Complete the reactions with mechanism.

Dinesh khalmaniya 1

The reduction of conjugated carbonyl compounds by NaBH4 gives substantial amount of fully saturated alcohols.Yeah, It can. The reduction of conjugated carbonyl compounds by NaBH4 gives substantial amount of fully saturated alcohols.Oxidation and reduction reactions are the most complex of all reactions in organic chemistry and they are dependent on so many factors. I have tried to keep a balance here between what have been/maybe asked in IIT/AIIMS exam. The results which are not explained here are better understoood by factors related to different solvents and sometimes easily explained by MOT.Generally, neither LiAlH4 nor NaBH4 is able to reduce an isolated C=C But——Cinnamaldehyde, C6H5-CH=CH-CHO when added slowly to an excess of the LiAlH4 dissolved in ether (normal addition), gives C6H5CH2CH2-OHwhereas in “inverse addition method” where LiAlH4/ether is added slowly to Cinnamaldehyde, so that LiAlH4 is never in excess, the product is cinnamyl alcohol, C6H5-CH=CH-CH2OH.The exact process and products of reduction of conjugated carbonyl compounds is dependent on the nature of reductant.In case of conjugated aldehyde or ketone, nucleophilic attack takes place at either the β-carbon (conjugate addition) or at the carbonyl carbon (direct addition).According to the HSAB Principle the vinylic β-carbon is a "soft" electrophilic center and prefer to react with "soft" nucleophiles whereas the carbonyl carbon is a "hard" electrophilic center and hence prefers to react with "hard" nucleophiles.NaBH4 is a rather soft nucleophile and thus it prefers in some cases to react with 4-position or reduces conjugated >C=C< (called 1,4-addition) followed by reduction of aldehyde or ketone into the alcohol by NaBH4 in a second step.The extent of reduction to saturated alcohol is usually greater with NaBH4 than with LiAlH4.