Ring twisting

This is in strong contrast to the ring twisting observed for the triphenylmethanide anions with twist angles in the range of 30°. 

Following the recently developed energy minimisation method described by M.U. Schmidt [2], for the first time three dimensional crystal structure determinations were carried out with P.Y.13 and P.Y.14 [3]. The studies showed the molecules to be planar with the terminal phenyl rings twisted by 4-10° with respect to the acetoacetyl fragments, the degree of planarity of P.Y.14 found to be a little lower than that of P.Y.13. 

X-ray diffraction analyses revealed a practically planar crystal structure of diphenyl-DPP with the phenyl rings twisted by only 7° out of the plane of the... 

The trioxolane ring twists in order to maximize overlap of oxygen lone pairs with the lone pairs prefer to lie in a staggered orientation to minimize electrostatic repulsion <93Mi 4i6-03>. 

CulI(HCor) show similar absorption spectra to those of the A-alkyl analogue, and the extra hydrogen atom is probably attached on the pyrrolic nitrogen.239 The X-ray structure of Cu(N21-MeCor) indicates the N-21 atom to be in an sp3 configuration and the pyrrole ring twisted out of the mean plane by 23°,240... 

To avoid the ring twisting, rotation around virtual Si-----Si (h) bond is prohibited. Table... 

The torsion potential curve of compound 175 is very similar to that of 3,3 -diethyl-2,2 -bithiophene (DE33BT) 174 obtained with the same calculations <1997CPL(275)533>. The most stable conformation is the one with the two rings twisted by 76°. The coplanar energy barriers are quite high. They are about lOkcalmoP for the 0° (anti-)-conformation and 16kcalmoP for the 180° (jy -)conformation. All these values are quite comparable with those of 174 <1997CPL(275)533>. 

Essentially the same structure was obtained for the symmetrically di-p-methoxy-substituted ion [29C (X = Y = MeO)]. On the other hand, the optimized structure of the mono-p-methoxy [29C (X,p-MeO)] has the phenyl ring twisted by 53° while the anisyl is coplanar with 0Meo —0°. This conformation is 3.3 kcal moF more stable than the doubly twisted conformation the opposite conformation with the phenyl coplanar and the anisyl twisted (0H = 0° and 0Meo > 50°) is a further 9 kcal moF less stable. 

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