Combined experimental and

Figure B2.5.20. The combined experimental and theoretical approach Molecular spectra and motion (after [18]).

In a combined experimental and theoretical investigation it was found that the / -alkyl group in the dienophile gave a steric interaction in the transition-state structure which supported the asynchronous transition-state structure for the Lewis acid-catalyzed carbo- and hetero-Diels-Alder reactions. The calculated transition-state energies were of similar magnitude as obtained in other studies of these BF3-catalyzed carbo-Diels-Alder reactions. 

Thus, the combined experimental and theoretical results indicate that the chemical shift observed for the S(2p) core level, of about 1.6 eV, should be due to a secondary effect from the attachment of Al atoms to the adjacent carbon atoms. Indeed, this is fully consistent with tib initio Hartree-Fock ASCF calculations of the chemical shifts in aluminum-oligolhiophene complexes 187], From calculations on a AI2/a-3T complex, where the two AI atoms are attached to the a-car-bons on the central thiophene unit, the chemical shift of the S(2p) level for the central sulfur atom is found to be 1.65 eV, which is in close agreement with the experimental value of about 1.6 eV [84]. It should be pointed out that although several different Al-lhiophene complexes were tested in the ASCF calculations, no stable structure, where an Al atom binds directly to a S atom, was found [87]. 

At a close level of scrutiny, real systems behave differently than predicted by the axial dispersion model but the model is useful for many purposes. Values for Pe can be determined experimentally using transient experiments with nonreac-tive tracers. See Chapter 15. A correlation for D that combines experimental and theoretical results is shown in Figure 9.6. The dimensionless number, udt/D, depends on the Reynolds number and on molecular diffusivity as measured by the Schmidt number, Sc = but the dependence on Sc is weak for... 

In a recent study, combining experimental and theoretical investigation. Suits and co-workers [8] discovered two active pathways in the photodissociation... 

The combined experimental and theoretical investigation of Dixon et al. [75] applied the H-atom Rydberg time-of-flight method to measure the translational energy distribution of H atoms from the photodissociation... 

Cao D, Lu G-Q, Wieckowski A, Wasileski SA, Neurock M. 2005. Mechanisms of methanol decomposition on platinum A combined experimental and an initio approach. J Phys ChemB 109 11622-11633. 

The issue of regioselectivity in oxidations of a-tocopherol-type antioxidants— being an open question for more than 70 years—was recently clarified by a combined experimental and theoretical study.38 The approach was based on measuring the ratio between the down-o-QM and up-o-QM products obtained upon oxidation of 10 different a-tocopherol-type antioxidants (1, 15a-i), which carried differently sized alicycles (Fig. 6.13). Thus, in these compounds the electronic effects were kept... 

Gustavsson T, Banyasz A, Lazzarotto E, Markovitsi D, Scalmani G, Frisch MJ, Barone V, Improta R (2006) Singlet excited-state behavior of uracil and thymine in aqueous solution a combined experimental and computational study of 11 uracil derivatives. J Am Chem Soc 128 607-619... 

Values are estimated from references [152] and [153], which combine experimental and computational values for the reaction free energies and activation energies of relevant reactions in solution. 

The use of organic polymers as conductors and semiconductors in the electronics industry has led to a huge research effort in poly(thiophenes), with a focus on the modification of their electronic properties so that they can behave as both hole and electron conductors. Casado and co-workers [60] have performed combined experimental and theoretical research using Raman spectroscopy on a variety of fluorinated molecules based on oligomers of thiophene, an example of one is shown in Figure 7. 

Depke, G., N. Heinrich, and H. Schwarz. 1984. On the Gas Phase Chemistry of Ionize Glycine and Its Enol. A Combined Experimental and Ab Initio Molecular Orbital Study. Int. J. Mass Spectrom. Ion Porcesses 62, 99-117. 

In this study, the distribution of Al atoms over the individual T sites of the ZSM-5 framework is examined by a combined experimental and computational approach. Eleven differently prepared samples of ZSM-5 were studied by 27Al 3Q MAS NMR spectroscopy. To interpret the observed NMR spectra, we calculated the isotropic shift of Al occupying all the distinguishable T sites of ZSM-5 and used the calculated isotropic shifts to assign the observed resonances to individual distinguishable T sites. 

Allmaras et al. (2004) developed a C-budgeting approach based on combining experimental and isotopic techniques. The data needed to use calculations derived by Allmaras et al. (2004) required that the experiment contain com stover harvested and removed treatments. These calculations assume that the removal of above-ground biomass will not influence the sequestering of below-ground biomass. The SOC derived from com stover (sSOC) is calculated with the equation ... 

Table 3 collects the results obtained by different authors on the reaction of 0s04(NH3) with ethylene. Though the methods were not identical, the results are very similar, and in all cases there is a clear preference of the [3+2] over the [2+2] pathway. Additional confirmation was provided by a combined experimental and theoretical study using kinetic isotope effects (KIEs) to compare experiment and theory. Kinetic isotope effects were measured by a new NMR technique [25] and compared to values, which are available from calculated transition states. It showed that indeed only the [3+2] pathway is feasible [10]. 

The thio-Wittig reaction, like the Wittig itself, may involve (thia)phosphetane or betaine-type structures as intermediates. A combined experimental and theoretical study over a wide range of conditions and of substrates (aliphatic vs aromatic, aldehyde- vs ketone-derived) suggests a mechanistic continuity, with solvent polarity and substrate electronic effects being the main influences on the transition from one mechanism to another. ... 

De Souza R, da Penha ET, Milagre HMS, Garden SJ, Esteves PM, Eberlin MN, Antunes OAC (2009) The three-component Biginelli reaction a combined experimental and theoretical mechanistic investigation. Chem Eur J 15 9799-9804... 

In computational science and engineering, researchers frequently speak of multiple time-scale problems. These are problems ivhere the characteristic times for events span many orders of magnitude. More often than not, the full range of desired time-scales is not experimentally accessible. The combined experimental and numerical approach must settle for analysis of a narrow ivindoiv of time-scales. For most of our purposes, the half-life of an event w ill prove to be a useful definition of characteristic time-scale... 

R. Kapre, K. Ray, I. Sylvestre, T. Weyhermiiller, S. DeBeer George, F. Neese, and K. Wieghardt, Molecular and electronic structures of oxo-bis(benzene-l,2-dithiolato)chromate(V) monoanions. A combined experimental and density functional study, Inorg. Chem., 45 (2006) 3499-3509. 

The development of mixture sorption kinetics becomes increasingly Important since a number of purification and separation processes involves sorption at the condition of thermodynamic non-equilibrium. For their optimization, the kinetics of multicomponent sorption are to be modelled and the rate parameters have to be identified. Especially, in microporous sorbents, due to the high density of the sorption phase and, therefore, the mutual Influences of sorbing species, a knowledge of the matrix of diffusion coefficients is needed [6]. The complexity of the phenomena demands combined experimental and theoretical research. Actual directions of the development in this field are as follows ... 

In marked contrast to the generally accepted mechanism, the involvement of a radical pair produced by an alkene-induced 0—0 bond homolysis was suggested by Minisci and coworkers . In a combined experimental and theoretical study Curci, Houk and coworkers sought to differentiate between a radical pathway and the commonly accepted concerted mechanism. Both product and kinetic smdies tended to exclude a radical pathway. Computational studies at the B3LYP/6-31G level on the epoxidation of isobutylene with DMDO predicted an activation energy = 15.3 kcalmor ) significantly lower... 

The most convincing evidence for an essentially synchronous peracid epoxidation of simple alkenes came from a combined experimental and theoretical study by Singleton, Honk and coworkers. Experimental KIEs for the reaction of m-CPBA with 1-pentene, determined by the clever methodology developed by Singleton and Thomas utilizing the combinatorial high-precision determination of C and H KIEs at natural abundance, confirmed the symmetrical or nearly symmetrical nature of this epoxidation TS. These data were corroborated by B3LYP/6-31G calculations on propylene that supported a synchronous transition state for peroxyformic acid epoxidation. 

With a combined experimental and theoretical study, the observed Swanson humps on W(IOO), W(llO), and Mo(lOO) were soon identified as due to surface states (see Plummer and Gadzuk, 1970). 

Gold clusters adopt planar structures with larger numbers of atoms than silver and copper clusters, as demonstrated by combined experimental and theoretical studies . 

For a combined experimental and computational approach to carbon atom chemistry see C. M. Geise, C. M. Hadad, F. Zheng, and P. B. Shevlin, An Experimental and Computational Evaluation of the Energetics of the Isomeric Methoxyphenylcarbenes Generated in Carbon Atom Reactions, J. Amer. Chem. Soc. 2002, 124, 355. 

The MgO+ ion has significant radical character and reacts via electron transfer (equation 32). It is also a potent H atom acceptor, readily reacting with water via H atom abstraction (equation 33, X = HO). A recent combined experimental and theoretical study reveals that the MgO+ ion readily activates the C—H bond of methane to yield MgOH+ as the major product ion (equation 33, X = CH3) as well as Mg+ as a minor product ion via O atom insertion into the C—H bond (equation 34). ... 

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