Periodicity in Nuclear Magnetic Shielding

Proton-shielding parameters for the binary hydrides of the elements plotted against the atomic number t f the central atom. Explanation of symbols  

Figime 6 shows the shielding terms a, ap, and a (the resultant shielding) for the proton in the binary hydrides plotted against the atomic 

i F Shielding parameters for the binary fluorides plotted against the atomic number of the central atom—molecular species. ( )ai((calc.) (DjaiS) o)ap 8) ( ) CTp(obs.). 

As to the symmetry of the plot for a a and ap, we mentioned earlier that the effective r dependence of ap may be nearer than for distant contributions, becau of the dependence of the moment of the electron on its distance r. The plot reflects (for ap) the increase in the r term across the row of the ligand and the decrease down the group, against the tendency of (AE) to decrease across the row and increase 

Groups V and VI, is higher for the lower fluorides of the halogens or xenon a comparative study of Cornwell effects would be of interest here. 

---