              -C-OH           

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R-C-OH R                      RCOOR'     

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       O

                     CH3COOH          C6H5COOH                           COOH 2             C6H2 COOH 4           X,OH,NH2                   CICH2COOH        CH3CH OH COOH            NH2CH2COOH          CH3COCOOH                     