p-Nitrophenol is a stronger acid than phenol while p-cresol is a weake...
NO2 is -R group while -CH3 is +I group, so, NO2 decreases charge density on oxygen in order to facilitate release of H+ ion
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p-Nitrophenol is a stronger acid than phenol while p-cresol is a weake...
Explanation:
Both p-nitrophenol and p-cresol are substituted phenols, where a functional group is attached to the benzene ring. In this case, p-nitrophenol has a nitro group (-NO2) attached to the ring, while p-cresol has a methyl group (-CH3) attached.
Effect of the -NO2 group on p-nitrophenol:
The nitro group is an electron-withdrawing group. It has a strong -I (inductive effect) and -M (mesomeric effect) due to the presence of the electronegative nitrogen and oxygen atoms.
The -I effect decreases the electron density on the oxygen atom of the -OH group in p-nitrophenol. This makes it more acidic because the oxygen atom is less able to donate its lone pair of electrons to stabilize the conjugate base. Therefore, p-nitrophenol is a stronger acid compared to phenol.
Effect of the -CH3 group on p-cresol:
The methyl group is an electron-donating group. It has a weak +I (inductive effect) and +M (mesomeric effect) due to the presence of the carbon atom.
The +I effect increases the electron density on the oxygen atom of the -OH group in p-cresol. This makes it less acidic because the oxygen atom is more able to donate its lone pair of electrons to stabilize the conjugate base. Therefore, p-cresol is a weaker acid compared to phenol.
Comparison between p-nitrophenol and p-cresol:
When comparing p-nitrophenol and p-cresol, we can see that the nitro group (-NO2) in p-nitrophenol decreases the electron density on the oxygen atom, making it a stronger acid. On the other hand, the methyl group (-CH3) in p-cresol increases the electron density on the oxygen atom, making it a weaker acid. Therefore, option B is the correct answer.
It is important to note that the electron-donating or electron-withdrawing nature of a substituent affects the acidity of a compound by influencing the stability of the conjugate base. Electron-withdrawing groups stabilize the conjugate base, making the compound more acidic, while electron-donating groups destabilize the conjugate base, making the compound less acidic.