Question

21. Which of the following is NOT a m-directing substituent when present on the benzene ring

(a)-NHCOCH₃ (b) –NO₂ (c) –N(CH₃)₃⁺ (d)-CN

23. The relationship of propanone and propen-2-ol is called (a) tautomers (b) conformational isomers (c)distereomers (d)resonance structures

24. Which reagent can be used to distinguish an aldehyde and a ketone? (a) Br₂/CCl₄

(b) KMnO₄/OH^- (c) Ag₂O/NH₄OH (d)None of these

25. The proper name for the molecule below is:

(a) 2-chloro-5-aldehydotoluene (b) 6—chloro-3-aldehydotoluene

(c) 3-methyl-4-chloro-benzaldehyde

(d) 4-chloro-3-methylbenzaldehyde

Answer 1

#21. Electron withdrawing groups (EWG's) are known as m-directing groups because they withdraw electron density from ortho and para positions of aromatic ring and only meta position is available for electrophilic substitution, thus EWG's are m-directing and ring deactivating groups .

While on the other hand , electron donating groups (EDG's) are called ortho and para directing groups and ring activating groups as they donate eletron density on ortho and para positions of aromatic ring (benzene) .

Out of given options ;

(-CN) , (-NO2) and (-N(CH3)3^+) are electron withdrawing groups , so are m-directing.

While -NHCOCH3 , is electron donating, hence ortho and para directing.

Thus option (a) -NHCOCH3 , is the correct answer.