Conformational and Configurational Analysis

Tormena et al studied conformational analysis of fluoroacetoxime using the solvent dependence of the IH, and 15N NMR spectra of (E)-fluoroacetoxime 

Pihlaja et a/. studied the solution-state conformational equilibria of trans-4, 7-dihydroxysoflavan-4-ol and trans-isoflavan-4-ol based on the temperature dependence of their vicinal coupling constants J(H —2a, H —3) and J(H —3, H — 4), which were compared to values calculated with DFT methods with the B3LYP functional. Several rotamers with respect to the C — 4 hydroxyl and C — 3 phenyl were calculated and the overall diequatorial-to-diaxial ratio at 298 K were assessed. 

Bassarello et a/. performed DFT calculations of the spin-spin coupling constants for the ethyl ester of the cxo-2-norbornanecarbamic acid. The obtained results were considered to be satisfactory. 

There is an extensive literature on interproton coupling over four bonds V(H, H ) in saturated and unsaturated molecules. With modern NMR instrumentation, these data are easily obtainable now but are often difficult to interpret because of their sensitivity to conformational, substituent, and ring-size effects. 

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In other substituted phosphorinanes the HNMR spectra are too complicated for a clear-cut conformational (and configurational) analysis. Even in 1-methylphosphorinane the H atoms of the 1-Me group appear as two multiplets due to coupling with the (a) and (e) H atoms of C-2 and C-6. However, the (a,a), (a,e) and (e,e)4/H-h coupling constants are too similar to allow conformational analysis by H NMR. We shall see later that 13C NMR is an excellent method for solving these problems. 

Klod, S. Kleinpeter, E. Ab initio calculation of the anisotropy effect of multiple bonds and the ring current effect of arenes—application in conformational and configurational analysis, Chem. Soc., Perkin Trans. 2 2001, 1893-1898. 

The IR and VCD spectra of a molecule are exquisitely sensitive to its three-dimensional structure, i.e., its stereochemistry. In addition, enantiomers exhibit mirror image VCD spectra. Consequently, IR and VCD spectra can be used to elucidate the conformational structure(s) of a molecule and VCD can, in addition, be used to determine its absolute configuration (AQ. In this section, we discuss the protocol by which conformational and configurational analysis is carried out, using the ab initio DFT calculational methodology described in the previous section. 

ORGANIC STEREOCHEMISTRY - covers conformation and configurational analysis, asymmetric synthesis, and stereochemistry and steric factors in organic reactions. 

Proton ( H) NMR, initially, was used for structural characterization, and use of the Karplus equation has allowed conformational and configurational analysis to be carried out on a wide range of polymers in solution (42). The advent of... 

Nilewski C, Geisser RW, Ebert M-O, Carreira EM. Conformational and configurational analysis in the study and... 

Different conformations and configurations of the ligands have different cavity sizes (see Fig. 8.5). Therefore, all possible isomers and conformations need to be taken into account. That is, with relatively complex systems a full conformational analysis is required. This is particularly difficult to do in an exhaustive way when the metal ion can adjust to adopt different geometries1891. 

In addition, the six-membered rings are both conformationally and configurationally mobile. In almost all cases at ambient temperature, the ring interconversion proves to be fast on the NMR time scale. So, in order to analyze the conformational equilibrium, this dynamic process has to be slowed down. Often the rate of ring interconversion can be obtained employing the theory of dynamic NMR spectroscopy, i.e., line shape analysis. 

Dioxaphosphorinane derivatives containing a substituent with different steric arrangement at the C5 position (529)-(532) have been prepared. Their conformations and configurations were determined by H, NMR and X-ray crystallographic techniques. Both chair-twisted-chair and chair-boat equilibra were observed in solution. X-Ray analysis revealed in one case two independent molecules per asymmetric unit, one with chair and the other one with a boat conformation (Figure 111). ... 

ANALYSIS OF CARBOHYDRATE CONFORMATION AND CONFIGURATION BY NMR - THE KEY ROLE OF THE KARPLUS EQUATION... 

From Uncaria gambier a further base could be obtained and the name gambirine (C22H28N204, mp 163-165°, [ajj, +28.6° (CHCI3)) given to it its structure is represented by CXXV (63). Conformational analysis coupled with physical measurements has been used to study the conformation and configuration of the corynantheidine-type alkaloids... 

Modern Techniques of Conformational, Structural, and Configurational Analysis... 

Circular dichroism (CD) is a chiroptical spectroscopy that measures the differential absorption of left versus right circularly polarized light. Its higher sensitivity to molecular conformation and configuration has made CD spectroscopy a more powerful tool in the structural analysis of various chiral supramolecular systems than its parent achiral absorption spectroscopies such as ultraviolet (UV), visible (vis), and infrared (IR) spectra (Figure 1). CD measurements in the UV and vis regions are the most widely... 

Analysis of vicinal proton-proton couplings for many years has remained an important source of information on the structure of organic compounds, and the number of papers where their application to establish conformation and configuration of molecules has been described is traditionally considerably larger than those where the other couplings are discussed. 

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