1
$\begingroup$

enter image description here

After reading various answers here on StackExchange (like Why is the methyl group electron-donating via the inductive effect? and Strongest negative inductive effect group between trimethylammonium, ammonium and dimethylsulfonium groups), I am repeatedly seeing that -CH3 is electron donating through hyperconjugation. Otherwise is is electron withdrawing. So when comparing the acidic nature of the above two compounds, should we use electron withdrawing or electron donating nature of the methyl group?

Also will there be a difference if there is a normal cyclohexane instead of the conjugated benzene.

$\endgroup$
5
  • $\begingroup$ yes there will be a difference,when it's benzene due to orthoeffect 2-methylbenzoic acid will be more acidic than benzoic acid,but in case of cyclohexane as methyl is electron donating droup it's acidic nature will be less than unsubstituted one. $\endgroup$ May 12 '20 at 10:49
  • $\begingroup$ but I read here: chemistry.stackexchange.com/questions/65106/… that it is necessary for the neighbouring atom to have an empty p-orbital $\endgroup$ May 12 '20 at 11:05
  • $\begingroup$ as far as i know methyl group is an electron donating group and it is can stabilize by hyper conjugation.But in this case due to bulky nature of methyl group the COOH group adjacent to it will be out of plane.This inhibits the resonance of carboxyl group with phenyl ring which increases the acidity of carboxyl group which was otherwise reduced due to destabilizing cross conjugation.(this is orthoeffect). $\endgroup$ May 12 '20 at 12:41
  • $\begingroup$ In this question chemistry.stackexchange.com/questions/65106/… which you have posted is not telling anywhere that methyl is an electron withdrawing group. $\endgroup$ May 12 '20 at 12:45
  • $\begingroup$ Ortho effect which states that 'When a group is present ortho to carboxylic acid group in substituted benzoic acid, the steric hindrance forces the carboxyl group to twist out of the plane of the benzene ring. This inhibits the resonance of carboxyl group with phenyl ring which increases the acidity of carboxyl group which was otherwise reduced due to destabilizing cross conjugation' $\endgroup$ May 12 '20 at 12:46