Eclipsed arrangement

To probe further the bonding descriptions of the transition metal metallocenes it is instructive to assemble a back of the envelope MO scheme. The available structural evidence (249, 280) indicates that the energies of the staggered (DSd) and eclipsed conformations are rather close. Thus, in the solid state, ferrocene adopts the DSd conformation (106), while the eclipsed arrange-... 

In butane, CH3CH2CH2CH3, a 360° rotation about the central C-C bond allows the molecule to pass through three different eclipsed arrangements (8, 10, 12), and three different staggered arrangements (7, 9, 11), as shown in Figure 5-7. Experiment shows that butane favors the staggered form... 

Analysis of the low temperature VT NMR (,9F and H) and 19F- H heteronuclear NOE spectra of 65 and 66 in conjunction with molecular modeling has revealed the presence of an equilibrium between two conformers in protic solvent systems. Interpretation of the temperature dependence of the coupling constants between H2 and H3 for 65 shows that one of these conformers (conformer C) has an unusual near-eclipsed arrangement around the H2 -C2 -C3,-H3 dihedral angle (7H2- H3-= 5.2 Hz, corresponding to the H2 -C2 -C3 -H3 torsion angle of 124° based on the MM2 calculation), and is found to be more prevalent at ambient temperatures. The... 

The cyclic diyne (55) has C—C=C angles of 159.3° as determined by an X-ray analysis, which is close to the value found in cyclooctyne by electron diffraction 161 (see above). The carbon framework of the molecule is almost planar with the two CH2—CH2 units in an almost eclipsed arrangement. This and the transannular repulsion between the ii-moieties leads to the large value of 1.57 A for the C3—C4 single bond. All other structural parameters seem to be normal.164)... 

Other features are Tc-Obridge bond distances of 1.90-1.92 A and the near-eclipsed arrangement of the donor atoms of the two Tc centers as shown in 48, in which the near-eclipsed atoms are Cl and S (517). The occurrence of linear d2-d2 [Mv203]4+ (M = Tc, Re) cores is explained... 

The [Re2Clg] anion is the progenitor of Re-Re quadruple bonds both historically and synthetically. The recognition of a bond of order four in Cs2 [Re2Clg], as reflected in the eclipsed arrangement of the two ReCU fragments, and the short Re-Re distance, initiated studies of these metal-metal linkages... 

H20, which has very similar cell dimensions and is very likely to be isomorphous to Wu s A salt, may be necessary. As shown in Figure 3, the structure of the [P2W18O62] anion exhibits the P-Dawson structure, which can be regarded as a fused product of a-A-PWg and P-A-PWg groups in the eclipsed arrangement of the two belt W6 groups. This structure is consistent with the "P and W NMR spectra recorded in solutions. "... 

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