Sulfur dihedral angles

The molecular and crystal stmctures of 2-phenylbenzotellurazole were determined by X-ray (89KGS1690). The dihedral angle between the planes of the five-membered heterocycle and 2-phenyl ring is 31.2°. In contrast to benzoisotel-lurazole, no shortened intermolecular Te- N contacts were found in the crystal stmcture of 2-phenylbenzotellurazole. Consequently, no anomalies in solubility and melting point were revealed for this compound as compared with its sulfur and selenium congeners. 

There are two possible Cs conformations of the Sy homocycle exo and endo. The exo global minimum (Fig. 2) lies 15 kJ mol below the endo-form. Both conformers undergo facile pseudorotation through C2 transition states, with barriers of less than 4 kJ mol [54]. The exo-conformer possesses the geometry found in the sulfur allotropes y-Sy and 5-Sy [72]. This Cs structure has four bonds near the length of a normal S-S bond and one rather long bond of 215 pm with a dihedral angle of 0°. 

As mentioned in the Introduction, in iron—sulfur proteins, the hyperfine shifts of the nuclei of the coordinating cysteines are essentially contact in origin (21, 22). In the case of [Fe4S4l (17) and [FegS4] (112) cluster, it has been shown that the hyperfine shift of the cysteinyl H/3 and Ca nuclei can be related to the value of the Fe-Sy-C/S-H/S/Ca dihedral angle (6) through a Karplus-type relationship of the form... 

The structure of S2F2 resembles that of H202 with a dihedral angle of about 88 °, and SF4 is an irregular tetrahedron. As expected, the SFs molecule is a regular octahedron. The structures of all these sulfur fluorides are shown in Figure 15.1. 

The chain derives from the 84 one by addition of one more sulfur atom, so that the dihedral angle of 90° is maintained. In doing so, we obtain structures c and d (Fig. 1), the cis and (d and /) trans forms of the 85 chain. 8imilarly, by further addition of one sulfur atom, it can be shown that for an 8g chain three (enantiomorphic) isomers will result (cis,cis trans,trans and cis,trans, each d and /, respectively). The cis-Si and cis,cis-S ions may be regarded as parts of the 8g ring... 

The disulfide group has two no bands in the near UV that are weak in absorption but can give rise to substantial CD bands. The two n orbitals arise from lone pairs on the sulfurs, and the o orbital is the antibonding orbital formed from the same o orbitals responsible for the S—S bond. When the disulfide dihedral angle xss 90°, the preferred dihedral angle for an... 

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