P-cyanophenol>o-cyanophenol>phenol>m-cyanophenol.This is the acidic order

Introduction:
In this question, we are asked to determine whether the CN group on the ortho position of phenol can form hydrogen bonding with the H of the OH group of phenol. We also need to compare the acidic strength of o-cyanophenol, p-cyanophenol, m-cyanophenol, and phenol.

Hydrogen Bonding:
Hydrogen bonding occurs when a hydrogen atom is bonded to an electronegative atom (such as oxygen or nitrogen) and is attracted to another electronegative atom. In phenol, the OH group acts as the hydrogen bond donor, while the CN group can act as the hydrogen bond acceptor.

Ortho-Cyanophenol:
In ortho-cyanophenol, the CN group is positioned on the ortho position, which is adjacent to the OH group. This close proximity allows for the formation of intramolecular hydrogen bonding between the H of the OH group and the CN group. Therefore, ortho-cyanophenol can form hydrogen bonding.

Para-Cyanophenol:
In para-cyanophenol, the CN group is positioned on the para position, which is opposite to the OH group. The distance between the CN group and the OH group is greater compared to ortho-cyanophenol. As a result, the hydrogen bonding between the H of the OH group and the CN group is weakened. However, it is still possible for para-cyanophenol to form hydrogen bonding, although it is less favorable compared to ortho-cyanophenol.

Meta-Cyanophenol:
In meta-cyanophenol, the CN group is positioned on the meta position, which is further away from the OH group. The distance between the CN group and the OH group is significantly greater compared to ortho- and para-cyanophenol. As a result, the hydrogen bonding between the H of the OH group and the CN group is significantly weakened. It is unlikely for meta-cyanophenol to form hydrogen bonding.

Phenol:
In phenol, there is no additional group attached to the benzene ring. The OH group can readily form intermolecular hydrogen bonding with other phenol molecules or other hydrogen bond acceptors. Phenol exhibits the strongest hydrogen bonding among the compounds mentioned.

Order of Acidic Strength:
The strength of an acid is determined by its ability to donate a proton (H+). In general, the strength of an acid increases with increasing stability of its conjugate base. The stability of the conjugate base depends on the electron-donating or electron-withdrawing nature of the substituents on the benzene ring.

The electron-withdrawing nature of the CN group makes the conjugate base of cyanophenols more stable compared to phenol. This stabilization is due to the delocalization of the negative charge through the electron-withdrawing CN group. Among the cyanophenols, the order of acidic strength is as follows:

1. Ortho-cyanophenol (strongest acid)
2. Para-cyanophenol
3. Meta-cyanophenol (weakest acid)
4. Phenol

The ortho-cyanophenol is the strongest acid because the presence of the CN group