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Q58. Consider the following alcohols The order of decreasing reactivities of these alcohols towards nucleophilic substitution with HBr is A) III > I > IV > II B) III > I > II > IV C) I > III > IV > II D) I > III > II > IV Wait a min ...,., i think im being misled !!! Nuclephilic substitution with HBr ..that means that the compounds present above should be the most electrophilic right??? No??? I thought the ans would be the choice which has p-nitromethylhydroxybenzene on top but i was taken aback by the choices given !!! What is the concept that i must apply over here???? Plzzz help me plzzz.......i wannna crack aieee plzzz............................................. Please help me !!


Q58. Consider the following alcohols The order of decreasing reactivities of these alcohols towards nucleophilic substitution with HBr is










A) III > I > IV > II










B) III > I > II > IV










C) I > III > IV > II










D) I > III > II > IV


Wait a min ...,., i think im being misled !!!Yell 

Nuclephilic substitution with HBr ..that means that the compounds present above should be the most electrophilic right???Undecided No???

I thought the ans would be the choice which has p-nitromethylhydroxybenzene on top but i was taken aback by the choices given !!!Surprised 

What is the concept that i must apply over here????

Plzzz help me plzzz.......i wannna crack aieee plzzz.............................................

Please help me !!

Grade:12

2 Answers

vikas askiitian expert
509 Points
11 years ago

this reaction will peoceed through SN1 path

first step is protonation(H+ from HBr) & formation of O+H2 , this group is highly strong leaving group ...

now , carbocation formation takes place & reactivity is governed on the basis of carbocation stablity ...

most stable III , due to presence ofO-CH3 group , this will disperse +ve charge on carbon ...

then I , coz here no electron withdrawing groups ...

then IV , highly unstable due to EW effect of Br ..

then II , highly unstable coz EW (inductive as well as resonance) effect of NO2

option A) is correct

Gurwinder Kaur
65 Points
11 years ago

option-A is correct...

bcoz -NO2 group increases the acidity of p-nitrobenzylalcohol more than of p-bromobenzylalcohol by -Br group while -OCH3 group decreases the acidity of p-methoxybenzylalcohol than that of benzylalcohol...

decreasing order of acidity is.......-NO2>-Br>-H>-OCH3

therefore,  decreasing order of reactivity is......-OCH3>-H>-Br>-NO2

So, option A is correct....

approve if u like....

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