The increasing order of the reactivity of the following compounds towards electrophilic aromatic substitution reaction is: (A) (III) < (I) < (II) (B) (III) < (II) < (I)
(C) (II) < (I) < (III) (D) (I) < (III) < (II)
Answers
Answer:
a and b one of this is correct here
The increasing order of reactivity of the given compounds towards electrophilic aromatic substitution is : (A) (III) < (I) < (II)
• The reactivity of an aromatic compound towards electrophilic substitution depends upon the substitutent or functional group attached to the aromatic ring.
• The more electron donating the substitutent is, the more is the activation of the compound towards electrophilic aromatic substitution.
• Here, the first compound (compound I) is chlorobenzene, having the halogen Cl as the substitutent.
• A halogen is an electron withdrawing group due to -I or negative inductive effect.
• It pulls the electrons towards itself, thereby decreasing the electron density on the benzene ring and slowing down its rate towards electrophilic substitution.
• Compound II, toluene, has a methyl group attached to the benzene ring, which is highly electron donating in nature with a +I or positive inductive effect.
• The -CH₃ group, therefore, increases the electron density on the benzene ring, making it highly activating towards electrophilic aromatic substitution.
• Compound III, acetophenone, has a carbonyl group (COCH₃) attached to the benzene ring, which is even more deactivating than the chlorine atom.
• Therefore, -COCH₃ has the highest -I effect and is the most deactivating among the given substituents.
• Therefore, the order of electrophilic aromatic substitution starting from least to highest is :
(III) < (I) < (II), which matches with option (A).