Conformational diphenylmethane

In comparison, both the free ligand and the dinuclear Cu(I) cryptate of an analogous macrobicyclic structure possessing a diphenylmethane group as a central unit display only two resonances for the CH2CH2 fragment, as is the case here only for the complexes 91 and 92. This points to the special conformation features of the free macrobicycles 89 and 90. 

Calix[4]arenes are composed of repeating 3,3 -diphenylmethane units, useful for designing a boronic acid-based glucose receptor.1421 Accordingly, if two boronic acids are introduced into the para positions of the proximal phenyl units, the compound will include the basic structure of 23 within the calix[4]arene skeleton. It is known that calix[4]arenes may change their conformation in response to metal binding.176,771 This... 

Our procedure in predicting poly(MDI-PDO and poly(MDI-EDO) conformations has been to take the extended minimum energy conformation for the diphenylmethane diurethane section (Xi = -90°, l=-60°, 2 = -60°, X2 = +90°) and to look at possible conformations of the diol sections, comparing their relative energies and fiber repeats. (12) These conformations are defined by the torsion angles (i)3 and [for poly(MDI-PDO) only] as shown... 

Similar problems arise when we deal with possible reference structures that can be interconverted by internal rotations. Consider, for example, the diphenylmethane molecule (Scheme 2.2), where conformations with the planes of both phenyl groups either parallel or perpendicular to the C-CH2-C plane have C2V symmetry. Rotation of a phenyl group through 71 produces a conformation that is isometric with the initial one, but such a rotation is not a symmetry operation of the C2V point group. However, it is clear that such operations have to be included in the group of all operations that leave the reference structure invariant. We shall not attempt to review here the work that has been done on the classification of such symmetry operations on non-rigid molecules [23], nor the controversies that have ensued from it. Instead we present four representative examples of such molecules. 

An arbitrary conformation of the diphenylmethane molecule can be characterized by the torsional coordinates o)a and cub with specific components and 4>i (Figure 2.11). We define the zero value of when C(2A) eclipses the ipso-carbon C(1B), and similarly for (pi, increasing torsion angle corresponds to clockwise rotation of the phenyl group in question, viewed along the bond from the central atom to the phenyl group. 

Fig. 2.11. Isometric conformations of the diphenylmethane molecule. The conformations 1, 2, 3 and 4 can be transformed into one another by point-group symmetry operations that leave the central frame unaltered or by appropriate rotations of the phenyl groups...

A pattern of this kind, a conformational map [27], containing a set of 16 points corresponding to the 16 isometric conformations of diphenylmethane is shown in Figure 2.12. A primitive unit cell containing four equivalent points may be defined by 0Bspecial positions (fixed points) are the diagonal... 

Fig. 2.12. Conformational map of diphenylmethane. The 16 equivalent positions (open circles) are images of the 16 isometric conformations with different values of the two torsion angles. The unit cell shown is non-primitive, the primitive iattice having translation distances of n along Wa d along Wg. The plane group is cmm, with translation vectors y, = coa +Wb> 2 = Wa-Wb- The general positions of this plane group are images of arbitrary conformations, the special positions images of conformations with point-group symmetry...

This leads to the appearance of both anti and syn rotational conformations, which coexist in the DBDI based PU macromolecules, (Fig. 2.4-2.6). As a result, in this latter case the PU macromolecules can adopt a more compact packing which enhances significantly the ability to order in crystalline structures involving predominantly the anti form [60]. Shown in Fig. 2.4 and 2.5 are the extended linear anti and contorted syn DBDI positions as compared to the conventional rigid 4,4-diphenylmethane diisocyanate (MDI) non-crystallizing (Fig. 2.6). 

To get hosts capable of binding aliphatic guests, novel cyclophanes (29, 30) having naphthylphenylmethane skeletons instead of diphenylmethane skeletons were designed based on CPK model studies [12]. In their most expanded conformations, these hosts are expected to provide wider cavities of about 5.4 A in their shorter width of their open ends. 

Diphenylmethane exhibits two aromatic rings, which achieve coplanarity in the highest energy conformation. Explain. 

When the two phenyl rings of the diphenylmethane moiety of adiphenine are linked together in the form of a rigid fluorene group as in pavatrine hydrochloride (I), the association pattern no longer conforms to that of a monodisperse micellar system [22]. The concentration dependence of the light-scattering intensity of pavatrine exhibits no such inflection as that detected in the curve of adiphenine (Fig. 4.8) and cannot be simulated by the mass-action theory. 

Cycloalkylation of benzene with 2,2 -bis(hydroxymethyl)diphenylmethane in sulphuric acid gives a good yield of (37), which is shown by n.m.r. spectroscopy to have a rigid crown conformation. ... 

This steric interaction is very similar to the steric interaction in diphenylmethane, causing it to adopt a non-coplanar conformation, as seen in the Medically Speaking application at the end of section 18.5 (The Development of Non-Sedating Antihistamines). 

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