Ring torsion

Fig. 9.33 Scatterplot of the first two principal components for the ring torsion angles...

Fig. 18. Top transition coordinates (with symmetry species) of conformational transition states of cyclohexane (top and side views). Hydrogen displacements are omitted. The displacement amplitudes given are towards the C2v-symmetric boat form, and towards >2-symmetric twist forms (from left), respectively. Inversion of these displacements leads to the chair and an equivalent T>2-form, respectively. Displacements of obscured atoms are given as open arrows, obscured displacements as an additional top. See Fig. 17 for perspective conformational drawings. Bottom pseudorotational normal coordinates (with symmetry species) of the Cs- and C2-symmetric transition states. The phases of the displacement amplitudes are chosen such that a mutual interconversion of both forms results. The two conformations are viewed down the CC-bonds around which the ring torsion angles - 7.3 and - 13.1° are calculated (Fig. 17). The displacement components perpendicular to the drawing plane are comparatively small. - See text for further details.

Figure 2. History of the ring torsion angle C1-C2-C3-C4 calculated from a molecular dynamics simulation of the motions of an a-D-glucopyranose molecule in vacuum which began in the C conformation and which subsequently underwent a transition to a twist-boat conformation. (Reproduced from Ref. 9. Copyright 1986 American Chemical Society.)...

It was straightforward to apply the TRMC technique to study on-chain charge transport to ladder-type poly-phenylene (LPPP) systems because covalent bridging between the phenylene rings planarizes the chain skeleton, eliminates ring torsions, and reduces static disorder. One can conjecture that in these systems intra-chain motion should be mostly limited by static disorder and chain ends. To confirm this... 

Molecules without Strong Ring Torsional Constraints 698... 

The above discussion provides a background for a discussion of the conformations of various azocanes, oxocanes, thiocanes and related compounds which lack strong ring torsional constraints. 

Figure 2 Conformation of 1,3,5,7-tetroxocane. The filled-in circles are the oxygen atoms. Bond lengths (A), internal and ring torsional angles for the crown (C2 ) are shown...

Finally, 1,2,5,6-tetrathiocanes seem to prefer the twist-boat-chair conformation (82TL3231,69AX(B)2il4). The ring torsional angles in the present compound are given in (443). 

The ring torsional angles of the amide and O-protonated amide moieties in these structures are close to zero and the C(O)—N bond length is shorter in the protonated lactam (445) (1.298 A) than it is in the lactam itself (444) (1.337 A), as expected from the dominant resonance structures in these two compounds. The room temperature 15N and 13C NMR spectra of the lactam (444) and its O-trimethylsilyl derivative have been determined but do not give much information about the solution conformation of these compounds (76JA5082, 82JMR(46)163>. 

Fig. 2. Endocyclic bond and torsional angles in heterocycles.33 (Within rings endocyclic bond angles. Outside rings torsional angles subtended by ring bonds.)...

The geometry of the pyranoid rings of these compounds is that of a regular chair, as indicated by the Cremer-Pople69-70 puckering parameters (see Table I) and the ring-torsion angles. The inclination of the... 

Prokaryotic cells, definition of 2 Proline (Pro, P) 52s in helices 69 reductases 753, 755 Proline rings, torsion angles 62 Prontosil 473s Proofreading... 

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