question_answer

Which of the following will undergo benzoin condensation?

A) Furfural           

B)  4-nitrobenzaldehyde

C)  p.NN-dimethylamino benzaldehyde               

D)  All of these

Correct Answer: A

Solution :

 Idea This problem includes conceptual mixing of benzoin condensation and effect of inductive effect on substrate presence of benzoin condensation. To solve such types of questions, students are advised to understand the role of various electrons withdrawing group and electron releasing group on substrate. Benzoin condensation This is a phenomena of self condensation of aromatic aldehyde in presence of KCN. This process produces \[\alpha \] -hydroxy ketone as a final product. Inductive effect There are two kinds of inductive effect + l effect shown by electron donating group and - l effect shown by electron withdrawing group e.g., \[+l\,\text{effect}\xrightarrow{{}}OC{{H}_{3}}\] \[-\,l\,\text{effect}\xrightarrow{{}}N{{O}_{2}}CHO,CN\] etc. Effect of strong electron donating group or strong electron withdrawing group present on substrate of benzoin condensation play an important role in occurrence of reaction. Aromatic aldehydes having either strong electron withdrawing group or electron with drawing group do not give this reaction.    Hence,  only furfural  will  undergo  benzoin condensation. TEST Edge Generally, in JEE Main this type of questions are asked very frequently so students are advised to study the depth of various chemical rearrangement reactions such as pinacol_ pinacolone      rearrangement,      Beckmann rearrangement which may also be asked.