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Most orbital overlaps that do not include the s-orbital, or have different internuclear axes (for example p x + p y overlap, which does not apply to an s-orbital) are generally all pi bonds. Pi bonds are more diffuse bonds than the sigma bonds. Electrons in pi bonds are sometimes referred to as pi electrons. Molecular fragments joined by a pi ...
Antibonding orbitals are often labelled with an asterisk (*) on molecular orbital diagrams. In homonuclear diatomic molecules, σ* (sigma star) antibonding orbitals have no nodal planes passing through the two nuclei, like sigma bonds, and π* (pi star) orbitals have one nodal plane passing through the two nuclei, like pi bonds.
For example, the absorption spectrum for ethane shows a σ → σ* transition at 135 nm and that of water a n → σ* transition at 167 nm with an extinction coefficient of 7,000. Benzene has three aromatic π → π* transitions; two E-bands at 180 and 200 nm and one B-band at 255 nm with extinction coefficients respectively 60,000, 8,000 and 215.
Complete acetylene (H–C≡C–H) molecular orbital set. The left column shows MO's which are occupied in the ground state, with the lowest-energy orbital at the top. The white and grey line visible in some MO's is the molecular axis passing through the nuclei. The orbital wave functions are positive in the red regions and negative in the blue.
In chemistry, π backbonding is a π-bonding interaction between a filled (or half filled) orbital of a transition metal atom and a vacant orbital on an adjacent ion or molecule. [ 1 ] [ 2 ] In this type of interaction, electrons from the metal are used to bond to the ligand , which dissipates excess negative charge and stabilizes the metal.
In chemistry, π-effects or π-interactions are a type of non-covalent interaction that involves π systems.Just like in an electrostatic interaction where a region of negative charge interacts with a positive charge, the electron-rich π system can interact with a metal (cationic or neutral), an anion, another molecule and even another π system. [1]
These orbitals and typically given the notation σ (sigma bonding), π (pi bonding), n (occupied nonbonding orbital, "lone pair"), p (unoccupied nonbonding orbital, "empty p orbital"; the symbol n* for unoccupied nonbonding orbital is seldom used), π* (pi antibonding), and σ* (sigma antibonding). (Woodward and Hoffmann use ω for nonbonding ...
For the hydrogen fluoride molecule, for example, two F lone pairs are essentially unhybridized p orbitals of π symmetry, while the other is an sp x hydrid orbital of σ symmetry. An analogous consideration applies to water (one O lone pair is in a pure p orbital, another is in an sp x hybrid orbital).