The key difference between alcohols and phenols is that the alcohols are organic compounds containing –OH group as an essential component whereas the phenols are a group of alcohols which contains –OH group and a benzene ring as essential components.
There are aliphatic and aromatic compounds in organic chemistry, which share the same functional groups. But, their properties may differ from each other due to the aromaticity or the aliphatic nature. Alcohols are organic compounds containing –OH groups as the functional group. Phenol is a category of alcohols. Particularly, it contains a –OH group attached to an aromatic ring. Therefore, it has some different properties, unlike most other alcohol compounds.
What are Alcohols?
The characteristic of the alcohol family is the presence of a –OH functional group (hydroxyl group). Normally, this –OH group attaches to an sp3 hybridized carbon. The simplest member of this family is methyl alcohol, which we call methanol. We can classify the alcohols into three groups as primary, secondary and tertiary. Here, this classification depends on the degree of substitution of carbon to which the hydroxyl group directly attaches.
There, if the carbon has only one other carbon attached to it, we name it as a primary carbon and the alcohol is a primary alcohol. Likewise, if the carbon with the hydroxyl group attaches to two other carbons, then that is secondary alcohol and so on. We name alcohols with a suffix –ol according to the IUPAC nomenclature. First, we need to select the longest continuous carbon chain to which the hydroxyl group directly attaches. Then we need to change the name of the corresponding alkane by dropping the final letter e and adding the suffix ol.
Further, alcohols have a higher boiling point than the corresponding hydrocarbons or ethers. The reason is the presence of intermolecular interaction between these molecules through hydrogen bonding. If the R group is small, alcohols are miscible with water. But as the R group is becoming larger, it becomes hydrophobic. Moreover, these molecules are polar. There, the C-O bond and O-H bonds contribute to the polarity of the molecule. The polarization of the O-H bond makes the hydrogen partially positive and explains the acidity of alcohols.
Apart from that, these are weak acids, and the acidity is close to that of water. Because, –OH is a poor leaving group since OH– is a strong base. But, protonation of the alcohol converts the poor leaving group –OH, into a good leaving group (H2O). The carbon, which directly attaches with the –OH group, is partially positive; therefore, it is susceptible to nucleophilic attack. Further, the electron pairs on the oxygen atom make it both basic and nucleophilic.
What are Phenols?
Phenol is an aromatic hydrocarbon and a derivative of benzene. Phenol is a white crystalline solid with molecular formula C6H6OH. It is flammable and has a strong odour. The molecular weight of this molecule is 94 g mol-1. The melting point is 40.5 oC, and the boiling point is 181 oC. Moreover, the density is 1.07 g cm-3.
Hence, in the process of formation, the hydrogen atom in the benzene molecule substitutes with a –OH group, to give phenol. Therefore, it has the similar aromatic ring structure as in benzene. But its properties are different due to the –OH group. Phenol is mildly acidic (acidic than alcohols). When it loses the hydrogen of the –OH group it forms the phenolate ion, and it undergoes resonance stabilization, which in turn makes phenol a relatively good acid. Also, it is moderately soluble in water, because it can form hydrogen bonds with water. However, phenol evaporates slower than water.
What is the Difference Between Alcohols and Phenols?
Alcohols are organic compounds containing –OH group as the functional group. Phenol is an aromatic hydrocarbon and a derivative of benzene. It is also a type of alcohol. Therefore, the key difference between alcohols and phenols is that the alcohols are organic compounds containing –OH group as an essential component whereas the phenols are a group of alcohols which contains –OH group and a benzene ring as essential components.
As another important difference between alcohols and phenols, generally, the –OH of alcohols attaches to an sp3 hybridized carbon while in phenol, it attaches to an sp2 hybridized carbon. Moreover, phenols are much stronger acids than alcohols.
Below is an infographic on the difference between alcohols and phenols.
Summary – Alcohols vs Phenols
Alcohols are organic compounds. Phenol is a type of alcohol with some characteristic features. The key difference between alcohols and phenols is that the alcohols are organic compounds containing –OH group as an essential component whereas the phenols are a group of alcohols which contains –OH group and a benzene ring as essential components.
1. “Alcohols.” Chemistry LibreTexts, National Science Foundation, 26 Nov. 2018. Available here