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Aldehydes, ketones and optical isomerism GapFill
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The general formula for both aldehydes and ketones is . Aldehydes can be oxidised to by acidified potassium dichromate( ), K2Cr2O7, under gentle heat. During this process, the reaction mixture will turn from to green. Ketones cannot be oxidised, which is exploited in various chemical tests to distinguish between aldehydes and ketones. For example, if an aldehyde is added to reagent and heated, a 'silver mirror' will be formed as ions are reduced to neutral Ag atoms and the aldehyde is oxidised.
The carbon atom of the carbonyl group has a partial positive charge, and nucleophilic is a common class of reactions for aldehydes and ketones. In reactions with aqueous sodium borohydride (NaBH4), followed by dilute acid, the nucleophile will be a hydride ion (H−), and the carbonyl will be reduced to group. When writing equations for such reduction reactions, you can represent the reductant using the symbol . In reactions with potassium cyanide (KCN), followed by dilute acid, a cyanide ion (−CN) will be the nucleophile, and the products will be .
Optical isomerism is a kind of stereoisomerism, and occurs in organic molecules when a carbon atom has four different groups attached to it. These carbons are called centres, or are said to be . An optical isomer cannot be superimposed on its mirror image; together, an optical isomer and its mirror image are known as . One will rotate plane- light in one direction, while the other will rotate it by the same amount in the opposite direction. A mixture with equal amounts of each, a , will not rotate the light as the effects of the two enantiomers will cancel each other out.