Gauche rotamers

Fig. 1 (a) Comparison of measured values of for two P-phospholyl-NHPs at different temperatures in solution (data denoted as squares or diamonds, respectively solid lines represent fits of the temperature dependent variation) with values measured in the solid state (dashed horizontal lines). (b) Explanation of the observed variation in solution as a consequence of a dynamic equilibrium between trans- and gauche-rotamers. (Data from [45])... 

C in Figure 7. The results of the quantitative analysis are included in Table III. Most notable in Figure 4 and Table III are the suppression of gauche rotamer formation at 49°C at the 6(6 ) position, as shown by the relative weakness of the jt features at... 

The PES for rotation around the C—C bond of 58, M=Si, Ge (Figure 18) shows two minima the s-trans and the gauche, while the s-cis structure is a saddle point that connects two gauche enantiomers. The gauche rotamer is by ca 4333 and 3 kcal mol-1335 for 58, M = Si, Ge, respectively, less stable than the s-trans rotamer, an energy difference very similar to that in 1,3-butadiene. However, the rotation barrier about the central C—C bond in 58, M = Si and Ge, of ca 10-11 and 9.5 kcalmol-1, respectively, is... 

Figure 4-21. Chloropropene isomerization the changes in the selected interatomic distances (a) and the torsions (b) along the IRC and the 300K MD simulation. The gauche-rotamer structure, formation of which is responsible for deviation from IRP is shown in panel c...

In the reaction between anti-W2Cl2(NEt2) and alkyllithium reagents LiR (2 equiv), substitution of Cl-by-R occurs with retention of configuration (18). Kinetically anti-WgRgfNEtg) is formed which then isomerizes to a mixture of anti and gauche rotamers, with the latter being the favored rotamer. This substitution reaction can be viewed as an example of an S 2 process in... 

Many of the trisilanes exist as mixtures of rotational rotamers, as can be proved with variable temperature Raman spectroscopy. As an example Fig. 2 shows the v(SiCl) region of the Raman spectrum of ClMe2SiSiMe2SiMe3, which exists as a mixture of anti- and gauche- rotamers at room temperature. 

Recently, the spectrum of Me2SbSbMc2 has been recorded and it has been found to be very similar to that of tetramethyldiarsine. Lone-pair ionizations from the trans rotamer occur at 7.72 and 9.4 eV while the small peak corresponding to the gauche rotamer appears at 8.65 eV. The rotameric composition was determined on the basis of band areas as 88% trans and 12% gauche, just as in the case of Me2AsAsMc2. The band arising from the Sb—Sb bonding a orbital has been tentatively placed at 9.08 eV. 

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