Conformation, molecular eclipsed

Ethane is the simplest hydrocarbon that can have distinct conformations Two the stag gered conformation and the eclipsed conformation, deserve special mention and are illustrated with molecular models m Figure 3 1... 

Torsional strain refers to the component of total molecular energy that results from nonoptimal arrangement of vicinal bonds, as in the eclipsed conformation of ethane. The origin and stereoelectronic nature of torsional strain were discussed in Section 1.1.1. The... 

Molecular structure of [M(t) -CsHs)2-(CO)2j. For M = Ti the CsHs rings are eclipsed as shown here, but for M = Hf they are staggered . Essentially the same structure is found in other [M( ) -CsHs)2L2] molecules, but the conformation of the two CsHs rings varies in an apparently unsystematic manner. 

Eclipsed conformation, 94 molecular model of, 94 Edman, Pehr Victor, 1031 Ed man degradation, 1031-1032 mechanism of. 1032 Eicosanoid, 1067-1070... 

The molecular orbital interactions are almost independent of the conformation of the sandwich complex with respect to rotation of the Cp rings. Both the staggered (Dsd) as well as the eclipsed conformation (Dsh) possess similar binding energies... 

As a consequence of the molecular orbital interactions, ferrocene adopts an axially symmetrical sandwich structure with two parallel Cp ligands with a distance of 3.32 A (eclipsed conformation) and ten identical Fe-C distances of 2.06 A as well as ten identical C-C distances of 1.43 A [12]. Deviation of the parallel Cp arrangement results in a loss of binding energy owing to a less efficient orbital overlap [8]. All ten C-H bonds are slightly tilted toward the Fe center, as judged from neutron-diffraction studies [13]. 

In the Group XIV compounds the two rings are not parallel, due to the influence of the metal lone pair, giving rise to a bent-sandwich molecular structure142 (C2V symmetry), different from that in other stable cyclopentadienyl derivatives, such as Fe(Cp)2, where the two rings are parallel (D5h symmetry in the eclipsed conformation and D5d symmetry in the staggered one). 

In this connection, in order to judge the level of these molecular rearrangements, the solid state X-ray structures of ferrocene and ferrocenium ion could be compared. Unfortunately, the molecular disorder caused by the rotation of the cyclopentadienyl rings in ferrocene means that the comparison procedure is far from simple and, in fact, the first results were interpreted in terms of a staggered conformation of the two cyclopentadienyl rings. It is now believed that the eclipsed conformation is the more stable (with a rotation angle of about 10°).2 However, as the rotational barrier is notably low (about 4 kJ mol-1), the conformation that one observes is probably that imposed by crystal packing forces. 

In support of the electrochemical evidence, the molecular structure of the biferrocenium ion in [( -CsF Fe -CsfLOf -CsfLOFe -CsHs)] [I3] shows that both pairs of cyclopentadienyl rings have an eclipsed conformation, Figure 16. Furthermore, the mean Fe-Cp(Centroid) distance is equivalent in both the ferrocenyl units and equal to 1.68 A. Speculatively, this value is intermediate between the values previously observed for ferrocene and ferrocenium ions, thus supporting charge delocalization between the two centres.27... 

Determine the qualitative form of the molecular orbitals for the eclipsed conformation of ferrocene. 

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