Molecular orbitals trigonal

These compounds are often referred to as hypervalent. The apical bonds in a trigonal bipyramid are described by molecular orbitals constructed from a p-orbital on the central atom and o-bonding orbitals (p- or sp hybrid) on the apical ligands. The molecular orbitals can be drawn as ... 

These conclusions can be drawn by simple inspection of the molecular orbitals of PHS. The next question is the energetics of the interconversions of the various conformations. The result sketched in Fig. 27 refers to the Berry pseudorotation (J5) process of PHS. The square pyramid is a transition state for isomerization of the trigonal bipyramid, but the barrier is extremely small, in agreement with available experimental evidence. The more complex process ... 

The trigonal bond orbitals in the ten valence electron system as well as the two sets of trigonal lone pair orbitals in the 14 valence electron system are superpositions of it orbitals and o orbitals. The formation of such trigonally symmetric molecular orbitals from a-type and w-type molecular orbitals is entirely analogous in character to the formation of the three (sp2) hybrid atomic orbitals from one (s) and two ip) atomic orbitals which was discussed in the preceding section. This can be visualized by looking at the diatomic molecule... 

The application of the angular overlap method to MXg chromophores of trigonal bipyramidal and square p3u-amidal stereochemistry leads to the patterns of Fig. 2 for the energies of the antibonding "d molecular orbitals (dc). The crystal field model leads to a similar pattern. 

Large numbers of five-coordinate copper(II) complexes in several stereochemistries are known. The spectra which have been most studied with a view to interpretation are those of the trigonal bipyramidal complexes, for which assignments have been proposed on the basis of molecular orbital, angular overlap, and crystal-field models. 

The structural and bonding features of this complex comply with the trigonal in-plane conformational preference observed in d10 (olefin)ML2 complexes. In molecular orbital terms, the dominant bonding interaction is between the b2 HOMO of the ML2 fragment and the ethylene n LUMO283. 

Formulate the bonding in NH2 in terms of delocalized molecular orbitals. The molecule is trigonal-pyramidal (C3V point group). Compare the general molecular-orbital description with a localized tetrahedral model for NH3. Discuss the values of the following bond angles H—N—H, 107° H— P—H (in PH2), 94° and F—N —F (in NF3 ), 103 °. 

Boron trifluoride has a trigonal-planar structure. Formulate the bonding in terms of molecular orbitals for the Dsjj symmetry. In addition, construct wave functions for three equivalent sp2 hybrid orbitals, using the 2px, 2p, and 2s boron valence orbitals, which may be used to form three localized bonds with the three fluorines. Compare and contrast the molecular-orbital and the hybrid-orbital descriptions. 

A possible justification for frontside attack in electrophilic substitution is that ab initio molecular orbital calculations for the CH5+ cation, the species that would be formed if H+ attacked methane, indicate that the most stable structure would not be a trigonal bipyramid, in which carbon uses a p orbital to bond to two protons, but would be a relatively unsymmetrical structure that has a smallest H—C—H bond angle of about 37° (Figure 4.10).85 For further discussion of SB2 substitution on carbon, see Section 10.3.86... 

Lehn and Wipff (72) and Gorenstein and co-workers (73-80) have proposed on the basis of molecular orbital calculations that stereoelectronic effects similar to those observed in esters and amides play also an important role in the hydrolysis of phosphate esters. For instance, calculations suggest that the axial P — OR bond in the trigonal bipyramid conformation 120 is weaker than that in the conformation 121 because in the former, the oxygen atom of the equatorial OR group has an electron pair anti peri planar to the axial P — OR bond. Experimental results tend to support this interesting proposal but additional experiments are needed before unambiguous conclusions can be reached (81). 

In contrast to closed shell molecules, free radicals are species which have an odd number of electrons. Simply speaking, all electrons in free radical species are considered to be paired up, except for one orbital which contains the single electron. The molecular orbital which describes the distribution of this odd electron is called the SOMO (singly occupied MO). In the ground state of the radical, the SOMO is also the HOMO. In a carbon-based free radical the SOMO is generally strongly localized to a trigonal carbon atom. 

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