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A diatomic molecular orbital diagram is used to understand the bonding of a diatomic molecule. MO diagrams can be used to deduce magnetic properties of a molecule and how they change with ionization. They also give insight to the bond order of the molecule, how many bonds are shared between the two atoms. [12]
Thermolysis converts 1 to (E,E) geometric isomer 2, but 3 to (E,Z) isomer 4.. The Woodward–Hoffmann rules (or the pericyclic selection rules) [1] are a set of rules devised by Robert Burns Woodward and Roald Hoffmann to rationalize or predict certain aspects of the stereochemistry and activation energy of pericyclic reactions, an important class of reactions in organic chemistry.
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 addition to providing a unified explanation of diverse aspects of chemical reactivity and selectivity, it agrees with the predictions of the Woodward–Hoffmann orbital symmetry and Dewar–Zimmerman aromatic transition state treatments of thermal pericyclic reactions, which are summarized in the following selection rule:
To summarize, we are assuming that: (1) the energy of an electron in an isolated C(2p z) orbital is =; (2) the energy of interaction between C(2p z) orbitals on adjacent carbons i and j (i.e., i and j are connected by a σ-bond) is =; (3) orbitals on carbons not joined in this way are assumed not to interact, so = for nonadjacent i and j; and ...
The molecular orbital diagram for the final state describes the electronic nature of the molecule in an excited state. Although in MO theory some molecular orbitals may hold electrons that are more localized between specific pairs of molecular atoms, other orbitals may hold electrons that are spread more uniformly over the molecule.
Figure 3. Möbius (left) and Hückel (right) orbital arrays. The two orbital arrays in Figure 3 are just examples and do not correspond to real systems. In inspecting the Möbius one on the left, plus–minus overlaps are seen between orbital pairs 2-3, 3-4, 4-5, 5-6, and 6-1, corresponding to an odd number (5), as required by a Möbius system.
where is a molecular orbital represented as the sum of n atomic orbitals , each multiplied by a corresponding coefficient , and r (numbered 1 to n) represents which atomic orbital is combined in the term. The coefficients are the weights of the contributions of the n atomic orbitals to the molecular orbital.