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Chapter 16. Aldehydes & Ketones: Nucleophilic Addition to the Carbonyl Group. About The Authors. These PowerPoint Lecture Slides were created and prepared by Professor William Tam and his wife, Dr. Phillis Chang.
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Chapter 16 Aldehydes & Ketones: Nucleophilic Addition to the Carbonyl Group
About The Authors These PowerPoint Lecture Slides were created and prepared by Professor William Tam and his wife, Dr. Phillis Chang. Professor William Tam received his B.Sc. at the University of Hong Kong in 1990 and his Ph.D. at the University of Toronto (Canada) in 1995. He was an NSERC postdoctoral fellow at the Imperial College (UK) and at Harvard University (USA). He joined the Department of Chemistry at the University of Guelph (Ontario, Canada) in 1998 and is currently a Full Professor and Associate Chair in the department. Professor Tam has received several awards in research and teaching, and according to Essential Science Indicators, he is currently ranked as the Top 1% most cited Chemists worldwide. He has published four books and over 80 scientific papers in top international journals such as J. Am. Chem. Soc., Angew. Chem., Org. Lett., and J. Org. Chem. Dr. Phillis Chang received her B.Sc. at New York University (USA) in 1994, her M.Sc. and Ph.D. in 1997 and 2001 at the University of Guelph (Canada). She lives in Guelph with her husband, William, and their son, Matthew.
Introduction • Carbonyl compounds
Nomenclature of Aldehydes &Ketones • Rules • Aldehyde as parent (suffix) • Ending with “al”; • Ketone as parent (suffix) • Ending with “one” • Number the longest carbon chain containing the carbonyl carbon and starting at the carbonyl carbon
group as a prefix: methanoyl or formyl group • group as a prefix: ethanoylor acetyl group (Ac) • groups as a prefix: alkanoylor acyl groups
Synthesis of Aldehydes 4A. Aldehydes by Oxidation of 1oAlcohols
4C. Aldehydes by Reduction of AcylChlorides, Esters, and Nitriles
LiAlH4 is a very powerful reducing agent, and aldehydes are easily reduced • Usually reduced all the way to the corresponding 1o alcohol • Difficult to stop at the aldehyde stage • Not a good method to synthesize aldehydes using LiAlH4
Two derivatives of aluminum hydride that are less reactive than LAH
Aldehydes from esters and nitriles: RCO2R’RCHO RC≡NRCHO • Both esters and nitriles can be reduced to aldehydes by DIBAL-H
Synthesis of Ketones 5A. Ketones from Alkenes, Arenes,and 2o Alcohols • Ketones (and aldehydes) by ozonolysis of alkenes
Suggest synthesis of from and
5 carbons here 4 carbons here • Retrosynthetic analysis need to add one carbon
disconnection disconnection • Retrosynthetic analysis
Suggest synthesis of from and
5 carbons here 5 carbons here • Retrosynthetic analysis no need to add carbon
disconnection • Retrosynthetic analysis
Nucleophilic Addition to theCarbon–Oxygen Double Bond • Structure Nu⊖ • Carbonyl carbon: sp2 hybridized • Trigonal planar structure
Polarization and resonance structure • Nucleophiles will attack the nucleophilic carbonyl carbon • Note: nucleophiles usually do not attack non-polarized C=C bond
Also would expect nucleophilic addition reactions of carbonyl compounds to be catalyzed by acid (or Lewis acid) • Note: full positive charge on the carbonyl carbon in one of the resonance forms • Nucleophiles readily attack
6A. Reversibility of NucleophilicAdditions to the Carbon–OxygenDouble Bond • Many nucleophilic additions to carbon–oxygen double bonds are reversible; the overall results of these reactions depend, therefore, on the position of an equilibrium
small large • Steric factors
Electronic factors (positive inductive effect from both R & R' groups) carbonyl carbon less d+ (less nucleophilic) (positive inductive effect from only one R group)
The Addition of Alcohols:Hemiacetals and Acetals • Acetal & Ketal Formation: Addition of Alcohols to Aldehydes Catalyzed by acid
