FOLDING OF METHYLENE GROUPS IN LINEAR GLUTARAMIDE ANALOGS

We have synthetized and solved by X-ray diffraction the crystalline structure of the compound N,N'-dipropylglutaramide. The conformational preferences ''in vacuo'' of the model molecule N,N'-dimethylglutaramide have also been studied using quantum mechanical calculations at the HF/6-31G*, HF/6-311G**, and MP2/6-31G levels. Furthermore, the effect of water on the stability of the different conformations was modeled. The results indicate that the TTGGTT conformation is favored for the glutaramide analogue. Finally, quantum mechanical calculations on N,N'-dimethylsuccinamide at the HF/6-31G* level provide an explanation of the folded conformation observed in crystal succinamide and adipamide units. These results contrast with the all-trans conformation expected in polymethylenic segments.