Difference Between Benzyl and Phenyl

Benzyl and phenyl are two common organic compounds that are often confused with each other. Both compounds contain a benzene ring, but there are important differences between them in terms of their chemical structure and properties. In this essay, we will explore the difference between benzyl and phenyl in detail.

What is Benzyl?

Benzyl is a functional group, consisting of a benzene ring, attached to a CH₂ group. Its chemical formula is C₆H₅CH₂–. Benzyl is a monovalent radical derived from toluene.

• The abbreviation "Bn" is used to represent the benzyl group. For example, the benzyl alcohol can be marked as BnOH.

• The position of the first C atom bonded to an aromatic ring is described as benzylic. The benzylic positions are characterized by enhanced reactivity. It is due to the low dissociation energy of the benzyl C−H bonds. The energy, necessary for bond dissociation of the benzyl C-H bond is 90 kcal/mol, while for the methyl C−H bond it is 105 kcal/mol, and for the ethyl C−H bond it is 101 kcal/mol.

• The aromatic ring has a stabilizing role for the benzyl radicals. However, the weak C−H bond impacts the stability of the benzyl radical. Because of the weaker C-H bond, benzylic substituents show enhanced reactivity in free radical halogenation, oxidation, hydrogenolysis, etc.

• Chemical compounds, containing a benzyl group are benzyl methyl, benzyl bromide, benzyl chloroformate, benzyl amine, etc.

• Benzyl is used in organic synthesis as a protecting group for carboxylic acids and alcohols.

What is Phenyl?

Phenyl is a cyclic functional group with the formula C₆H₅-. It is a monovalent aryl radical, closely related to benzene and derived from it by removal of one H atom. The phenyl group has six C atoms bonded in a hexagonal ring. One of these atoms is bonded to a substituent, and the other five are bonded to hydrogen atoms.

• The abbreviation "Ph" is used to represent the phenyl group. For example, the benzene can be denoted as PhH.

• The dissociation energy of the phenyl C−H bonds is higher than this of other C-H bonds. The energy necessary for bond dissociation of the phenyl C-H bond is 113 kcal/mol, while for the methyl C−H bond it is 105 kcal/mol, and for the ethyl C−H bond it is 101 kcal/mol.

• The properties of the aromatic molecular orbitals additionally increase the stability of the phenyl group. Phenyl substances are hydrophobic and tend to resist reduction and oxidation.

• Chemical compounds, containing phenyl group are triphenylmethane, chlorobenzene, phenol, etc.

• Compounds containing phenyl groups are used in the medicine. For example, Atorvastatin is used to lower cholesterol, Fexofenadine is used to treat allergies.

Differences Benzyl and Phenyl

One of the most important differences between benzyl and phenyl is the nature of the bond between the benzene ring and the attached group. In benzyl, the CH2 group is attached to the benzene ring through a single bond, which means that the two groups are directly connected. In phenyl, there are no other groups attached to the benzene ring, which means that it is an unsubstituted benzene ring.

Another important difference between benzyl and phenyl is their reactivity. Benzyl is more reactive than phenyl because the CH₂ group is a weakly acidic functional group that can be easily deprotonated. This means that benzyl can react with strong bases to form a carbanion, which is a highly reactive intermediate. In contrast, phenyl is much less reactive because there are no other functional groups attached to the benzene ring that can be easily deprotonated.

Benzyl and phenyl also differ in their physical properties. Benzyl is a colorless liquid with a sweet aroma and a boiling point of 179°C. It is soluble in most organic solvents, but insoluble in water. Phenyl, on the other hand, is a colorless crystalline solid with a melting point of 80°C. It is insoluble in water and only slightly soluble in most organic solvents.

In terms of their uses, benzyl and phenyl have different applications. Benzyl is commonly used as a solvent in the production of various chemicals such as perfumes, dyes, and pharmaceuticals. It is also used as a starting material for the synthesis of other chemicals such as benzyl chloride and phenylacetic acid. Phenyl, on the other hand, is often used as a substituent in organic chemistry to modify the properties of other compounds. For example, the introduction of a phenyl group to a compound can increase its hydrophobicity and alter its biological activity.

The following table highlights the major differences between Benzyl and Phenyl:

Conclusion

In summary, benzyl and phenyl are two organic compounds that contain a benzene ring. However, they differ in their chemical structure, reactivity, physical properties, and uses. Benzyl contains a benzene ring and a CH2 group attached to it through a single bond, while phenyl contains an unsubstituted benzene ring.

Benzyl is more reactive than phenyl because of the presence of the CH2 group, and it is commonly used as a solvent and starting material for the synthesis of other chemicals. Phenyl is often used as a substituent in organic chemistry to modify the properties of other compounds.

Vineet Nanda

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Updated on: 21-Aug-2023

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