In theoretical work, the molecular complex was built (Scheme 5) with the methane guest molecule in close proximity to one of the thiono-sulfurs of the model compound and the P1=S-H-C unit was aligned in the plane of the S=P1-S bonds. The distance, d, between the sulfur and the carbon in the P1=S-H-C fragment was varied in the range 2.4-4.1 A. Several DFT GIAO calculations [Pg.104]

An analysis of the solvent dependence of the A>c and /hh couplings combined with an analysis of the changes in the IR first overtone carbonyl bond intensities and theoretical calculations allowed Abraham and co-workers to determine directly the conformational equilibria in 2-bromocyclo-hexanone, a model compound, by the use of which the authors illustrated an improved method of conformational analysis of substituted cyclohexanones. [Pg.148]

Information about the catalytic cycle and catalytic intermediates is obtained by four methods kinetic studies, spectroscopic investigations, studies on model compounds, and theoretical calculations. Kinetic studies and the macroscopic rate law provide information about the transition state of the rate-determining step. Apart from the rate law, kinetic studies often include effects of isotope substitution and variation of the ligand structure on the rate constants. [Pg.28]

To fulfill the need for understanding what structures will allow enhancement of optical nonlinearity, we have coupled ab-initio theoretical calculations of optical nonlinearity with synthesis of sequentially built and systematically derivatized model compounds, and the measurement of their optical nonlinearities. Now I would like to discuss very briefly our efforts to compare microscopic optical nonlinearities. An expression, similar to the expansion of the bulk polarization as a function of the applied field, can be written for the induced dipole moment. Naturally, the nonlinear term Y, for example, is the third derivative of the induced dipole moment with respect to the applied field. Also, using the Stark energy analysis, one can write the nonlinear terms 3 (and Y) as a sum over all excited states terms involving transition-dipoles and permanent dipoles, similar to what one does for polarizability. Consequently, the two theoretical approaches are (i) the derivative method and (ii) the sum-over-s1j tes method. We have used the derivative method at the ab-initio level. We correlate the predictions of these calculations with measurements on systematically derivatized and sequentially built model compounds. Some conclusions of our theoretical computations are as follows [Pg.570]

We have used 2,7-disubstituted naphthyridines with hydroxy and amido groups to achieve a variety of molecular structures including M and P helices. A combination of X-ray crystallography and theoretical calculations on model compounds (B3LYP/6-31+G ) was used to discuss the tautomerism and the hydrogen bonds of compounds 106-111 [114], Compound 111 was used in the calculations instead of 108. [Pg.171]

X-ray analysis of 2-phenylmethylamino-5-phenyl-A-2-thiazoline-4-one (176), which exists in the keto form in the solid state (420), and of 4,4 -diacetoxy-5,5 -dimethy]-2,2 bithiazolyl (177) (419) are available as model compounds for theoretical calculations (Scheme 92). [Pg.218]

As mentioned, we also carried out IR studies (a fast vibrational spectroscopy) early in our work on carbocations. In our studies of the norbornyl cation we obtained Raman spectra as well, although at the time it was not possible to theoretically calculate the spectra. Comparison with model compounds (the 2-norbornyl system and nortri-cyclane, respectively) indicated the symmetrical, bridged nature of the ion. In recent years, Sunko and Schleyer were able, using the since-developed Fourier transform-infrared (FT-IR) method, to obtain the spectrum of the norbornyl cation and to compare it with the theoretically calculated one. Again, it was rewarding that their data were in excellent accord with our earlier work. [Pg.143]

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