chapter19.ppt - Aldehydes and Ketones Aldehydes(RCHO and ketones(R2CO are characterized by the carbonyl functional group(C=O The compounds occur widely

chapter19.ppt - Aldehydes and Ketones Aldehydes(RCHO and...

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Aldehydes (RCHO) and ketones (R 2 CO) are characterized by the carbonyl functional group (C=O) The compounds occur widely in nature as intermediates in metabolism and biosynthesis Aldehydes and Ketones
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Much of organic chemistry involves the chemistry of carbonyl compounds Aldehydes/ketones are intermediates in synthesis of pharmaceutical agents, biological pathways, numerous industrial processes An understanding of their properties is essential Why this Chapter?
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19.1 Naming Aldehydes and Ketones Aldehydes are named by replacing the terminal –e of the corresponding alkane name with –al The parent chain must contain the –CHO group The –CHO carbon is numbered as C1 If the –CHO group is attached to a ring, use the suffix carbaldehyde
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Replace the terminal - e of the alkane name with – one Parent chain is the longest one that contains the ketone group Numbering begins at the end nearer the carbonyl carbon Naming Ketones
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IUPAC retains well-used but unsystematic names for a few ketones Ketones with Common Names
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The R–C=O as a substituent is an acyl group, used with the suffix -yl from the root of the carboxylic acid CH 3 CO: acetyl; CHO: formyl; C 6 H 5 CO: benzoyl The prefix oxo - is used if other functional groups are present and the doubly bonded oxygen is labeled as a substituent on a parent chain Ketones and Aldehydes as Substituents
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Preparing Aldehydes Oxidize primary alcohols using pyridinium chlorochromate Alkenes with a vinylic hydrogen can undergo oxidative cleavage when treated with ozone, yielding aldehydes Reduce an ester with diisobutylaluminum hydride (DIBAH) 19.2 Preparing Aldehydes and Ketones
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Oxidize a 2° alcohol Many reagents possible: choose for the specific situation (scale, cost, and acid/base sensitivity) Preparing Ketones
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Ozonolysis of alkenes yields ketones if one of the unsaturated carbon atoms is disubstituted Ketones from Ozonolysis
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Friedel–Crafts acylation of an aromatic ring with an acid chloride in the presence of AlCl 3 catalyst Aryl Ketones by Acylation
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Hydration of terminal alkynes in the presence of Hg 2+ (catalyst: Section 8.4) Methyl Ketones by Hydrating Alkynes
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CrO 3 in aqueous acid oxidizes aldehydes to carboxylic acids efficiently Silver oxide, Ag 2 O, in aqueous ammonia (Tollens’ reagent) oxidizes aldehydes 19.3 Oxidation of Aldehydes and Ketones
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Aldehyde oxidations occur through 1,1-diols (“hydrates”) Reversible addition of water to the carbonyl group Aldehyde hydrate is oxidized to a carboxylic acid by usual reagents for alcohols Hydration of Aldehydes
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Undergo slow cleavage with hot, alkaline KMnO 4 C–C bond next to C=O is broken to give carboxylic acids Reaction is practical for cleaving symmetrical ketones Ketones Oxidize with Difficulty
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