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Last one is more acidic than other but it shows + i effect, so how it becomes more acidic?
last one is more acidic than other but it shows + i effect, so how it becomes more acidic?
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Priyanshu kumar
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Even though the tert-butyl group has greater +I effect, one needs to remember that these alkyl groups have hyperconjugable hygrogen atoms. The electron donating effect through hyperconjugation is greater than that through inductive effect. Now, for hyperconjugation to occur, the atoms need to be in the same plane. The tert-butyl group is very bulky and if it remains in the same plane as the benzene ring, it suffers huge steric repulsion between the ortho H-atoms and those of the butyl group. Hence, the tert-butyl group prefers to be out of plane from the benzene nucleus which greatly diminishes the extent of hyperconjugation. Hence, methyl group which is less bulky donates electron density to a much greater extent than tert-butyl group which decreases the acidity of the phenol derivative.
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The hyperconjugative effect tert butyl group is least With increase in +H effect acidity decreases and vice versa...So para tert butyl phenol is most acidic among all.Also you know hyperconjugative effect is dominating over inductive effect see this
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so rather than tert butyl group has more +I effect among all...should have least acidity but due to least dominating hyperconjugative effect here situation changes
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Dinesh khalmaniya 1 Best Answer
first three show +H effect and +H effect decrease from I>II>III and last one i.e., show only +I effect because it's doesn't have any alpha H. we know that Hyperconjugation is dominant over inductive effect. so there are EDG so decrease the acidity but +H is dominant so it decrease more acidity as compair to +I effect. Overall acidiy = IV> III>II>I
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