Alcohols vs Phenols
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.
The characteristic of the alcohol family is the presence of a –OH functional group (hydroxyl group). Normally, this –OH group is attached to a sp3 hybridized carbon. The simplest member of the family is methyl alcohol, which is also known as methanol. Alcohols can be classified into three groups as primary, secondary and tertiary. This classification is based on the degree of substitution of carbon to which the hydroxyl group is directly attached. If the carbon has only one other carbon attached to it, the carbon is said to be a primary carbon and the alcohol is a primary alcohol. If the carbon with the hydroxyl group is attached to two other carbons, then that is a secondary alcohol and so on. Alcohols are named with a suffix –ol according to the IUPAC nomenclature. First, the longest continuous carbon chain to which the hydroxyl group is directly attached should be selected. Then the name of the corresponding alkane is changed by dropping the final e and adding the suffix ol.
Alcohols have a higher boiling point than the corresponding hydrocarbons or ethers. The reason is the presence of intermolecular interaction between alcohol molecules through hydrogen bonding. If the R group is small, alcohols are miscible with water. But as the R group is becoming larger, it tends to be hydrophobic. Alcohols are polar. The C-O bond and O-H bonds contribute to the polarity of the molecule. Polarization of the O-H bond makes the hydrogen partially positive and explains the acidity of alcohols. Alcohols are weak acids, and the acidity is close to that of water. –OH is a poor leaving group, because 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 is directly attached to 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.
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 odor. Its structure and some of the properties are given below.
Molecular weight: 94 g mole-1
Boiling point: 181 oC
Melting point: 40.5 oC
Density: 1.07 g cm-3
Hydrogen atom in the benzene molecule is substituted 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 is resonance stabilized, which in turn makes phenol a relatively good acid. And it is moderately soluble in water, because it can form hydrogen bonds with water. Phenol evaporates slower than water.
What is the difference between alcohol and phenol?
• Phenol is also belonging into the alcohol family. They are alcohols with aromatic rings.
• Generally in alcohols, the –OH is attached to a sp3 hybridized carbon. But in phenol it is attached to a sp2 hybridized carbon.
• Phenols are much stronger acids than alcohols.
• Phenols can be distinguished from alcohols, because phenols dissolve in aqueous NaOH, whereas alcohols with six carbon atoms do not.