The key difference between benzene and phenyl is that benzene is a cyclic hydrocarbon in the shape of a hexagon, containing only carbon and hydrogen atoms, while phenyl is a derivative of benzene, created by the removal of a hydrogen atom. Therefore, benzene contains six hydrogen atoms while phenyl contains five hydrogen atoms.
Benzene is the simplest aromatic hydrocarbon and serves as the parent compound to numerous important aromatic compounds. Phenyl is a hydrocarbon molecule with the formula C6H5. It is actually a derivative of benzene and therefore, has similar properties as benzene.
CONTENTS
1. Overview and Key Difference
2. What is Benzene
3. What is Phenyl
4. Side by Side Comparison – Benzene vs Phenyl in Tabular Form
5. Summary
What is Benzene?
Benzene only has carbon and hydrogen atoms arranged to give a planar structure. It has the molecular formula of C6H6. Benzene structure was found by Kekule in 1872. Because of the aromaticity, it is different from aliphatic compounds.
Its structure and some of the properties are as follows.
Molecular weight: 78 g mole-1
Boiling point: 80.1 oC
Melting point: 5.5 oC
Density: 0.8765 g cm-3
Benzene is a colourless liquid with a sweet odour. It is flammable and evaporates quickly when exposed. Benzene is used as a solvent because it can dissolve a lot of non-polar compounds. However, benzene is slightly soluble in water. The structure of benzene is unique compared to other aliphatic hydrocarbons; therefore, benzene has unique properties.
All the carbons in benzene have three sp2 hybridized orbitals. Two sp2 hybridized orbitals of a carbon overlap with sp2 hybridized orbitals of adjacent carbons in either side. Other sp2 hybridized orbital overlaps with the s orbital of hydrogen to form a σ bond. The electrons in p orbitals of a carbon overlap with the p electrons of carbon atoms in both sides, forming pi bonds. This overlap of electrons happens in all the six carbon atoms and, therefore, produces a system of pi bonds, which are spread over the whole carbon ring. Thus, these electrons are said to be delocalized. The delocalization of the electrons means that there aren’t alternating double and single bonds. Hence, all the C-C bond lengths are the same, and the length is between single and double bond lengths. Since delocalization benzene ring is stable, it is reluctant to undergo addition reactions, unlike other alkenes.
What is Phenyl?
Phenyl is a hydrocarbon molecule with the formula C6H5. This is derived from benzene; therefore, it has similar properties as benzene. However, this differs from benzene due to lack of a hydrogen atom in one carbon. Therefore, the molecular weight of phenyl is 77 g mole-1. Phenyl is abbreviated as Ph. Usually, phenyl is attached to another phenyl group, atom or molecule (this part is known as the substituent).
The carbon atoms of phenyl are sp2 hybridized like in benzene. All the carbons can form three sigma bonds. Two of the sigma bonds are formed with two adjacent carbons so that it will give rise to a ring structure. The other sigma bond is formed with a hydrogen atom. However, in one carbon in the ring, the third sigma bond is formed with another atom or molecule rather than a hydrogen atom. The electrons in p orbitals overlap with each other to form the delocalized electron cloud. Therefore, phenyl has similar C-C bond lengths between all carbons, regardless of having alternating single and double bonds. This C-C bond length is about 1.4 Å. The ring is planar and has a 120o angle between bonds around a carbon.
Due to the substituent group of phenyl, the polarity and other chemical or physical properties change. If the substituent donates electrons to the delocalized electron cloud of the ring, those are known as electron-donating groups (E.g. -OCH3, NH2). If the substituent attracts electrons from the electron cloud, it is known as an electron-withdrawing substituent. (E.g. -NO2, -COOH). Phenyl groups are stable due to their aromaticity, so they don’t easily undergo oxidations or reductions. Further, they are hydrophobic and non-polar.
What is the Difference Between Benzene and Phenyl?
Basically, phenyl is derived from benzene. The key difference between benzene and phenyl is that benzene is a cyclic hydrocarbon in the shape of a hexagon, containing only carbon and hydrogen atoms, while phenyl is a derivative of benzene, created by the removal of a hydrogen atom. Moreover, the molecular formula of benzene is C6H6 and, for phenyl, it is C6H5. Phenyl alone is not as stable as benzene.
Summary – Benzene vs Phenyl
The key difference between benzene and phenyl is that benzene is a cyclic hydrocarbon in the shape of a hexagon, containing only carbon and hydrogen atoms, while phenyl is a derivative of benzene, created by the removal of a hydrogen atom.
Image Courtesy:
1. “Benzene Structural diagram” By Vladsinger – Own work (Public Domain) via Commons Wikimedia
2. “Phenyl radical group” By Samuele Madini – Own work (Public Domain) via Commons Wikimedia