Overlap of orbitals

The concepts of directed valence and orbital hybridization were developed by Linus Pauling soon after the description of the hydrogen molecule by the valence bond theory. These concepts were applied to an issue of specific concern to organic chemistry, the tetrahedral orientation of the bonds to tetracoordinate carbon. Pauling reasoned that because covalent bonds require mutual overlap of orbitals, stronger bonds would result from better overlap. Orbitals that possess directional properties, such as p orbitals, should therefore be more effective than spherically symmetric 5 orbitals. 

FIGURE 15.9 Overlap of orbitals in an antarafacial thermal 2+4 cycloaddition. 

This follows from the principle that bonds are formed only by overlap of orbitals of the same sign. Since this is a concerted reaction, the hydrogen orbital in the transition state... 

In the bond framework in Figure 10-18. all the bonds form from end-on overlap of orbitals directed toward each other. As illustrated by the three examples in Figure 10-20. this type of overlap gives high electron density distributed symmetrically along the intemuclear axis. A bond of this type is called a sigma (cr) bond, and a bonding orbital that describes a cr bond is a (7 orbital. 

Overlap integral a measure of the extent of overlap of orbitals on neighboring atoms. 

The requirement for coplanarity of the H-C-C-L unit arises from a need for proper overlap of orbitals in the developing n bond of the alkene that is being formed. 

The overlap of orbitals on Fe with the molecular orbitals on the cyclopentadienyl ion. 

This is synonymous with the region of significant overlap of orbital charge distributions, where the Pauli restriction (1.6) and quantal superposition effects become important. 

In ethylene, there are two types of bonds. Sigma (tr) bonds have the overlap of the orbitals on a line between the two atoms involved in the covalent bond. In ethylene, the C-H bonds and one of the C-C bonds are sigma bonds. Pi (ir) bonds have the overlap of orbitals above and below a line through the two nuclei of the atoms involved in the bond. A double bond is always composed of one sigma and one pi bond. A carbon-to-carbon triple bond results from the... 

However, there are other possibilities. What if instead of an unsuccessful overlap of orbitals the overlap occurs in a suitable way, and instead of repulsion, attraction between the ion and the electrode atoms results In this case strong bonds may be formed between the ion and the electrode. These bonds are the result of donation or acceptance of electrons by the ion, and are responsible for the chemisorption of molecules. 

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