16) Which carbonyl is more susceptible to nucdeophilic addition, that of cyclohe

Question

16) Which carbonyl is more susceptible to nucdeophilic addition, that of cyclohexanone or 16) that of hexanal? Provide two reasons for your choice. MULTIPLE CHOICE Choose the one alternative that best completes the statement or answers the question 17) why do aldehydes undergo nucleophilic addition reactions, whereas esters undergo 17) nucleophilic acyl substitution reactions? A) Aldehydes are more sterically hindered than esters. B) The carbonyl carbon of an ester is more electrophilic than that of an aldehyde. C) Once the nucleophile adds to an aldehyde, neither H- nor R- can be eliminated because they are strongly basic. hybridized hindered to eliminate one of the attached groups D) The ester carbonyl carbon is sp3 hybridized while the aldehyde carbonyl carbon is sp2 E) Once the nucleophile adds to an aldehyde, the tetrahedral intermediate is too sterically

Explanation / Answer

16)

Aldehydes are generally more reactive than ketones toward nucleophilic addition due to the following factors:

1) STERIC EFFECT : In ketones,two R groups are attached to both sides of the carbonyl group. Where as, in aldehydes, there is one relatively small hydrogen atom is to one side and , and a larger R group is attached to other side of the carbonyl carbon. Thus, steric hindrance is less in aldehydes than in ketones.

2) ELECTRONIC EFFECT : aldehydes have only one alkyl (R) group to donate electron to partially positive carbonyl carbon, where as ketones have two electron?donating alkyl (R) groups. So, in ketones, there is greater amount of electrons being supplied to the carbonyl carbon, thus lesser the partial positive charge on carbonyl carbon and the weaker it will become as a nuclei.

Therefore, from the above points, it is clear that hexanal is more reacttive towards nucleophilic addition than cyclohexanone.

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