A conformational study of 1-bromo-2-chloroethane in zeolites.

The conformational properties of 1-bromo-2-chloroethane (BCE) in several representative zeolites including silicalite-1, siliceous Y (Si-Y), Na-Y, and zeolite L have been investigated by FT-Raman spectroscopy in combination with thermogravimetric analysis. The results indicate that the conformational and dynamic behavior of BCE inside a zeoltic host is strongly influenced by several factors such as the framework topology, the Si/Al ratio, and the nature and the locations of charge-balancing cations. For siliceous zeolites (silicalite-1 and Si-Y), the anti population of BCE increases significantly relative to pure liquid upon initial loading at room temperature. Interestingly, when lowering temperature, the anti population of BCE in silicalite-1 continues to increase, but the conformational equilibrium of BCE inside Si-Y shifts to the gauche conformer. Zeolite L and Na-Y with extra-framework cations show an almost exclusive preference for the gauche mode of the BCE molecule at room temperature, and the conformational population does not change significantly at low temperatures.