Conformational analysis of some substituted silatranyl-carboxylic acids produced by computational study and NMR spectroscopy

The structures of four silatrane compounds, silatranyl-carboxylic acid and its derivatives (I, II, III, IV), are studied with molecular mechanics and NMR methods. The geometrical conformations of the molecules are calculated using full geometry optimization methods with MM2 and CNDO/2. The conformations obtained are in agreement with results in the literature and with our X-ray and NMR experiments. However, there are some differences between the solid state, gas phase, and solution structures. The influence of the substituents (-COOH, -CH3, -CH=CH2, -CH3) is discussed. It has been found that substitution by the carboxyl group in the silatrane framework plays a more important role in influencing the transannular structure than does substitution in the equatorial position. The calculated and experimental results are presented and discussed in detail.