Substituted alkanes conformation

The most stable conformation of a substituted alkane is generally a staggered one in which large groups have an anti relationship. The least stable conformation is generally an eclipsed one in which large groups are as close as possible. 

Many applications have been reported in the field of biomolecular NMR spectroscopy which use RDCs for the refinement of three-dimensional structures. The approach is quite powerful and can also be applied to smaller molecules whenever the conformation of a molecule is important, as for example in the case of rational drug design. Traditionally, NMR in liquid crystals is applied on a multitude of small organic compounds to obtain their fully characterized structure. Most examples are measured on all kinds of aromatic systems as reported in refs. 204—212 other recent examples deal with substituted alkanes, aldehydes216,217 or bridged systems like norbomadiene.218 In general, these very detailed studies can be applied to molecules with up to 12 protons. 

This enantiomer would be dextro or levo as the rotational contributions of X and Y differ and would, of course, be zero if the two groups were identical. The term derives from the fact that the mol fraction of each conformer would be n = n = 0.5. Conformational rotatory powers, relative to Y = CH3, were assigned (Table 5) to give reasonable fits to the data for various 2-substituted alkanes (Table 6). The values in Table 5 decrease in accord with the square root of the atomic refractions of the atoms (a measure of polarizability). 

In order to cope with the more complex situation obtaining in the alkanes and substituted alkanes, a further all-or-nothing rule was adopted, namely, that the five-atom meso digauche conformation 21 would also be forbidden . The steric strains occurring here would resemble those present in diaxial cis-1,3-dimethylcyclohexane (but see Section III.B.2.c). With conformations 20c and 21 forbidden , the 27 possible chain conformers of 3-methylhexane reduce to six allowed forms which are considered to be... 

Bicyclopentyl shows a strong preference for the conformation with the highlighted hydrogens anti. Rationalize this result within the context of the conformational preferences of other, similarly substituted alkanes. 

Increasing the chain length of the alkanes, conformational analysis of a series of methyl substituted hexanes indicates that the important potential energy profiles can be identified with those bonds which contain the methyl substituent. This has important consequences for polymers. The theoretical rotational isomeric potential profile for 2-methylhexane is shown in Figure 3.8. 

Conformational preference of phenyl-substituted alkanes, alkenes, and alkynes guests and their piperidine analogs shown in Scheme 3.142 within the cavity of octaacid bis-cavitand caging ligand 473 has been studied in... 

Name an Alkane Using the lUPAC System 122 Name a Cycloalkane Using the lUPAC System 126 Draw a Newman Projection 132 Draw the Chair Form of Cyclohexane 140 Draw the Two Conformations for a Substituted Cyclohexane 143 Draw Two Conformations for a Disubstimted Cyclohexane 146 Stereochemistry... 

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... 

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