Alkanes optical isomerism

Optical isomerism will start becoming possible in alkanes when there are enough carbon atoms to distribute four different groups around a central carbon atom. This starts with heptane (C7H16), as in Figure 6.4.19. 

Next, we examine aliphatic hydrocarbons. First we study the nomenclature and reactions of alkanes. We examine the optical isomerism of substituted alkanes and also the properties of cycloalkanes. We then study unsaturated hydrocarbons, molecules that contain carbon-to-carbon double bonds and triple bonds. We focus on their nomenclature, properties, and geometric isomers. (24.2)... 

Constitutional Isomerism and the Physical Properties of Alkanes Chiral Molecules and Optical Isomerism Alkenes Alkynes... 

Optical isomerism. Write a structural formula for the simplest alkane... 

A special case of isomerization is the racemization of optically active compounds catalyzed, for example, by sulfuric acid or promoted A1C13. Thus, treatment of (+)-(5)-3-methylhexane at 60°C with 96% sulfuric acid yields a mixture of racemic 2- and 3-methylhexane68 (Scheme 4.4). At lower temperature (0 or 30°C), racemization occurs, but shift of the methyl group does not take place. It can be concluded that at 60°C methyl migration is faster than hydride abstraction to yield isomeric alkanes. At 0 or 30°C, hydride transfer occurs before methyl... 

Ono and Ware"" have measured the absorption, emission, and excitation spectra, the fluorescence decay times, and the quantum yields of a series of substituted diphenylmethylenes in rigid matrices at low temperatures. Acean-thrylene shows S2- So emission in hexane with a yield of 0.017 and lifetime of 4.3 ns. The low-temperature fluorescence spectra of bis-2-naphthyl-alkanes and their derivatives have been studied. Excimer formation is an activated process. The fluorescence and absorption spectra of 1,1-diphenyl-ethylenes have been analysed in some detail by Gustav and Bolke. " The S — Si transitions in trans isomers of phenylnaphthylethylenes have been assigned by picosecond absorption spectroscopy. Effects of solvent viscosity and the role of conformers in the mechanism of isomerization are elucidated. The production of non-equilibrium conformer concentrations in glassy solutions of diarylethylenes at 77 K due to restrictions imposed by the solid matrix has also been reported. Free jet excitation and emission spectra of diphenyl-butadiene show clearly the lowest excited Ag state and give a lifetime of 52.8 ns for 0-0 excitation.Electric field-induced charges in the optical... 

Acid catalysts are required for alkane isomerizations and all the reactions of this type probably involve carbonium ions. Optically active tertiary alkanes can be racemized by sulfuric acid at room temperature or by fluorosulfonic acids at -80 C. ... 

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