Double minima

Single crystal Cu-ENDOR spectra of Cu(acac)2 have been studied by Kita et al.158) up to 100 MHz. The ENDOR transitions of the isotopes 63Cu and 65Cu are found to be well separated for most orientations of Bq. The angular dependence of some Cu-ENDOR frequencies shows pronounced double-minima instead of a single minimum in the region where the hf coupling is smallest. Similar rotation patterns have been observed in Co-ENDOR spectra of Co(acacen) (Fig. 43 b). 

The second isotope effect, 87 , requires the proton and deuteron to be accurately located. The distance between the equilibrium positions of the potential energy well of double minima, symmetrical hydrogen bonds, which Ichikawa calls 7 h/h defined as q — 2i o . This distance can... 

Trisubstituted carbon-centred radicals chemically appear planar as depicted in the TT-type structure 1. However, spectroscopic studies have shown that planarity holds only for methyl, which has a very shallow well for inversion with a planar energy minimum, and for delocalized radical centres like allyl or benzyl. Ethyl, isopropyl, tert-butyl and all the like have double minima for inversion but the barrier is only about 300-500 cal, so that inversion is very fast even at low temperatures. Moreover, carbon-centred radicals with electronegative substituents like alkoxyl or fluorine reinforce the non-planarity, the effect being accumulative for multi-substitutions. This is ascribed to no bonds between n electrons on the heteroatom and the bond to another substituent. The degree of bending is also increased by ring strain like in cyclopropyl and oxiranyl radicals, whereas the disubstituted carbon-centred species like vinyl or acyl are bent a radicals [21]. 

It had been anticipated that the reaction pathway for a proton transfer reaction should be characterized by a double minima in the potential surface.100 The failure of Qementi s calculation to predict a barrier along the reaction pathway for the transfer of H + from HQ to NH3 to form NHJC1-, must be accepted with some caution in view of the lack of polarizing functions on N and Cl in the basis set. This work, however, broke new ground and dementi99 includes in his paper a detailed discussion of the merits and faults to be expected for the Hartree-Fock method in the different regions of the potential surface. 

Molecular mechanics calculations and temperature-dependent CD spectra may reveal details of the conformational map not attainable by DNMR. Thus, double minima within each of the anti and syn forms were inferred from molecular mechanics calculations and were also supported by the temperature dependence of the CD spectra. Rotational strength calculations for the stable conformations predicted by the molecular mechanics calculations (or for any other arrangement) are in fair agreement with respect to both the sign and the dissymmetry factor for many of the studied compounds and may also allow for tentative assignments of absolute configuration in cases where this is not known (87JA492). 

Fig. 15 Double minima potential of the triple-proton transfer in a hydrogen-bonded...

Pathological potentials, for example, those with double minima, will not adhere to these rales. Very weak interatomic and intermolecular interactions, for example, van... 

Qualitatively, CD spectral analysis indicated that LXRa was different from the other constructs, all of which exhibited classical a-helical structure. The LXRa spectrum clearly did not contain double minima at 208 and 222 nm but instead had a more narrow trough with a minimum around 220 nm. The spectrum is very similar to that taken from a PPARa sample which we progressed to 60°C and then rescanned (data not shown). This unfolded PPARa did not exhibit ligand binding in the gel filtration assay. Also, LXRa showed heavy scattering below 220 nm. Taken altogether, the CD data suggest that recombinant LXRa as expressed does not share a similar structure with the other four constructs. 

Porphyrin complexes, as oxidation catalysts 1201, 1205,1211 Porphyrins—see also meso-Tetraphenylporphyrin reactions of 1082 Potential energy surface 3 Potentials, double-minima 371, 377 symmetrical OH stretching 382 Potential weU, shape of 349 Preconcentration, of analytical samples 930, 932, 934, 936, 942, 944-949, 955, 962-964, 971, 972, 983-987, 995 Prenylphenols, C chemical shifts for 338 Pressure transducers 851 Prestegane A 1244... 

The solid line shows the potential profile for the single graphite surface. The potential becomes deeper with decrease in the w value. The potential profile has double minima for... 

As the interaction potential at the mid point of the slitlike pore is the deepest in the pore of w < 0.6 nm and it is not seriously different from the double minima even for w > 0.6 nm, molecular potential for a molecule in the micropore can be approximated by the potential at the mid-point of the slitlike pore. The molecular potential indicates the presence of the inherent micropore of the volume of Wl for each adsorptive. Here the inherent micropore must have sufficiently strong molecular field in comparison with the thermal energy at a measuring temperature. The inherent micropore volume Wl for vapour molecules is almost equal to the micropore volume Wq obtained from N2 adsorption at 77 K (Gurvitch rule) Wl for a supercritical gas which depends on the molecule-surface interaction can be evaluated as the saturated amount of adsorption from the Langmuir plot and Wl is less than Wo in general. 

Figure 3.8 Ab initio adiabatic potential curves with double minima for the 1 >J9 states of H2 (dash-dot line). The diabatic laag2sag and (2pou)2 potentials are also plotted (dashed line). The (nl) labels on the small-i potential mimima denote the dominant ls

Another interesting feature of Europa s light scattering near opposition is the double-minima shape of the negative polarization branch (see Figure 13). This effect recently was seen in telescopic observations of Galilean satellites and some bright asteroids [29,30,36]. 

---