(a) Arrange the following compounds in the increasing order of their acid strength:
p-cresol, p-nitrophenol, phenol
(b) Write the mechanism (using curved arrow notation) of the following reaction :
OR
Write the structures of the products when Butan-2-ol reacts with the following :
(a) CrO3
(b) SOCl2
(a) Increasing order of the acid strength of the given compounds
is: p-cresol, <phenol < p-nitrophenol
Explanation: Phenol is a strong acid (has a strong tendency to release proton). Phenols may be considered to be a resonance hybrid of the following structures:
As a result of resonance, the oxygen atom acquires a partial positive charge. This weakens the O—H bond and thus facilitates the release of a proton. Thus, phenol is a strong acid (has a strong tendency to release proton)
Electron-withdrawing group (--NO2) increases the acidic character of phenols. Electron withdrawing group withdraws the electrons, as a result, the electron density of phenol decreases. This weakens the O—H bond and thus the release of proton become easy which makes it more acidic. Hence the nitrophenol is a stronger acid than phenol.
Electron-donating group (CH3) decreases the acidic character of phenols. Electron donating group donate electrons to the phenol, as a result, the electron density of phenol increases. This strengthens the O—H bond and thus the release of proton become difficult which makes it less acidic. Hence the p-cresol (4-methylphenol) is less acidic than phenol and nitrophenol.
Thus, the acid strength of the given compounds is:
p-cresol, <phenol < p-nitrophenol
(b) The mechanism (using curved arrow notation) of the following
reaction:
Transfer of proton from H3O+ to an alkene to form a carbocation (carbon carrying the positive charge)
OR
Structure of Butane-2-ol is 
(a) When Butane-2-ol reacts with CrO3, it forms butanone.
Explanation: As butane-2-ol is a secondary alcohol (OH is attached on second carbon), hence secondary alcohol is easily oxidized in the presence of chromic anhydride (CrO3) to ketones with the same number of carbons.
(b) When Butane-2-ol reacts with SOCl2, it forms chlorobutane.
Explanation: Butane-2-ol reacts with thionyl chloride (SOCl2) to form chlorobutane by the replacement of OH group by Cl atom.