Homonuclear calculated from

In many cases the temperature dependence of the quadrupolar coupling constant is an indicator of dynamic processes, because the symmetry around the lithium cation is affected by motions which are fast on the NMR time scale. If the rate of these processes exceeds 1/x, the effective symmetry around the lithium cation increases and a decrease in x( Li) results. In Li MAS spectra, a broadening of the satellite transitions can be observed which eventually disappear completely if the rate of the dynamic process comes in the order of the quadrupole frequency. This behaviour was observed for the THF solvated dimer of bis(trimethylsilylamido)lithium, where the Li MAS spectrum at 353 K shows only the central transition and the sidebands caused by CSA and homonuclear Li- Li dipole coupling (Figure 27) . The simulation of the high-temperature spectrum yielded —20 ppm and 1300 Hz for these quantities, respectively. The dipole coupling agrees closely with the theoretical value of 1319 Hz calculated from the Li-Li distance of 2.4 A, which was determined by an X-ray study. 

Let us start by considering a molecule with two coupled nuclei (A and B) of the same isotope (e.g., H). There are three independent variables that describe the system completely the chemical shifts (8 or 5v) of A and B and their homonuclear coupling constant 7. The exact appearance of the NMR spectrum for this system, that is, the position and intensity of each line, can be calculated from the values of these three variables (and the operating frequency of the instrument if 8 values are used). The general solution for the two-spin system is a four-line spectrum, with each line having the position and intensity listed below ... 

Experimental studies have shown that, in practice, the effect of second-order quadrupolar interactions can produce gross deviations from a Gaussian-type decay curve, reflecting the influence of higher moments on the time evolution behavior [ 11 ]. It has been shown, however, that dipolar information can still be obtained if the analysis is restricted to the initial curvature in the limit of short dipolar evolution times (2ti<200 ps). The validity of this approach has been tested recently for homonuclear Na- Na dipole-dipole interactions in crystalline solids, for which the M2 values are readily calculable from the known crystal structures [11]. 

Whether a particular metal is known to crystallize in only a close-packed or body-centered cubic form, or in both, we are therefore able to calculate, from its vaporization enthalpy, the bond enthalpy term (M-M) for bonds of a known length d, and so, using the equation (M-M) = Ad -, we can calculate the value of A for that metal. Values of length-energy correlation constants, A, calculated thus are listed in Table 1, with other relevant data. From these we can, in turn, calculate the enthalpies of all of the metal-metal bonds in (homonuclear) cluster compounds of these metals, if their structures, and so their bond lengths, have been determined. 

Bader, Henneker, and Cade have taken the electron probability densities for homonuclear diatomic molecules at as calculated from Hartree-Fock functions and subtracted off the probability densities for the corresponding separated atoms, as calculated from atomic Hartree-Fock wave functions [R. F. W. Bader, W. H. Henneker,... 

The constant electron density contour diagrams of one homonuclear and five heteronuclear diatomic molecules presented in Fig. 8.6 have been obtained by reasonably accurate quantum chemical calculations. The electric dipole moment of F2 is zero by symmetry. The electric dipole moments of heteronuclear molecules like LiFl, LiF, HF, CIF or CO may be calculated from their electron densities using equation (5.2). These dipole moments, in turn, allow us to calculate the ionic characters gic(calc) = /Xei(calc)(calc). In Table 8.1 we compare the calculated ionic characters of 21 heteronuclear diatomic molecules with their experimental counterparts. The agreement between experiment and calculations is good the average deviation between experimental and calculated values is less than 0.02 a.u, the maximum deviation (in KLi) is 0.05 a.u. 

General conditions initiator 20 mmol, toluene 2 ml, [rac-LA]y[Al] 100, temperature 80 C, time 24 hrs. Calculated of PLA (g/mol)= 144.14 x Conversion (LA). Experimental values determined by GPC analysis in THE Determined from the methane region of the homonuclear decoupled H NMR spectrum. Calculated from BemouUian statistics. 20 mmol of PrOH was added to the initiator. 

Besides the highly heteronuclear or heavy homonuclear diatomic molecules investigated so far, we thought it is appropriate to investigate staggering patterns in quasi-homonuclear light molecules. The AJ = 1 staggering patterns for (U2, LO) and (Ul, LO), calculated from the very accurate FT-IR emission... 

The dissociation energies of the homonuclear diatomic molecules, D (R2), were calculated from the mass spectrometrically measured ion currents and the thermal functions evaluated for the gaseous species. The error limits shown in table 1 are upper limits and include those due to experimental uncertainties and also those due to the uncertainties in calculated thermal functions. The Do(R2) values (last column, table 1) also show the double periodicity exhibited by the sublimation enthalpies. This double periodicity comes about because (1) in the thermodynamic calculations the of th rare-earth metals is needed,... 

The simplest model of a covalent bond is based on an electrostatic point-charge simulation of overlapping spherical valence-electron charge clouds that surround monopositive atomic cores. For a homonuclear pair of atoms with radius r and internuclear distance d, the dissociation energy D is calculated from... 

This phenomenon of antiparamagnetic paramagnetic terms clearly needs a name and is called here the Cornwell effect (ideally the Cornwell-Santry effect). Positive contributions to op (which may or may not be positive overall) are expected in heteronuclear diatomics if they have a IT state this excludes, e.g., HF, InF, and TIF. In homonuclear diatomics, the IT -> a excitation is symmetry-forbidden. The possibility has been mentioned for XeF (34), although, from the chemical shift and calculated values of aa, the resultant Op ( F) is negative in XeFg and KrFj (cf. Fig. 7). Another candidate is FC DH, from the evidence of the fluorine chemical shift and spin-rotation interaction (96). According to this interpretation there should be a substantial upheld shift of the... 

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