Magnetic optical rotation

From another point of view MCD can be regarded as the absorptive counterpart of magnetic optical rotation dispersion (MORD) the well-known Faraday effect. This is the reason why in the past the spectra were given in the units of natural optical rotation per magnetic field... 

Indeed, only the difference is significant. This difference is drastically increased by applying a magnetic field this is the basis of magnetic optical rotation and MCD. 

Faraday found experimentally that all substances show this effect in presence of a magnetic field (Schatz and Me Caffery, 1969), leading to Magnetic optical rotation dispersion (MORD) and Magnetic circular dichroism (MCD) (Caldwell and Eyring, 1976 Dawber, 1964 Foss and Mccarvil, 1965 Schatz et al., 1978 Thome, 1977). Experimentally however, ORD and MORD were never measured extensively contrary to CD and MCD. 

Although the magnetic-field technique is commonly used in magnetic resonance and spectroscopy (like the Zeeman effect, magnetic optical rotation, and magnetic circular dichroism), its application to directly probing the dynamic processes of the excited electronic states of atoms and molecules... 

Parkinson, W. A., Oddershede, J. (1997). Response function analysis of magnetic optical rotation. International Journal of Quantum Chemistry, 64, 599. 

The melting points, optical rotations, and uv spectral data for selected prostanoids are provided in Table 1. Additional physical properties for the primary PGs have been summarized in the Hterature and the physical methods have been reviewed (47). The molecular conformations of PGE2 and PGA have been determined in the soHd state by x-ray diffraction, and special H and nuclear magnetic resonance (nmr) spectral studies of several PGs have been reported (11,48—53). Mass spectral data have also been compiled (54) (see Mass spectrometry Spectroscopy). 

Specific optical rotation values, [a], for starch pastes range from 180 to 220° (5), but for pure amylose and amylopectin fractions [a] is 200°. The stmcture of amylose has been estabUshed by use of x-ray diffraction and infrared spectroscopy (23). The latter analysis shows that the proposed stmcture (23) is consistent with the proposed ground-state conformation of the monomer D-glucopyranosyl units. Intramolecular bonding in amylose has also been investigated with nuclear magnetic resonance (nmr) spectroscopy (24). 

Other physical methods were also applied to the elucidation of the isomerism of diazocyanides, e. g., determination of diamagnetic susceptibility, the Faraday effect (optical rotation in a magnetic field), and electronic and infrared spectra. Hantzsch and Schulze measured ultraviolet spectra at a remarkably early date (1895 a). Unfortunately, their results and later work (Le Fevre and Wilson, 1949 Freeman and Le Fevre, 1950) did not allow unambiguous conclusions, except perhaps the observation that the molar extinction coefficients of the band at lowest frequency are consistently larger in all types of (i -compounds Ar — N2 - X than in the corresponding (Z)-iso-mers (Zollinger, 1961, p. 62). 

Rotating anode, conventional optics Rotating anode, Gobel mirror optics Synchrotron, bending magnet (DORIS, A2) Synchrotron, insertion device (ESRF, ID2)... 

Figure 9.2 Quantitative description of optical rotation. A vertically polarized electric field Em is incident on chiral system and induces vertically directed dipole moment i and magnetic moment m. Both act as sources of radiation, p, giving rise to vertically polarized field, m giving rise to horizontally polarized field. Sum of both fields is a new field E0ut with polarization rotated over angle 0.

Enantiomers have identical chemical and physical properties in the absence of an external chiral influence. This means that 2 and 3 have the same melting point, solubility, chromatographic retention time, infrared spectroscopy (IR), and nuclear magnetic resonance (NMR) spectra. However, there is one property in which chiral compounds differ from achiral compounds and in which enantiomers differ from each other. This property is the direction in which they rotate plane-polarized light, and this is called optical activity or optical rotation. Optical rotation can be interpreted as the outcome of interaction between an enantiomeric compound and polarized light. Thus, enantiomer 3, which rotates plane-polarized light in a clockwise direction, is described as (+)-lactic acid, while enantiomer 2, which has an equal and opposite rotation under the same conditions, is described as (—)-lactic acid. 

Structural information at the molecular level can be extracted using a number of experimental techniques which include, but are not restricted to, optical rotation, infra-red and ultra-violet spectroscopy, nuclear magnetic resonance in the solid state and in solution, diffraction using electrons, neutrons or x-rays. Not all of them, however, are capable of yielding structural details to the same desirable extent. By far, experience shows that x-ray fiber diffraction (2), in conjunction with computer model building, is the most powerful tool which enables to establish the spatial arrangement of atoms in polymer molecules. 

In this paper, we first briefly recall the main features of the collagen molecule, then we describe the structure of the gels, using different experimental techniques (optical rotation (O.R.), electron microscopy, proton nuclear magnetic resonance (N.M.R.)) for different thermal treatments. A phenomenological and a microscopic interpretation of the mechanisms of gel formation is suggested. 

The imaginary and real parts of the frequency-dependent response of the electric dipole moment to a magnetic field ((3) are responsible for optical rotation and CD, respectively, while the imaginary and real parts of the first-order correction to the... 

The first attempt to formulate a theory of optical rotation in terms of the general equations of wave motion was made by MacCullagh17). His theory was extensively developed on the basis of Maxwell s electromagnetic theory. Kuhn 18) showed that the molecular parameters of optical rotation were elucidated in terms of molecular polarizability (J connecting the electric moment p of the molecule, the time-derivative of the magnetic radiation field //, and the magnetic moment m with the time-derivative of the electric radiation field E as follows ... 

Initially, stereospecific analyses were done by Pitas et al. (1967) on whole milk fat and by Breckenridge and Kuksis (1968) on a molecular distillate of butter oil. They indicated that the short chain acids were selectively associated with the sn-3 position. In the butter oil distillate, over 90% of the TGs contained two long-chain and one short-chain fatty acids. This asymmetry has been confirmed by the observation of a small optical rotation of the TGs (Anderson et al. 1970), by proton magnetic spectroscopy (Bus et al. 1976), and by nuclear magnetic resonance spectroscopy (Pfeffer et al. 1977). Pfeffer et al. found 10.3 M% 4 0 (butyric) in the oil and determined that 97% of the acid was in the sn-3 position. It is worth noting that the analysis was done without alteration or fractionation of the oil. 

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