A pi bond and an anti-bonding orbital are two different concepts in chemistry. Here's an explanation of each:
Pi Bond: A pi (π) bond is a type of covalent bond that forms between two adjacent atoms when there is a sideways overlap of atomic orbitals. Pi bonds are commonly observed in molecules with double or triple bonds. The pi bond is formed by the overlap of p-orbitals or d-orbitals that are parallel to each other. It is characterized by the electron density above and below the internuclear axis, forming a cylindrical electron cloud.
Anti-bonding Orbital: An anti-bonding orbital, also known as an antibonding orbital, is an orbital that has higher energy than the corresponding bonding orbital. It is formed by the destructive interference of two atomic orbitals that are out of phase with each other. Anti-bonding orbitals have a nodal plane between the nuclei of the bonded atoms, which means there is zero electron density along the internuclear axis. These orbitals weaken the bonding interaction and can destabilize a molecule.
In summary, the key difference between a pi bond and an anti-bonding orbital is that a pi bond is a specific type of covalent bond formed by the sideways overlap of atomic orbitals, while an anti-bonding orbital refers to an orbital that has higher energy than the corresponding bonding orbital and weakens the bonding interaction in a molecule.