Rigid group

Since the peptide units are effectively rigid groups that are linked into a chain by covalent bonds at the Ca atoms, the only degrees of freedom they have are rotations around these bonds. Each unit can rotate around two such bonds the Ca-C and the N-Ca bonds (Figure 1.6). By convention the angle of rotation around the N-Ca bond is called phi (<[)) and the angle around the Ca-C bond from the same C atom is called psi (y). 

Mesogen constituted of bent or so-called banana-shaped molecules in which two mesogenic groups are linked through a semi-rigid group in such a way as not to be co-linear. 

When the electrons can be assigned to specific nuclei, and follow these nuclei perfectly, the density for such a rigid group can be written as... 

The label of rigid group as used here may apply to atoms or rigidly connected groups of atoms. In the former case, we obtain... 

This route to cyclic ketones was suggested by the rigid group principal .2 As expected from this rule, dialdehydes such as I, because of constraint imposed by the triple bond, undergo cycloolefination more efficiently than saturated dialdehydes. 

The distribution of chain sequence extension, calculated by using RIS models, is compared with isotropic-nematic transition characteristics for a number of thermotropic polymers comprising rigid groups connected by polymethylene spacers. The distribution depends strongly not only on the odd-even character of the number of methylene units of the spacers, but also on the specific groups (or atoms connected at the ends of polymethylene spacers. 

Table III. Derived Parameters for the Rigid Group Atoms of Rh2H4(P(iso-Pr)3)4...

Outline by means of suitable examples the significance of (i) structurally rigid groups, (ii) conformations and (iii) configuration on the design of new drugs. 

Fig. 4. a) Peralkylated semi-rigid thiourea bridging groups used in dinuclear chemistry (I, II) and possible approaches to rigid groups (III-VII). b) Distance similarities between a thiourea and diamine bridging group. 

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