Selenium substitution

Pigment color is determined by the ratio of Cd, and Zn or Hg if present, to S and Se in the product and can be changed all the way from primrose to maroon. Mercury substitution for cadmium yields (Cd, Hg)S pigments with ted and maroon shades similar to those obtained with selenium substitution. The Cadmium Association provides the simple diagram given in Figure 5 showing the color and composition correlation. 

The substitution of an a-oxygen by an a-sulfur or an a-selenium results in a decrease in ks/kp for partitioning of oxocarbenium ions between addition of solvent and deprotonation. The largest effect is observed for the a-selenium substitution. These changes are probably the result of several different effects on carbocation reactivity, each of which contributes to the observed substituent effect on kjkp. 

Glycoside Synthesis from 1-Sulfur/Selenium-Substituted Derivatives... 

---