Ethylene bonding molecular orbitals

This displays the HOMO of ethylene. This is an occupied bonding molecular orbital. 

What is wrong with the following sentence "The it bonding molecular orbital in ethylene results from sideways overlap of two p atomic orbitals."... 

Let us now apply these results to the ethylene molecule (Fig. 14), for which we attempt to build the bonding molecular orbitals. Clearly there are three symmetry planes. Two of these are of special interest... 

FlO. 2. The ethylene-platinum bonding (a), the common representation emphasizing w electron donation (6), the e-bonding molecular orbital (c), the 7r-bonding molecular orbital. 

Note how we have resorted to another form of representation of the ethane, ethylene, and acetylene molecules here, representations that are probably familiar to you (see Section 1.1). These line drawings are simpler, much easier to draw, and clearly show how the atoms are bonded - we use a line to indicate the bonding molecular orbital. They do not show the difference between a and rr bonds, however. We also introduce here the way in which we can represent the tetrahedral array of bonds around carbon in a two-dimensional drawing. This is to use wedges and dots for bonds instead of lines. By convention, the wedge means the bond is coming towards you, out of the plane of the paper. The dotted bond means it is going away from you, behind the plane of the paper. We shall discuss stereochemical representations in more detail later (see Section 3.1). 

Use orbital interaction analysis to derive the bonding molecular orbitals of ethyl -benzenium ion. Consider ethylbenzenium ion to be the result of the interaction of a phenyl group, C6H5, and ethylene, C2H4, with the appropriate number of electrons. (Direct evidence for the existence of ethylbenzenium ion was obtained by Fornarini,... 

Structure of the double bond in ethylene. The first pair of electrons forms a a bond. The second pair forms a it bond. The it bond has its electron density centered in two lobes, above and below the bonding molecular orbital constitute one bond. 

Two more electrons must go into the carbon-carbon bonding region to form the double bond in ethylene. Each carbon atom still has an unhybridized p orbital, and these overlap to form a pi-bonding molecular orbital. The two electrons in this orbital form... 

In the pi bonding molecular orbital of ethylene, the lobes that overlap in the bonding region between the nuclei are in phase that is, they have the same sign (+ overlaps with +, and — overlaps with —). We call this reinforcement constructive overlap. Constructive overlap is an important feature of all bonding molecular orbitals. 

The 7t bonding molecular orbital in ethylene results from the combination of twop atomic orbitals with the same algebraic sign. (A second molecular orbital can form by the combination of two p orbitals with opposite algebraic signs, but it is an antibonding orbital.)... 

The kind of bond with respect to type B may be interpreted analogous to the ethylene complexes as a dative x-alternating effect (Fig. 24). As opposed to type A complexes, the properties of type B complexes are determined in a characteristic way by the back donation into the unoccupied n molecular orbital (LUMO) of the double bond (Fig. 24). This strengthens the metal-ligand bond, as proved by a shorter interatomic distance, and weakens the double bond (occupying anti bonding molecular orbitals), as is evident by a widened PC distance. The phosphaalkene P atom has, so to speak, more of a phosphane... 

The valence electronic structure of the ethylene molecule, C2H4, can be described in terms of a set of a bonding molecular orbitals approximately localized in the CC and CH bonds... 

In the structure of Zeise s salt, the ethylene occupies the fourth coordination site of the square planar complex with the CC axis perpendicular to the platinum-ligand plane. In this compound, the dsp2 hybridised s orbital of Pt overlaps with / -bonding molecular orbitals of ethylene. Simultaneously, the filled dp orbital of Pt overlaps with p orbital of C2H4. 

Unlike the pi bonding molecular orbitals in ethylene, those in benzene form delocalized molecular orbitals, which are not confined between two adjacent bonding atoms, but actually extend over three or more atoms. Therefore, electrons residing in any of these orbitals are free to move around the benzene ring. For this reason, the structure of benzene is sometimes represented as... 

From the electronic structure point of view, there are similarities between the two SS and SA bonding molecular orbitals of the xr complex (3-42 and 3-43, left-hand side) and the corresponding orbitals of the metallacyclopropane. The latter can be represented schematically by considering the in-phase and out-of-phase combinations of two localized orbitals, each of which characterizes a CTmc bond (3-42 and 3-43, right-hand side). ° The first combination corresponds to the orbital tx +z of the molecular ethylene complex, the second to the orbital yz + tt. ... 

Two more electrons must go into the carbon-carbon bonding region to form the double bond in ethylene. Each carbon atom still has an unhybridized p orbital, and these overlap to form a pi-bonding molecular orbital. The two electrons in this orbital form the second bond between the double-bonded carbon atoms. For pi overlap to occur, these p orbitals must be ptarallel, which requires that the two carbon atoms be oriented with all their C—H bonds in a single plane (Figure 7-1). Half of the pi-bonding... 

The expectation value of the bond-order operator is a measure of the strength of that bond, as illustrated by the simple example of ethylene. Modelling this by two TT-orbitals with two electrons shared between them it is easily shown that the bonding molecular orbital has a bond-order value of +1, while the antibonding molecular orbital has a bond-order value of —1. Thus, a larger bond-order value implies a stronger bond. 

Atomic Structure The Nucleus Atomic Structure Orbitals 4 Atomic Structure Electron Configurations 6 Development of Chemical Bonding Theory 7 The Nature of Chemical Bonds Valence Bond Theory sp Hybrid Orbitals and the Structure of Methane 12 sp Hybrid Orbitals and the Structure of Ethane 13 sp2 Hybrid Orbitals and the Structure of Ethylene 14 sp Hybrid Orbitals and the Structure of Acetylene 17 Hybridization of Nitrogen, Oxygen, Phosphorus, and Sulfur 18 The Nature of Chemical Bonds Molecular Orbital Theory 20 Drawing Chemical Structures 21 Summary 24... 

Consideration of the electronic stracture and geometry of the first excited (triplet-spin) state of ethylene provides an illustration of non-bonded repulsions between singly-occupied overlapping orbitals. Ethylene has two x-electrons that occupy a bonding molecular orbital in the lowest-energy configuration. If one of these electrons is excited into the antibonding 71 orbital, then ) con-... 

Two types of electronic transitions are of special interest to photochemists. The first is observed in unsaturated compounds such as ethylene, benzene, and pyridine and is called a ir-jr transition. It is caused by an electron jump from a 7r-bonding molecular orbital to a ir -antibonding molecular orbital. Singlet-singlet ir-jr transitions are usually very probable and are progressively shifted to longer wavelei hs as the number of conjugated atoms in molecules increases. 

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