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ions. In the former instances, the SnI mechanism predominates, and the rate-determining step is the formation of a carbonium ion which then reacts readily with an anion to form the product. By such a mechanism, it is evident why cellulose, with its very weakly ionized hydioxyl groups, does not react with the epoxides to form cellulosic ethers readily in the presence of large concentrations of hydrogen ions.However, if the Sn2 mechanism predominates, as in the instance of low concentrations of hydrogen ions and in the presence of Zn+2 ions, the cellulose molecules can compete with water or other solvent molecules in a bimolecular reaction with the conjugate acid of the epoxide in the slow rate-determining step.

think, be fairly summarized by the statement that if unambiguous reaction rate constants can be found, then the quotient of the experimentally determined constants will give the equilibrium constant.Without committing them to my views, I wish to thank Drs. Wendell Forst, Benjamin Widom, John Ross, and H. 0. Pritchard for discussions and correspondence. In the light of their criticisms, the presentation has been considerably revised.

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