Dipole moment group

BOND AND GROUP DIPOLE MOMENTS Table 4.12 Bond Dipole Moments... 

All values for bond and group dipole moments in Tables 4.12 and 4.13 were obtained in benzene solutions. 

The unequal distribution of electron density in covalent bonds produces a bond dipole, the magnitude of which is expressed by the dipole moment, having the units of charge times distance. Bonds with significant bond dipoles are described as being polar. The bond and group dipole moments of some typical substituents are shown in Table 1.7. 

One center has been attributed to the central sulfur atom because it is impossible to assign it either to the S-0 bond or the methyl groups, as can be seen in Table I and Fig. 1. As expected, the main contribution to the total dipole moment of DMSO stems from the S-0 bond dipole, see third row of Table I. The methyl groups contribute only in a small way. Whereas the S-0 bond dipole increases, the methyl group dipole moments decrease upon solvation which is in accordance with the observed red-shift and blue-shift from many experiments. The increase of the DMSO dipole moment upon solvation is about 81%. This increase can only partly be explained by the 23% increase of the S-0 bond dipole. A much larger share is due to the reduction of about 35% of the methyl group. 

The chemical shifts of 1-substituted adamantanes are correlated well with substituent electronegativity 15°) as measured by a 152 or group dipole moments 153X Only the chemical shifts observed for the 7 (bridgehead) position exhibit the normal inductive order, however the chemical shifts of the 0 (adjacent methylene) and 5 (far methylene) hydrogens appear to be anisotropy controlled 150>. 

Betaines, with l,n-alkylene linking groups calculations, 60, 240 difficulties with crystallography, 60, 236 elimination reactions, 60, 246 formation, 60, 210, 211, 214-5, 216 nmr spectra, 60, 224-5 Betaines, with methylene linking group dipole moments, 60, 232, 234 formation 60, 205, 60, 210, 211, 216 nmr spectra, 60, 224-5 theoretical calculations, 60, 237 x-ray crystal structures, 60, 235-7... 

There is presently no theoretical estimate of the effect of group dipole moments when they are linked in such a way that their orientations are partially correlated. There has been a preliminary treatment of the case in which they are rigidly linked to form a net quadrupole [65g]. 

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