39Nice one subho!
http://www.chemicalforums.com/index.php?topic=42182.msg161571#msg161571 for some more info.
anniline substituted with a methyl group in the ortho position is a weaker base than unsubstituted annilin.... this is given in solomons .... the reason mentioned is ortho effect.
I feel the methyl group in the ortho position in anniline by virtue of it's +i effect will make the lone pair on the nitrogen more easily avaliable foe donation in comparision to anniline.. so should'nt anniline be a weaker base... can u please explain this?
after that they have mentioned anniline substituted with a ch3o group in the para position is a stronger base than the same substituent at ortho position why??
i know this has been discussed before but the previous thread did not end with a concrete answer....
Also with ref to the post http://targetiit.com/iit-jee-forum/posts/organic-doubts-p-8470.html
it has been mentioned that ortho substituted aromatic compounds are always more acidic... is this applicable even if the substituent is a +i effect exerting group...
Pls reply ... i am very confused with this portion ....
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3 Answers
49I will try to share my little knowledge in organic chemistry...if that helps..
whenever there are bulky groups present in ortho positions, there is a lot of steric repulsion from which the molecules want to get rid of..
so what happens is the groups tend to bend away from the plane of the benzene molecule..
this relieves the molecule of the steric strain but the molecule has pay a sum for it..
since the group has bent out of the plane of the benzene molecule, there cannot be any release of electrons by resonance effect..only inductive effects will be in play...
as a result, there is decrease in basicity in o-methyl aniline and marked increase in acidic character in ortho substituted carboxylic acids...!! :)
This gyan is extracted from Organic Chemistry by RobertThornton Morrison and Robert Neilson Boyd.!! :P :P :P
39
6this is wat is called STERIC INHIBITION TO RESONANCE or u can say the SIR effect!!
