Kaupp studies

Vaara, J., Malkina, O.L., Stoll, H., Malkin, V.G. and Kaupp, M. (2001) Study of relativistic effects on nuclear shieldings using density-functional theory and spin-orbit pseudopotentials. Journal of Chemical Physics, 114, 61-71. 

Kaupp G, Schmeyers J, Naimi-Jamal MR (2001) A practical students course environmentally henign chemical syntheses. Case study for distribution by OECD. Also available athttp //kaupp.chemie.unioldenburg.de... 

That the cycloaddition occurs via the less highly polar exciplex is also supported by Kaupp s studies of photocycloaddition between trans-stilbene and cyclic unsaturated ethers (57). 

Kaupp and McLachlan (2000) has investigated the distribution of PAHs within the full size range of atmospheric particles. The study... 

Two classic studies on polymorphic systems are worthy of note here. One is the difference in the reactivity of the and y-polymorphic forms of meta substimted cinnamic acids 6-XL, in which the instantaneous rates and product distributions varied with time (Hadjoudis et al. 1972). A second example involves the compound 6-XLin (Voght et al. 1963) that has been shown to exist in a number of different crystalline modifications. A chloroform solvate (Schaeffer and Marsh 1969) is reactive towards oxygen, while Bruckner et a/. (1971) have reported the structure of an inactive form. The ability to probe the details of the reactions at the gas-solid interface with atomic force microscopy (Kaupp et al. 1996) and in the bulk by NMR imaging (Butler et al. 1992) has led to increased understanding and renewed interest in these systems that have considerable industrial promise especially due to the avoidance of solvents that otherwise would require disposal or recycling (Dittmer 1997). 

Kaupp and Teufel. The adducts (88), (90), and (89) are formed in respective yields of 81%, 14%, and < 5% from the singlet exci-plex whereas triplet quenching and sensitization studies show that (90) is the major product from the triplet pathway which also yields an adduct of unknown structure. 

Although DFT methods for calculating NMR chemical shifts are still rather young, some standards have already been established. This became possible because systematic studies of the accuracy of the methods in the field have been made by Biihl (91,93), by Kaupp (92,94), by Oldfield and coworkers (95), and by Schreckenbach, Ziegler, et al. (90,96). The most important conclusions of some representative papers shall shortly be summarized. We want to point out, however, that the calculation of NMR parameters for TM compounds is not a trivial task and that it is wise to consult an expert prior to running calculations. Also, much progress can be expected in the next couple of years, which may soon outdate the present recommendations. Yet, it is helpful to see what accuracy can already be expected from present standard methods. 

The so-called heavy-atom chemical shift of light nuclei in nuclear magnetic resonance (NMR) had been identified as a spin-orbit effect early on by Nomura etal. (1969). The theory had been formulated by Pyykktt (1983) and Pyper (1983), and was previously treated in the framework of semi-empirical MO studies (PyykktJ et al. 1987). The basis for the interpretation of these spin-orbit effects in analogy to the Fermi contact mechanism of spin-spin coupling has been discussed by Kaupp et al. (1998b). 

SCFs as solvents for this reaction, for example, Paulaitis and Alexander (1987), Kim and Johnston (1987), Ikushima et al. (1990, 1991, 1992), Isaacs and Keating (1992), Kaupp (1994). The results of these and other studies confirm the expectation that there is no discontinuity in the reaction rate in the transition from fluid to sc CO2 at constant density, but at the same time there is no significant rise in the reaction rate either. An example of a reaction that shows a reasonable increase in the rate constant is the cycloaddition of p-benzoquinone and cyclopentadiene in sc CO2 (Isaacs and Keating, 1992). The rate constant increases with pressure and is about 20% higher than in diethyl ether. 

Several studies report synthesis of nitrogen-containing products in ball mill in which the initial reaction step is formation of an imine bond, followed by addition across the C=N bond in the successive reaction step. Olelinic amines and heterocycles such as thiazolidine and benzimidazole were prepared in this way. Kaupp et al. have carried out several mechanochemical reactions by milling of stoichiometric quantities of (l)-cysteine 311 and paraformaldehyde (in Retsch MM20(X) mill, with a lOmL stainless steel beaker and balls) affording a quantitative yield of the (R)-thiazolidine 312 within 1 h (Scheme 3.86) [31], The crystal water was then removed by drying. The formation of product takes place via an initial imine formation and subsequent cyclization. 

PUme J, Robinson EA, Gillespie RJ (2006) A topological study of the geometry of AFgE molecules Weak and inactive lone pairs. Inorg Chem 45 6198-6204 Kaupp M (2001) Non-VSEPR structures and bonding in d° systems. Angew Chem Int Ed 40 3535-3565... 

Wang XF, Andrew L, Riedel S, Kaupp M (2007) Mercury is a transition metal The first experimental evidence for HgF4. Angew Chem Int Ed 46 8371-8375 Li X, Wang L-S, Boldyrev Al, Simons J (1999) Tetracoordinated planar carbon in the Al4C anion. A combined photoelectron spectroscopy and ab initio study. J Am Chem Soc 121 6033-6038... 

Kacprzak, S., 8c Kaupp, M. (2004). Electronic g-tensors of semiquinones in photosynthetic reaction centers. A density functional study. The Journal of Physical Chemistry B, 108, 2464. 

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