Chapter 21 Notes - CHAPTER 21 Aldehydes and...

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CHAPTER 21 Aldehydes and Ketones-Nucleophilic Addition 21.1 Structural Features of Aldehydes and Ketones The carbonyl bond in aldehydes and ketones is a polar bond. Polarization of the π bond can be represented by the resonance structures for the carbonyl group. As a result of the polar nature of the carbonyl bond, its reaction with an unsymmetrical reagent is such that the electrophilic part bonds to the carbonyl oxygen atom (Lewis base) and the nucleophilic part to the carbonyl carbon atom (Lewis acid). 21.2 Nomenclature Both common names and IUPAC names exist for aldehydes and ketones. A. Common Names: Common names for aldehydes are derived from carboxylic acids. Examples: Common names for ketones are obtained by appending the word “ketone” to the alkyl or aryl group. Examples: Done by Dr. Felix N. Ngassa for Chemistry 242: Organic Chemistry for Life Sciences 2, GVSU, Spring/Summer 2011. 1
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B. IUPAC Nomenclature: For aldehydes, the terminal –e of the parent alkane is changed to –al . If the CHO group is bonded to a chain of carbons, find the longest chain containing the CHO group, and change the –e ending of the parent alkane to the suffix –al . If the CHO group is bonded to a ring, name the ring and add the suffix –carbaldehyde . Number the chain or ring to put the CHO group at C1, but omit this number from the name. For ketones, the terminal –e of the parent alkane is changed to –one . The parent chain is the longest continuous carbon chain containing the carbonyl group. Number the carbon chain to give the carbonyl carbon the lower number. The common names acetophenone and benzophenone are retained by IUPAC. Examples: Done by Dr. Felix N. Ngassa for Chemistry 242: Organic Chemistry for Life Sciences 2, GVSU, Spring/Summer 2011. 2
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Aldehydes and ketones exhibit dipole-dipole interactions because of their polar carbonyl group. Aldehydes and ketones are unable to form intermolecular hydrogen bonding because they have no O-H bond. Therefore, aldehydes and ketones are less polar than alcohols and carboxylic acids. However, aldehydes and ketones can form hydrogen bonds with H 2 O molecules. The polar nature of the carbonyl group makes aldehydes and ketones have higher boiling point than nonpolar compounds of comparable molecular weight. As a result of hydrogen bonds with H 2 O molecules, low molecular weight aldehydes and ketones are more soluble in H 2 O than nonpolar compounds. In general, aldehydes and ketones having ≤ 5 carbons are H 2 O soluble, while those having > 5 carbons are H 2 O insoluble. Examples: Done by Dr. Felix N. Ngassa for Chemistry 242: Organic Chemistry for Life Sciences 2, GVSU, Spring/Summer 2011. 3
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This note was uploaded on 05/25/2011 for the course CHEMISTRY 242 taught by Professor Ngassa during the Spring '11 term at Grand Valley State University.

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Chapter 21 Notes - CHAPTER 21 Aldehydes and...

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