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In chemistry, orbital hybridisation (or hybridization) is the concept of mixing atomic orbitals to form new hybrid orbitals (with different energies, shapes, etc., than the component atomic orbitals) suitable for the pairing of electrons to form chemical bonds in valence bond theory.
In organic chemistry, planar, three-connected carbon centers that are trigonal planar are often described as having sp 2 hybridization. [2] [3] Nitrogen inversion is the distortion of pyramidal amines through a transition state that is trigonal planar. Pyramidalization is a distortion of this molecular shape towards a tetrahedral molecular ...
Planarity results from the sp 2-hybridization of the mutually double-bonded carbon and the nitrogen atoms. The C=N distance is 1.29–1.31 Å for nonconjugated imines and 1.35 Å for conjugated imines. By contrast, C−N distances in amines and nitriles are 1.47 and 1.16 Å respectively. [4]
In traditional hybridisation theory, the hybrid orbitals are all equivalent. [12] [27] Namely the atomic s and p orbital(s) are combined to give four sp i 3 = 1 ⁄ √ 4 (s + √ 3 p i) orbitals, three sp i 2 = 1 ⁄ √ 3 (s + √ 2 p i) orbitals, or two sp i = 1 ⁄ √ 2 (s + p i) orbitals. These combinations are chosen to satisfy two ...
Bredt's rule also applies to carbocations and, to a lesser degree, free radicals, because these intermediates also prefer a planar geometry with 120° angles and sp 2 hybridization. It generally does not apply to hypervalent heteroatoms, although they are commonly written with a formal double bond. [6]
The nitrogen atom of an ideal amide is sp 2-hybridized due to resonance, and sp 2-hybridized atoms have trigonal planar bond geometry. As a pyramidal bond geometry is forced upon the nitrogen atom by the ring strain, the resonance of the amide bond is reduced, and the carbonyl becomes more ketone-like.
With nitrogen, we see the two molecular orbitals mixing and the energy repulsion. This is the reasoning for the rearrangement from a more familiar diagram. The σ from the 2p is more non-bonding due to mixing, and same with the 2s σ. This also causes a large jump in energy in the 2p σ* orbital.
In organic chemistry, molecules which have a trigonal pyramidal geometry are sometimes described as sp 3 hybridized. The AXE method for VSEPR theory states that the classification is AX 3 E 1. Phosphine, an example of a molecule with a trigonal pyramidal geometry.