Asked in UHS MDCAT 2019 2019Moderate

Which derivative of benzene shows maximum reactivity in electrophilic substitution reactions?

Correct answer: B. Methyl benzene

  • A. Benzoic acid
  • B. Methyl benzene
  • C. Benzaldehyde
  • D. Nitrobenzene

Explanation

Activating groups increase the reactivity of electrophilic substitutions, whereas deactivating groups decrease it.Activating groups are (from most activating to least): -NH2, -NR2 > -OH, -OR> -NHCOR> -CH3 and other alkyl groups, where R is an alkyl group.Deactivating groups are (from most deactivating to least): -NO2, -CF3> -COR (COR can be both carboxylic acids or aldehydes), -CN, -CO2R, -SO3H > Halogens.Among the options, only B describes benzene with an activating group so, it is correct. All other options describe deactivating groups as one can see from the lists mentioned.

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About Benzene and Aromatic Compounds

Benzene has a planar ring of delocalised π electrons, giving aromatic stability and equal carbon-carbon bond lengths. The topic covers resonance, electrophilic substitution reactions such as nitration, halogenation, sulphonation and Friedel-Crafts reactions, along with substituent effects and the distinction between substitution in benzene and addition in ordinary alkenes.

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