The reduction of ketones and aldehydes to yield alcohols is an example of a nucleophilic addition reaction. Having a hydrogen behave as a nucleophile may seem strange, at first because we have generally referred to its use in acids behaving as an elecotrophilic species, H + . Hydrides, H – , as nucleophiles are widely used in small scale reactions in a laboratory setting. The exact details of carbonyl-group reduction by hydride agents (LiAlH4 and NaBH4) are complex because there is no such species as a discrete H – . We treat these metal hydrides as if they were Hydride ion equivalents and the fundamental step in carbonyl-group reduction is a nucleophilic addition. Read page 432-433 in 5th edition of Wade, Organic Chemistry text. All four hydrogens atoms attached to boron may be transferred in this way to produce the intermediate borate salt which is decomposed upon addition of water and acid to yield the alcohol. PRE-LAB EXERCISE:
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