chemistry

  48. Whatever is attached to the carbonyl group will be attached to the resulting alcohol carbon. WWU Chemistry

  49. Example Organometallics react with ketones to yield tertiary alcohols. WWU Chemistry

  50. And another... Organometallics react with aldehydes to form secondary alcohols WWU Chemistry

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