Specific rotation Spectroscopy

An interesting method for the estimation of optical purity of sulfoxides, which consists of the combination of chemical methods with NMR spectroscopy, was elaborated by Mislow and Raban (241). The optical purity is usually determined by the conversion of a mixture of enantiomers into a mixture of diastereomers, the ratio of which may be easily determined by NMR spectroscopy. In contrast to this, Mislow and Raban used as starting material for the synthesis of enantiomeric sulfoxides a diastereomeric mixture of pinacolyl p-toluenesulfinates 210. The ratio of the starting sulfinates 210 was 60.5 39.5, as evidenced by the H NMR spectrum. Since the Grignard reaction occurs with full stereospecificity, the ratio of enantiomers of the sulfoxide formed is expected to be almost identical to that of 210. This corresponds to a calculated optical purity of the sulfoxide of 20%. In this way the specific rotations of other alkyl or aryl p-tolyl sulfoxides can conveniently be determined. 

The primary significance of microwave spectroscopy for chemistry is in determination of molecular structure. Assignment of microwave spectral lines to transitions between specific rotational levels allows determination of the rotational constants A0, B0, and C0, and the corresponding moments of inertia. The moments of inertia are dependent on the molecular bond distances and bond angles. 

Carbohydrates in nature are optically active and polarimetry is widely used in establishing their structure. Measurement of the specific rotation gives information about the linkage type (a or (3 form) and is also used to follow mutarotation. Nuclear magnetic resonance spectroscopy (NMR) can be used to differentiate between the anomeric protons in the a- or /3-pyranose and furanose anomers and their proportions can be measured from the respective peak areas. 

The spectroscopy data of synthetic 181, as well as the specific rotation, were found to be identical with that reported for the natural product. The corresponding acetate of synthetic 181, obtained by direct acylation, was identical with the natural product in all respects. Therefore, we could conclude that the absolute configuration of C-11, C-12 of 181 to be (115,125). 

Solvents, classification, 22 Solvolysis, 123, 126 Specific rotation, 70 Spectroscopy, infiared, 233/T mass, 247 ... 

The relevance of C-H- - -tt interactions in many supramolecular systems has made them the subject of specific monographies [6]. In these interactions the acceptor is constituted by the region where the ir-electrons are located (double, triple bonds, or aromatic ir-rings). The best known ir-acceptors are phenyl rings, double and triple C-C bonds, cyano groups, and pyridyl rings. The hydrogen bonded nature of the C(sp)-H- n interactions in the acetylene acetylene [102] and HCN-acetylene [103] complexes has been established by a combination of experimental techniques (gas-phase rotational spectroscopy... 

Contributions which do not depend on the rotational states are not included in Eq. (IV.59) since they would cancel in pure rotational transitions and are thus of no immediate interest as far as rotational spectroscopy is concerned. Although we will not discuss in detail all neglected terms, we will examine some specific cases. For this purpose we arbitrarily pick a contribution which stems from Eqs. (IV.56b) and (IV.56g) and we will specialize to the case where y=y =y"= . Using the symbol Nq for this neglected contribution, we get ... 

Excitation of the outer ns electron of the M atom occurs easily and emission spectra are readily observed. We have aheady described the use of the sodium D-line in the emission spectrum of atomic Na for specific rotation measurements (see Section 3.8). When the salt of an alkali metal is treated with concentrated HCl (giving a volatile metal chloride) and is heated strongly in the non-luminous Bunsen flame, a characteristic flame colour is observed (Li, crimson Na, yellow K, lilac Rb, red-violet Cs, blue) and this flame test is used in qualitative analysis to identify the M ion. In quantitative analysis, use is made of the characteristic atomic spectrum in flame photometry or atomic absorption spectroscopy. 

---