On the synthesis of siloxanes: XXI. Verification of inductive and steric substituent constants for siloxy groups by reaction of triorganylchlorosilanes and chlorosiloxanes with lithium silanolates and lithium isopropylate

Abstract

In order to verify the substituent constants for siloxy groups determined previously, kinetic studies have been made of the reactions of triorganylchlorosilanes and monochlorosiloxanes with lithium silanolates and lithium isopropylate. Relative rate constants were determined by turbidimetric measurements. Comparison of these values with those determined by means of 1H-NMR spectroscopy shows that the easily performed turbidimetry is a suitable method. Initially the steric (δ) and inductive (ϱ) reaction constants for the reactions were determined with triorganylchlorosilanes, then the chlorosiloxanes were investigated kinetically. The chlorosiloxanes reacted up to 10 times faster than expected from the substituent constants we previously determined, and so we conclude that the inductive effect of the siloxy groups can vary when the charge at the reaction centre is changed.