The Rotatory Dispersion and Stereochemistry of Organic Compounds. XIV. Nitrobenzylidene Derivatives of Diethyl d-Tartrate

Abstract

Abstract Anomalous optical rotation has been observed not only with the ortho-nitrobenzylidene derivative of diethyl d-tartrate (Tsuzuki, Bull. Chem. Soc. Japan, 14, 35 (1939); Sci. Pap. I. P. C. Res. (Tokyo), 35, 425, 466 (1939)), but also with some acetylated ortho-nitrophenyl glycosides of the β-type (Capon et al., J. Chem. Soc., 1961, 5172; Montgomery et al., J. Am. Chem. Soc, 64. 690 (1942); Snyder et al., ibid., 75, 1758 (1953); Tsuzuki et al., Bull. Chem. Soc. Japan, 40, 1208 (1967)). To investigate this anomalous effect of the ortho-nitro group the authors have made rotatory dispersion studies on several derivatives of diethyl d-tartrate as well as its alkylidene derivatives. Of these compounds examined, the compound (I) with a nitro group in the ortho-position of the phenyl group shows a positive Cotton effect at about 340 mμ, and it has been found that the nitrophenyl group is optically active. Furthermore, in order to inquire into this anomaly the authors have observed the CD, UV and NMR spectra of these compounds, from which it is concluded that the conformations of the acetal rings of all the compounds are nearly equal, and the anomalous dispersion of the compound I at about 340 mμ, is assumed to be due to the n→π* transition of the nitro group with a slight shoulder appearing at 325 to 350 mμ. In view of these facts it is considered that the ortho-nitro group is twisted from the plane of the benzene ring caused by the steric hindrance of the bulky acetal ring.