Bond angles protonated

Reaction energy Total energy Bond angle Bond length Atomization energy Proton affinity EA IP... 

Kashiwagi et al.10) determined the second moment anisotropy for the one-way drawn polyethylene terephthalate sheets discussed above. The three lattice sums S00, S2q and S4o were calculated from the crystal structure determination of Daubeny et al., the proton positions being calculated on the basis of known bond angles and lengths. The isotropic lattice sum S00 was adjusted to a value consistent with the measured isotropic second moment of 10.3G2. The values for P200, P220 etc. were then used to predict the optical anisotropy. The predicted refractive indices for the sheets of draw ratio 2 1 and 2.5 1 are shown in Fig. 10, together with the experimental... 

Bond angles and lengths obtained from ab initio calculations on 1,2,3-thiadiazole 1 are presented in Table 1 <1991JOM309> and can be compared to values for 4-phenyl-l,2,3-thiadiazole 10 obtained by X-ray diffraction (Section 5.07.3.1). kb initio calculations were also carried out for the ring protonated at N-2 and N-3. These calculations reveal that N-2 is the preferred site of protonation by almost 9kcalmol 1. This parallels the preferred site of metal coordination to 1,2,3-thiadiazoles found in several studies <1996CHEC-II(4)289>. 

Finally, a good correlation also exists between the distortion induced by protonation, as evident from both the apical displacement of the Re(V) center from the equatorial cyano-carbon plane as well as the bond angle (O-Re-CN), deviating significantly from the ideal 90° as in the symmetrical dioxo complex, see Table I. 

Geminal coupling. In case of protons attached to the same carbon atom having different chemical environment, the value of J depends upon the bond angle and it can have any sign. 

The discussion above has been more or less empirical and descriptive. However, considerable effort has been made to interpret 3-SCS on a more physical basis. Electric-field effects (71-75) were invoked to explain signal shifts of 3-carbon atoms induced by protonation of amines (157,158) (cf. Section II-B-3). This approach was later extended to other functionalities by Schneider and coworkers, who assumed that the SEF component (E2) rather than inductive properties of the substituents should be responsible for 3-SCS (113). They found fairly linear correlations of 3-SCS(X ) and 3-SCS(X ) in cyclohexyl derivatives (76) and attributed the difference between these for a given X to a widening of the C -Cp-Cv bond angle by 2.2° in the axial conformer (114,159). The decrease of 3-SCS in the order primary Cp —> secondary Cp — tertiary Cp — quaternary Cp was explained by electron-charge polarization in the Cp-C" bond(s) induced by the LEF component of the C -X dipole, which is already of significance at this distance, though ( 2) still dominates (160). Such an electron flow toward the 3 carbon is expected to be much more pronounced in C-C than in C-H bonds because of the polarizability difference (aCH = 0.79 acc = 1.12) (150,151,160). 

Dimensions Bond length, Proton location, / a-h Bond angle, L AHB X-Ray or neutron diffraction... 

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