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451.
The oscillator model is used to compute the Heitler-London energy and the exchange potential for two interacting hydrogen atoms. With a single oscillator frequency it is not possible to obtain satisfactory results. Allowing the oscillator frequency to vary with internuclear separation enables reasonable values to be obtained. 相似文献
452.
Michael J. Bearpark Nicholas C. Handy Roger D. Amos Paul E. Maslen 《Theoretical chemistry accounts》1991,79(5):361-372
Summary The MP2-R12 method was introduced by Kutzelnigg and Klopper to overcome the problem caused by truncation of the one electron basis set in correlation energy calculations at the Møller-Plesset second order level of approximation. Here, we have evaluated the integrals required by their simplest scheme using the Rys-quadrature procedure. Results are presented for Ne, H2O, and HF using largespdf gaussian basis sets. 相似文献
453.
The total synthesis of (-)-kendomycin (1), a novel macrocyclic polyketide with antibacterial and antitumor activity, was achieved in 21 steps (longest linear sequence) exploiting an effective Petasis-Ferrier union/rearrangement tactic to construct the tetrahydropyran ring, a ring-closing metathesis to generate the macrocycle, and a biomimetic quinone-methide-lactol assembly. 相似文献
454.
A. T. Amos 《Theoretical chemistry accounts》1967,7(1):20-24
The first order changes in the orbital energies of a number of hydrocarbons due to perturbations at particular atoms are given. These are useful for discussing ionization potentials, polarographic reduction and oxidation potentials, and electron affinities of heteromolecules.
Zusammenfassung Die Änderungen erster Ordnung von Einelektronenenergien bei Störung an bestimmten Atomen werden für eine Reihe von Kohlenwasserstoffen angegeben. Sie erweisen sich als brauchbar für die Diskussion von Ionisationspotentialen, polarographischen Oxydations- und Reduktionspotentialen und Elektronenaffinitäten von Heteromolekülen.
Résumé Les variations au premier ordre des énergies des orbitales, sous l'influence de perturbations sur des atomes déterminés, sont données pour un certain numbre d'hydrocarbures. Elles sont utiles pour la discussion des potentiels d'ionisation, des potentiels d'oxydation et de réduction polarographiques et des affinités électroniques des molécules hétéroatomiques.相似文献
455.
Smith AB Kanoh N Ishiyama H Minakawa N Rainier JD Hartz RA Cho YS Cui H Moser WH 《Journal of the American Chemical Society》2003,125(27):8228-8237
A convergent, stereocontrolled total synthesis of the architecturally complex tremorgenic indole alkaloid (-)-penitrem D (4) has been achieved. Highlights of the synthesis include an efficient, asymmetric synthesis of the western hemisphere; the stereocontrolled assembly of the I-ring; discovery of a novel autoxidation to introduce the C(22) tertiary hydroxyl group, required for tremorgenic activity; union of fully elaborated eastern and western hemispheres, exploiting an indole synthetic protocol developed expressly for this purpose; and a late-stage, stereoselective construction of the A and F rings exploiting a Sc(OTf)(3-)promoted reaction cascade. The longest linear sequence leading to (-)-penitrem D (4) was 43 steps. 相似文献
456.
Symmetry-adapted double perturbation theory is applied to the Frost model. Even when used only through zero-order in the correcting ”internal“ perturbation it gives values of average electric polarizabilities in fair agreement with experiment. If the model is extended by employing clliptical gaussians rather than spherical ones, the anisotropy of the molecular polarizability can be determined. 相似文献
457.
Shaw SJ Sundermann KF Burlingame MA Myles DC Freeze BS Xian M Brouard I Smith AB 《Journal of the American Chemical Society》2005,127(18):6532-6533
A series of simplified discodermolide analogues have been designed and synthesized in an attempt to understand the role of the lactone ring. These synthetic efforts have led to an unsubstituted butyrolactone 9 being generated, which shows improved activity over the natural product. 相似文献
458.
Barfod R Eriksen J Golding BT Hammershøi A Jacobsen TA Langkilde A Larsen S Mønsted O Sargeson AM Sørensen HO 《Dalton transactions (Cambridge, England : 2003)》2005,(3):491-500
New hexadentate polyamine monocarboxylate ligands, 11-amino-9-(2-aminoethyl)-3,6,9-triazaundecanoate (tren-engly-), 12-amino-10-(2-aminoethyl)-3,7,10-triazadodecanoate (tren-tngly-) and 13-amino-11-(2-aminoethyl)-3,8,11-triazatridecanoate (tren-bngly-), were synthesized by intramolecular coupling of tetradentate tris(2-aminoethyl)amine (tren) and didentate N-([small omega]-formylalkyl)glycinates, OCH(CH2)nNHCH2CO2-, in easily and stereoselectively assembled cobalt(III) templates, p-[Co(tren){(RO)2CH(CH2)nNHCH2CO2}](O3SCF3)2, n = 1-3 (R = Me or Et). The reaction sequences comprised assembly of the template from [Co(tren)(O3SCF3)2]O3SCF3 (1) and (RO)2CH(CH2)nNHCH2CO2Et, deprotection of the pendant acetal in acid, intramolecular condensation of the resulting aldehyde with a coordinated primary amine at intermediate pH to form the imine and reduction of this by NaBH4. For n= 1, imine formation occurred exclusively at the primary amine trans to the carboxylate producing the hexadentate 11-amino-9-(2-aminoethyl)-3,6,9-triazaundeca-5-enoato (tren-enimgly-) complex, i-[Co(tren-enimgly)]Cl2.3.5H2O. In all instances, subsequent imine reduction gave the s isomer complex, exclusively. Complexes p-[Co(tren){(MeO)2CHCH2gly}](O3SCF3)2 (3), i-[Co(tren-enimgly)]ZnCl4.H2O (5), s-[Co(tren-engly)]ZnCl(4)(s-6), s-[Co(tren-tngly)]ZnCl4.H2O (s-7) and s-[Co(tren-bngly)ZnCl3]2ZnCl4 (s-8) were structurally characterized by X-ray crystallography. Charcoal-catalyzed equilibration of s-[Co(tren-engly)]Cl(2).2H(2)O dissolved in water produced the s- (s-6), p- (p-6) and t-[Co(tren-engly)]2+ (t-6) isomers in comparable amounts. p-6 and t-6 were also structurally characterized as their tetrachlorozincate and chloride salts, respectively. In base-catalyzed reactions, s-6 and t-6 each also formed p-6. Reduction of s-[Co(tren-engly)]Cl2.2H2O with (NH4)2S and acidification liberated the pentaamino carboxylic acid ligand which was isolated as the hydrochloride salt. 相似文献
459.
[structure: see text] The design, total synthesis, and biological evaluation of two C13-C14-cyclopropyl analogues [(+)-1 and (+)-2] of (+)-discodermolide have been achieved. Key features of the syntheses include highly stereoselective, hydroxyl-directed cyclopropanations of vinyl iodides and higher order cuprate-mediated cross-coupling reactions between cyclopropyl iodides and alkyl iodides. Biological evaluation revealed that neither orientation of the cyclopropyl methylene completely substitutes for the C14 methyl found in (+)-discodermolide (3). 相似文献
460.
Let be a positive number, and letE
n,n
(x
;[0,1]) denote the error of best uniform rational approximation from
n,n
tox
on the interval [0,1]. We rigorously determined the numbers {E
n,n
(x
;[0,1])}
n
=1/30
for six values of in the interval (0, 1), where these numbers were calculated with a precision of at least 200 significant digits. For each of these six values of , Richardson's extrapolation was applied to the products
to obtain estimates of
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