which phenol is the most acidic?


phenol
2-methyl-6-nitrophenol
3-methyl-5-nitrophenol
2,6-dimethyl-3-nitrophenol
2,4,6-trimethylphenol

To determine which phenol is the most acidic, we need to compare their acidity constants or pKa values. The lower the pKa value, the stronger the acid.

One way to estimate the acidity is to consider the electron-withdrawing or electron-donating groups attached to the phenol ring. Electron-withdrawing groups increase the acidity by stabilizing the conjugate base, while electron-donating groups decrease the acidity.

Let's analyze each of the given phenols and compare their characteristics:

Phenol:
Phenol has no additional functional groups attached to the phenol ring. It is less acidic compared to the other compounds because it lacks any substituents that can withdraw electron density from the hydroxyl group. However, it is still acidic due to resonance stabilization of the conjugate base.

2-Methyl-6-nitrophenol:
This compound has a nitro group (–NO2) as a substituent on the phenol ring. Nitro groups are electron-withdrawing due to their strong electron-withdrawing ability. The presence of the nitro group increases the acidity of the phenol by further destabilizing the phenoxide ion. Hence, it is more acidic than phenol.

3-Methyl-5-nitrophenol:
Similar to the previous compound, this phenol also has a nitro group as a substituent. However, in this case, the position of the methyl group is different. The position of substitution does not affect the acidity significantly in this case. Therefore, based on the nitro group, its acidity should be similar to 2-methyl-6-nitrophenol.

2,6-Dimethyl-3-nitrophenol:
This phenol has two methyl groups and a nitro group as substituents on the phenol ring. The presence of two methyl groups in this compound does not significantly affect its acidity as they are electron-donating groups. However, the nitro group still acts as an electron-withdrawing group. The compound is less acidic compared to phenol but more acidic than 2-methyl-6-nitrophenol and 3-methyl-5-nitrophenol.

2,4,6-Trimethylphenol:
This compound has three methyl groups attached to the phenol ring. Methyl groups are electron-donating groups, so they decrease the acidity of phenol. This compound is the least acidic among the given options because it has no electron-withdrawing groups.

Therefore, based on the analysis, the order of acidity for the given phenols is:

2-methyl-6-nitrophenol > 3-methyl-5-nitrophenol > 2,6-dimethyl-3-nitrophenol > phenol > 2,4,6-trimethylphenol