Search results
Results from the WOW.Com Content Network
The σ-π model differentiates bonds and lone pairs of σ symmetry from those of π symmetry, while the equivalent-orbital model hybridizes them. The σ-π treatment takes into account molecular symmetry and is better suited to interpretation of aromatic molecules ( Hückel's rule ), although computational calculations of certain molecules tend ...
A molecule with no rings can be represented as a tree with a number of bonds equal to the number of atoms minus one (as in dihydrogen, H 2, with only one sigma bond, or ammonia, NH 3, with 3 sigma bonds). There is no more than 1 sigma bond between any two atoms. Molecules with rings have additional sigma bonds, such as benzene rings, which have ...
Two pi bonds are the maximum that can exist between a given pair of atoms. Quadruple bonds are extremely rare and can be formed only between transition metal atoms, and consist of one sigma bond, two pi bonds and one delta bond. A pi bond is weaker than a sigma bond, but the combination of pi and sigma bond is stronger than either bond by itself.
These bonding modes are sometimes referred to sigma- and pi-bonded. These forms may sometimes interconvert. The sigma bonding mode is more common for higher valence, Lewis-acidic metal centers (e.g., Zn 2+). [1] The pi-bonded mode is observed for low valence, electron-rich metal centers (e.g., Fe(0) and Os(0)). [2]
Sigma and pi bonds in graphene. Sigma bonds result from an overlap of sp 2 hybrid orbitals, whereas pi bonds emerge from tunneling between the protruding p z orbitals. For clarity, only one p z orbital is shown with its three nearest neighbors.
In organic chemistry, neighbouring group participation (NGP, also known as anchimeric assistance) has been defined by the International Union of Pure and Applied Chemistry (IUPAC) as the interaction of a reaction centre with a lone pair of electrons in an atom or the electrons present in a sigma or pi bond contained within the parent molecule but not conjugated with the reaction centre.
Pi bonds occur when two orbitals overlap when they are parallel. [9] For example, a bond between two s-orbital electrons is a sigma bond, because two spheres are always coaxial. In terms of bond order, single bonds have one sigma bond, double bonds consist of one sigma bond and one pi bond, and triple bonds contain one sigma bond and two pi bonds.
Double and triple bonds are usually represented by two or three curved rods, respectively, or alternately by correctly positioned sticks for the sigma and pi bonds. In a good model, the angles between the rods should be the same as the angles between the bonds , and the distances between the centers of the spheres should be proportional to the ...