<P> Finally, substituents can have other effects on a reducing agent's reactivity: acetoxy groups hinder the reducing power of NaBH (OAc) not only through steric bulk but also because they are electron - withdrawing . Cyano groups also hinder reducing agents, while electron - donating groups such as alkyl groups can improve them, such as in superhydride (lithium triethylborohydride), which is a strong enough nucleophile to prevent undesired rearrangements during reduction . </P> <P> Because of these substituent effects, NaBH CN is a very poor reducer at moderate pH (> 4), so it prefers reductive amination to carbonyl reduction, as shown below: </P> <P> The relatively weak reducer sodium borohydride is typically used for reducing ketones and aldehydes because unlike lithium aluminum hydride, it tolerates many functional groups (nitro group, nitrile, ester) and can be used with water or ethanol as solvents . Lithium aluminum hydride and other strong reducers such as diisobutylaluminium hydride, L - selectride, diborane, diazene, and aluminum hydride can also reduce aldehydes and ketones, but are disfavored because they are hazardous and violently reactive . However, these compounds are useful for reducing carboxylic acids and esters to alcohols, since sodium borohydride is not powerful enough to do so . </P> <P> The following table illustrates which carbonyl functional groups can be reduced by which reducing agents (some of these reagents vary in efficacy depending on reaction conditions): </P>

Which reagent can be used to reduce the carbonyl in methyl vinyl ketone