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61.
Thyagarajan S Shay DT Incarvito CD Rheingold AL Theopold KH 《Journal of the American Chemical Society》2003,125(15):4440-4441
Reaction of TpR,MeCo(I) dinitrogen complexes (R = iPr, tBu) with trimethylsilyl azide yields structurally characterized compounds that imply the formation of reactive intermediates of the type TpR,MeCo=NSiMe3. These cobalt imido species apparently abstract hydrogen from the 3-substituent of the Tp-ligand, leading to the formation of amido complexes accompanied by either Co-C bond formation (R = tBu) or C-C bond formation (R = iPr). 相似文献
62.
Klaus B. Wenzel 《Journal of computational chemistry》1982,3(2):191-207
It is shown that even the CPMET approximation for the contributions of fourfold excitations can be replaced by a more sophisticated method. Furthermore, an approximation is presented for the contributions of threefold excitations which are neglected in CPMET . Finally, it is described how the advantages of different CEPA methods can be united in a single CEPA scheme (called CEPA -U). The various approximations are discussed in terms of Slater determinants, and it is shown how the relatively large amount of details can be handled with the help of computer programs, i.e., how knowledge engineering can be successfully applied here. 相似文献
63.
Azomethine ylide 3 , generated by thermolysis of 3,4-diphenyl-Δ1-1,2,3-triazoline-5,5-dimethyldicarboxylate 1 , can be trapped by isonitriles to give 3-imino-1,4-diphenylazetidine-2,2-dimethyldicarboxylates 5 . The IR, 1H-NMR, 13C-NMR and mass spectral data of the new compounds are discussed. 相似文献
64.
Hans-Dietrich Stachel K. Klaus Harigel Hermann Poschenrieder Hans Burghard 《Journal of heterocyclic chemistry》1980,17(6):1195-1199
Alkyl cyanoacetate, malonate, acetoacetate and methylsulfonyl acetic acid ethyl ester are acylated by alkylidenazlactones. The acyl compounds easily form alkylideneteramic acids by condensations. The acylcyanoacetates 2 isomerize into aminopyrrolinones 3 via acid catalysis. 相似文献
65.
Klaus Burger Elisabeth Windeisen Elisabeth Heistracher Torsten Lange Abdel-Aleem H. Abdel-Aleem 《Monatshefte für Chemie / Chemical Monthly》2002,2(3):41-58
The synthesis of homochiral heterocyclic α-hydroxy acids starting from (S)- and (R)-malic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building
blocks for peptide and depsipeptide modification. 相似文献
66.
Photo-extrusion of nitrogen from the azoalkane 1 in the presence of molecular oxygen gave besides the hydrocarbons 3 and 5, the endoperoxide 10 and hydroperoxide 11, the former via trapping of the 1,4-diradical 4 by triplet oxygen, the latter by ene-reaction-6f hydrocarbon 5 with singlet oxygen. 相似文献
67.
Klaus Helfrich 《Theoretical chemistry accounts》1971,21(4):381-397
If χ i (χ k ) is an exact generalized diatomic orbital (solution of Eq. (1) of text), a sequence of functions χ i (N) converging to χ i may be constructed so that matrix elements of frequently occurring operators between χ i (N) and χ k (N) may be computed without any numerical integration. Exact expectation values are given for kinetic and potential energy, dipole moment, θ 2=x 2+y 2, and quadrupole moment 3z 2?r 2, for various ratios of nuclear charges Z 1,Z 2 and for several distances R. Special subjects discussed in terms of computed expectation values are:
- R-dependence of the contributions to total energy of HeH2+ in state 2pσ and of LiH3+ in state 3dσ
- RZ-and λ-dependence of dipole and quadrupole moment functions in state 1sσ
- Some properties of those generalized diatomic orbitals which approach, for R going to 0, Slater-type atomic functions.
68.
Two methods are proposed, one for the location of saddle points and one for the calculation of steepest-descent paths on multidimensional surfaces. Both methods are based on a constrained simplex optimization technique that avoids the evaluation of gradients or second derivative matrices. Three chemical reactions of increasing structural complexity are studied within the PRDDO SCF approximation. Predicted properties of reaction hypersurfaces are in good overall agreement with those determined by gradient minimization and gradient following algorithms in connection with various ab initio SCF methods. Computational efforts required by the new procedures are discussed. 相似文献
69.
Boström J Böhm M Gundertofte K Klebe G 《Journal of chemical information and computer sciences》2003,43(3):1020-1027
The molecular alignments obtained from a previously reported pharmacophore model have been employed in a three-dimensional quantitative structure-activity relationship (3D QSAR) study, to obtain a more detailed insight into the structure-activity relationships for D(2) and D(4) receptor antagonists. The frequently applied CoMFA method and the related CoMSIA method were used. Statistically significant models have been derived with these two methods, based on a set of 32 structurally diverse D(2) and D(4) receptor antagonists. The CoMSIA and the CoMFA methods produced equally good models expressed in terms of q(2) values. The predictive power of the derived models were demonstrated to be high. Graphical interpretation of the results, provided by the CoMSIA method, brings to light important structural features of the compounds related to either low- or high-affinity D(2) or D(4) antagonism. The results of the 3D QSAR studies indicate that bulky N-substituents decrease D(2) binding, whereas D(4) binding is enhanced. Electrostatically favorable and unfavorable regions exclusive to D(2) receptor binding were identified. Likewise, certain hydrogen-bond acceptors can be used to lower D(2) affinity. These observations may be exploited for the design of novel dopamine D(4) selective antagonists. 相似文献
70.