Intermediate geometries

One way to describe the electronic situation at an intermediate geometry can be obtained by starting off with MH and mixing in a contribution from this higher energy electronic state as a configuration interaction, viz. 

Radical cations derived from 1,5-hexadiene systems illustrate major differences between the potential surfaces of radical cations and neutral precursors. On the precursor potential surface, the states of intermediate geometry are saddle points (transition structures), but pronounced minima (Fig. 6.14) on the radical cation potential surface. 

Among the phosphorylated analogues, the aldonic acids are better enzyme inhibitors than the corresponding alcohols, and the alcohols are better inhibitors than the corresponding aldehydes. This may reflect the acid and alcohol molecules ability to mimic the postulated enediol intermediate geometry. 

Aromatic n n interactions (sometimes called n n stacking interactions) occur between aromatic rings, often in situations where one is relatively electron rich and one is electron poor. There are two general types of -interactions face-to-face and edge-to-face, although a wide variety of intermediate geometries are... 

Figure 24 displays the high energy (E > 25,000 cm-1) region of the room temperature electronic absorption spectrum for Zn(bpy)(tdt), where bpy = 2,2 -bipyridine. The LLCT transition occurs at 22,470 cm-1 (445 nm) with very weak absorption intensity (e = 72 M 1cm 1). The origin of the weak LLCT is a function of the symmetry of this psuedo-tetrahedral complex. A MO diagram for Zn(bpy)(tdt), derived from extended Hiickel calculations, is presented in Fig. 25. Irrespective of whether the metallo(diimine)(dithiolene) complex is square-planar or psuedo-tetrahedral, the point symmetry is C2V, and all intermediate geometries possess C2 symmetry. When the dithiolene and diimine planes are orthogonal (psuedo-tetrahedral geometry) the HOMO — LUMO transition represents a b2 —> b one-electron promotion and is electric dipole forbidden. However, the HOMO —> LUMO transition in a square-planar...

There may not be a TS connecting two minima directly. The algorithm may then find an intermediate geometry having a gradient substantially different from zero, i.e. no nearby stationary point. 

The examination of coordinate transformations as local contractions and expansions of decorations about the poles of the principal rotational axes on the unit sphere for objects of Oh symmetry leads to intermediate geometries corresponding to particular Archimedean polyhedra related to the cube. In a similar manner, partial contractions and expansions of the decorations of the regular orbit of Ih point symmetry, i.e. the vertices of the great rhombicosidodecahedron, leads to the remaining polyhedra within the icosahedral family of Archimedean structures and orbits of Ih. 

Fig. 7 Orbital correlation diagram for singlet Cr(CO)j between trigonal bipyramid (TBP), Dji, and square planar (SP), C v, geometries. AH intermediate geometries have C2v symmetry. Dst, and C v, are both supergroups of C2v...

The potassium analouge [KTi(O-/-Pr)5]0o is structurally similar to Fig. 36, however, the infinite alternating chain is nonlinear. The potassium atoms are five coordinated and appear to adopt an intermediate geometry between square base prismatic and trigonal bipyramidal. The potassium atoms interact with four of the five isopropoxides of titanium using /x-O-i-Pr and ji3-0-/-Pr ligands. 

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