Orbital is not enlazant – Wikipedia, the free encyclopedia

And Orbital not linked , also know as Non -linking molecular orbital (NBMO, English non-bonding molecular orbital ), It is a molecular orbital whose occupation by electrons does not increase or decrease the order of link between the atoms involved. Non -linking orbitals are often designated with the letter n in molecular orbital diagrams and electron transition notations. Non -linking orbitals are the equivalent in the theory of molecular orbitals of lonely pairs in Lewis structures. The energy level of a non -connecting orbital is typically among the lowest energy of an orbital linked valence layer and the highest energy of a corresponding anti -salad orbital. As such, an orbital without liaison with electrons would be commonly a homo (the busiest molecular orbital).

Generalities [ To edit ]

According to molecular orbital theory, molecular orbitals are often modeled by the linear combination of atomic orbitals. In a simple diatomic molecule such as hydrogen fluoride (

${displaystyle {ce {HF}}}$

), one atom can have many more electrons than the other. A sigma link orbital between atomic orbitals with the same symmetry is created. Some orbitals (for example, orbitals

${displaystyle p_{x}}$

and

${displaystyle p_{y}}$

of fluorine in

${displaystyle {ce {HF}}}$

) They may not have other orbitals with which to combine and become non -linking molecular orbitals. In the example of

${displaystyle {ce {HF}}}$

, the orbitals

${displaystyle p_{x}}$

and

${displaystyle p_{y}}$

They still have the form of the orbitals

${displaystyle p_{x}}$

and

${displaystyle p_{y}}$

, but when they look as molecular orbitals they are not united. The orbital energy does not depend on the length of any link inside the molecule. Its occupation does not increase or decrease the stability of the molecule, in relation to atoms, since its energy is the same in the molecule as in one of the atoms. For example, there are two rigorously non -linking orbitals that are occupied in the fundamental state of the diatomic hydrogen fluoride molecule; These molecular orbitals are located in the fluorine atom and are composed of type atomic orbitals

${displaystyle p}$

whose orientation is perpendicular to the internuclear axis. Therefore, they are unable to overlap and interact with the Valencia orbital of type

${displaystyle s}$

in the hydrogen atom.

Although non -linking orbitals are usually similar to the atomic orbitals of their constituent atom, they are not necessary to be similar. An example of one is not similar is the non -linking orbital of the Alilo anion, whose electronic density is concentrated in the first and third, carbon atoms. ^{[ first ]} ​

In the canonical theory of completely democated molecular orbitals, it is often the case that none of the molecular orbitals of a molecule is strictly of a non -linking nature. However, in the context of localized molecular orbitals, the concept of a full orbital, without link, tends to correspond to the electrons described in terms of Lewis structure as “solitary pairs.”

Representation [ To edit ]

There are several symbols that are used to represent unoccupied non -binding orbitals. Occasionally, it is used n* , in analogy with σ* and π*, but this use is rare. Often, the atomic orbital symbol is used, more often p By orbital

${displaystyle p}$

; others have used the lyrics a For a generic atomic orbital. (According to Bent’s rule, unoccupied orbitals for an element of the main group are almost always of character

${displaystyle p}$

, since the character

${displaystyle s}$

It is stabilized and used to link orbitals. As an exception, the phenyl cation lumo is an atomic orbital

${displaystyle sp^{x}}$

( x ≈ 2), due to the geometric restriction of the benzene ring.) Finally, Woodward and Hoffmann used the lyrics oh For non -linking orbitals (busy or unemployed) in your monograph Conservation of Orbital Symmetry .

Electrons transitions [ To edit ]

Electrons in molecular orbitals without bond may experience electron transitions such as N → σ* O N → π* transitions. For example, transitions N → π* can be seen in ultraviolet-visible spectroscopy of compounds with carbonyl groups, although absorbance is quite weak. ^{[ 2 ]} ​

See also [ To edit ]

References [ To edit ]