AIIMS MBBS> Why the first one is more acidic than the...

Why the first one is more acidic than the second one....

Abhishek Dogra , 5 Years ago

Grade 12

3 Answers

Bhavya

Last Activity: 5 Years ago

Dear Student
-Me is Electron donating group which dec acidic strength.The effect of -Me is prominently observed at o and p positions due to resonance.

Rajdeep

Last Activity: 5 Years ago

HELLO THERE!

The acidic character of a compound is determined by how easily it can donate an H⁺ ion (proton).

Some points to note: CH₃ (methyl) has +I effect (positive inductive effect, i.e., donating electrons). If, electrons are taken away from the benzene ring, (here, by nitrile group CN, as CN shows -Mesomeric effect) then the lone pair electrons of O atom will be engaged in Resonance inside the ring. This will create a positive charge on oxygen, which thus draws electrons from Hydrogen, adjacent to it. Hence, the Hydrogen develops a positive charge and can be easily given off as H⁺.

Now, a difference in acidic character comes when you attach Methyl group in ortho/para position.

Since for having more acidic character, electron density from the ring is to be withdrawn, the compound having CH₃ group in ortho position is less acidic. This is because, +I effect (electron donating effect) of CH₃ is stronger at Ortho-position (due to ortho effect, any factor, -I or +I, is felt the strongest at ortho position). And, as we have already discussed, if electron density is shifted towards ring, acidic character decreases (as to increase acidic character, electron density is to be withdrawn).

Hence, the first structure (methyl group at meta) is more acidic than the second (methyl group at ortho).

THANKS!

chetan jangir

Last Activity: 5 Years ago

The Simple Difference Between these Structures is position of Methyl Group .Also We know Methyl group has +I effect at ortho and and para positions so Acidic Character in this problem can be concluded by Stability of connjugate base .After oh Gives H+ ther is a negative charge On oxygen atom which is incresed by methyl group in 2 structure and no effect by methy in 1 structure So 1 is more stable. Hence more tendency to give h+