Stretching linearly correlated

C-nmr data have been recorded and assigned for a great number of hydantoin derivatives (24). As in the case of H-nmr, useful correlations between chemical shifts and electronic parameters have been found. For example, Hammett constants of substituents in the aromatic portion of the molecule correlate weU to chemical shifts of C-5 and C-a in 5-arylmethylenehydantoins (23). Comparison between C-nmr spectra of hydantoins and those of their conjugate bases has been used for the calculation of their piC values (12,25). N-nmr spectra of hydantoins and their thio analogues have been studied (26). The N -nmr chemical shifts show a linear correlation with the frequencies of the N—H stretching vibrations in the infrared spectra. 

On the assumption that all the reported aldehyde first ionization potentials refer to the oxygen lone-pair electrons Cook (1958) has classified the effect of substituents into two classes, A and B, according to whether inductive or resonance effects predominate. Two different linear correlations (Fig. 14) were found between ionization potential and the carbonyl stretching frequency. Anomalies were noted for diacetyl, benzaldehyde and mesityl oxide, ascribed in the last instance to noncoplanarity interfering with resonance. It seems more likely, however, that in these cases the first ionization potential refers to 7r-electrons and higher values for the lone-pair electrons (as yet undetermined) might remove the anomalies. 

The predominance of NH-X hydrogen bonding over other types of intermolecular association is readily distinguished by the large shift in the position of the NH stretching vibration to lower frequency (compare data in Tables IV and V). A linear correlation has been... 

Electrical resistivities, especially of the 1 1 salt formed from 223b, are relatively low. In contrast to the usual experience, however, the IR nitrile stretching frequencies of these salts are not linearly correlated with the degree of charge transfer. 

The order of stabilities derived from Raman spectra appears to be UOi+ > Np02+ > Pu02+. For aqueous solutions of U01+ there is a linear correlation between the frequency of the 0=U=0 symmetric stretch (i cm-1) and the average number of ligands so that the stoichiometries in solutions can be estimated. Complex formation leads to weakening of the U02+ axial bonds in the order OH" > CO " > C2O4" > F" > SO " and this order reflects the corresponding decrease in stability constants (log /3).4 The unstable UO2 ion disproportionates as follows ... 

The frequency shift Av = v(OH) — v(OH O), where v(OH) is the frequency of the stretching mode of the O—H bond of the isolated phenol and v(OH O) in the presence of the electron donor 0(X,)2, is very informative for this series. The quantity Av is linearly correlated with the change of enthalpy (energy of donor-acceptor bond in the H-complex) and free energy (stability of the H-complex) , as well as with the value of effective charge q on the donor centre B, which was calculated by quantum-chemical... 

Cooperativity is more obvious in the coupling constants. The values for the terminal molecules continue to diminish as the chain grows beyond the dimer level. As in the case of the D atom, the coupling constants are smaller for the molecules in the middle of the chain. The authors noted a close linear correlation between the N quadrupole coupling constants and the lengths of the pertinent H-bonds. This same property was found to correlate also with the v stretching frequencies. 

Overall, very few data are available on the solvent dependence of the CO-stretching fundamentals. Few correlations have been sufficiently well-established to be used for band assignment. It has been found, however, that if the CO-stretching frequencies of the compound Mn2(CO)jo were plotted against those of the derivatives Mn2(CO)gL2 in a series of nonpolar solvents, linear correlations were only found when fundamentals belonging to the same symmetry species were compared (259). These observations were consistent with the band assignment proposed for the derivatives, and served as a check for the correct assignment. 

---