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Organic Chemistry

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4 Jul 2008 23:33:19 IST

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acid chloride not reduced by diborane?

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Dear sir

i have following doubts

1. why acid chlorides are not reduced by diborane while carboxylic acids can be reduced.

2. why alpha hydroxy ketones give tollen's test.

3. Nucleophilic substitution on ester are easy with respect to carboxylic acid while alkoxide ion is a poor leaving group than hydroxide ion.

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Madhusudan Chavan

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Joined: 9 Mar 2007

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5 Jul 2008 21:26:44 IST

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Hydroxy acetone reduces ammoniacal silver nitrate ( Tollen's reagent), thereby being oxidised to DL- lactic acid. Althogh ketones do not normally reduce Tollen's reagent or Fehling's solution, alpha hydroxy ketones are exceptions. Similarly, ketones form phenyl hydrazone with phenyl hydrazine, but alpha hydroxy ketones form osazones. This is because alpha hydroxy ketone appears to exist as an equilibrium mixture of hydroxy ketone and cyclic hemiacetal forms ( ring-chain tautomerism ).

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