Optical isomerization

The isomeric optically active substituted ammonium salts which have been reported by organic chemists are not readily explained by an ammonium theory such as has been wrongly assumed to have been established by the experiments of V. Meyer and M. T. Lecco—vide supra. J. C. Cain argued from the above hypothesis of the constitution of the ammonium compounds that the optical activity is the result of a similar spatial configuration as that assumed for the carbon compounds where the quadrivalent nucleus, say NCI", instead of quadrivalent carbon, is at the centre of a tetrahedron so that... 

Structural-, positional-, stereo-isomerism (optical and geometric) in aliphatic hydrocarbon systems. 

Isomerism, optical activity and liquid crystalline materials exhibit intersting photophysical features where luminescence is often a valuable probe. Fluorescence analysis of thermotropic biphenyl liquid crystalline polyesters has shown a... 

The stereochemistry of products relative to starting materials can give important clues to the structure of the transition state. The stereochemistry of molecules gives rise to two types of isomerism optical isomerism (cnantiomcrismjand geometrical isomerism. 

On being heated with methanolic sulfuric acid, dehydro-secovitexin gives three products D-glyceraldehyde dimethyl acetal and two isomeric, optically active, crystalline substances. A, Ci8Hi206(0Me)2, m. p. 360°, and B, dec. 188-190°. 

Willstatter and Foumeau (118) and found that their product was optically inactive. The loss of activity may have been inherent in the method of dehydration. A product could have been produced which would equilibrate between XXI and the structure XXIa, in which the second asymmetric carbon would also be destroyed. Hydrogenation of anhydrolupinine (121) over palladium on calcium carbonate according to the method of Bartholomaus and Schaumann (122) gave two isomeric, optically inactive lupinanes (XV), C10H19N, separated by the fractional crystallization of their picrates from methanol a-lupinane picrate, m.p. 187° j8-lupinane picrate, m.p. 163°. Karrer and Vogt (123) were able... 

The second type of stereoisomerism listed in Figure 23.19 is optical isomerism. Optical isomers, called enantiomers, are mirror images that cannot be superimposed on each other. They bear the same resemblance to each other that your left hand bears to your right hand. If you look at your left hand in a mirror, the image is identical to your right hand ( Figure 23.22). No matter how hard you try, however, you cannot... 

To observe particular rotational isomeric states, the method must be much more rapid than the rate of conformational isomerization. Optical methods such as absorption spectroscopy or light-scattering spectroscopy provide a short-time probe of the molecular conformation. If the electronic states of the molecule are strongly coupled to the backbone conformation, the ultraviolet or visible spectrum of the molecule can be used to study the conformational composition. The vibrational states of macromolecules are often coupled to the backbone conformation. The frequencies of molecular vibrations can be determined by infrared absorption spectroscopy and Raman scattering spectroscopy. The basic principles of vibrational spectres-... 

In a similar way, racemic 3-substituted cyclohexanones 121 were reacted with the anion of the chiral phosphoamidate reagent 18a to give two isomeric optically active alkenes, that is (S, ) and (i , Z)-alkenes possessing the opposite absolute configuration at the homoallylic carbon centers, with high enantiomeric excess [55]. 

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