Optical activity magnetic

Gas-phase Photoelectron Spectroscopy Electronic Spectra of Transition Metal Complexes Natural and Magnetic Optical Activity Magnetic Susceptibility Measurements. 

This sixth volume in the series of Specialist Periodical Reports deals with electronically excited states and the Magnetic Properties of inorganic compounds. Contents include Gas-phase Photoelectron Spectroscopy Electronic Spectra of Transition Metal Complexes Natural and Magnetic Optical Activity Magnetic Susceptibility Measurements. —324pp January 1980... 

Chiral-at-metal cations can themselves serve as chirality inducers. For example, optically pure Ru[(bipy)3] proved to be an excellent chiral auxihary for the stereoselective preparation of optically active 3D anionic networks [M(II)Cr(III)(oxalate)3]- n (with M = Mn, Ni), which display interesting magnetic properties. In these networks all of the metalhc centers have the same configuration, z or yl, as the template cation, as shown by CD spectroscopy and X-ray crystallography [43]. 

Exchange reactions can be sometimes investigated by the techniques of polari-metry, nuclear magnetic resonance and electron spin resonance. The optical activity method requires polarimetric measurements on the rate of racemization in mixtures of d-X (or /-X) and /-Y (or d-Y). 

Small gold clusters (<100 atoms) have become the subject of interest because of their use as building blocks of nanoscale devices and because of their quantum-size effects and novel properties such as photoluminescence, magnetism, and optical activity [427]. 

The long-wavelength, jr - n, transition is also magnetically allowed for the skewed and for the s-cis conformations, as seen by inspection of the character tables. It is therefore apparent that for the planar isomers, s-trans and s-cis, there is no optical activity allied to the jr - ji transition (as obviously expected). In fact, for the s-trans form mjt = 0, while for the s-cis /j, and m are orthogonal. In both cases the scalar product in equation 1 vanishes. 

An electric dipole operator, of importance in electronic (visible and uv) and in vibrational spectroscopy (infrared) has the same symmetry properties as Ta. Magnetic dipoles, of importance in rotational (microwave), nmr (radio frequency) and epr (microwave) spectroscopies, have an operator with symmetry properties of Ra. Raman (visible) spectra relate to polarizability and the operator has the same symmetry properties as terms such as x2, xy, etc. In the study of optically active species, that cause helical movement of charge density, the important symmetry property of a helix to note, is that it corresponds to simultaneous translation and rotation. Optically active molecules must therefore have a symmetry such that Ta and Ra (a = x, y, z) transform as the same i.r. It only occurs for molecules with an alternating or improper rotation axis, Sn. 

A particularly useful probe of remote-substituent influences is provided by optical rotatory dispersion (ORD),106 the frequency-dependent optical activity of chiral molecules. The quantum-mechanical theory of optical activity, as developed by Rosenfeld,107 establishes that the rotatory strength R0k ol a o —> k spectroscopic transition is proportional to the scalar product of electric dipole (/lei) and magnetic dipole (m,rag) transition amplitudes,... 

Nonlinear Optical Activity and Magnetic Dipole Contributions... 

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. 

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