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171.
Dr. W. Gottardi 《Monatshefte für Chemie / Chemical Monthly》1975,106(3):611-623
By reaction of primary carboxamides with “dibromoisocyanuric acid” (DBI) N-monobromoamides can be readily obtained as well as the N,N-dibromoamides described in an earlier paper1. Reactions, some of them new, and properties of these compounds are described and compared with those of the N,N-dibromoamides. Like other compounds bearing the NHBr group2, 3 the N-monobromocarboxamides disproportionate at room temperature according to: 2 RCONHBr ? ? RCONH2+RCONBr2. For CH3CONHBr the equilibrium constant was found to beK=0.02. In aqueous solution they behave as weak acids. The dissociation constants of eight compounds [R=?CH3, ?C2H5, ?CH2Cl, ?CHCl2, ?CCl3, ?CF3, ?C(CH3)3 and ?C6H5] were measured: they differ from those of the corresponding carboxylic acids by about three powers of ten. 相似文献
172.
J. G. C. M. van Duijneveldt-van de Rijdt Dr. F. B. van Duijneveldt 《Theoretical chemistry accounts》1970,19(1):83-91
Using perturbation theory of intermolecular forces (including exchange effects) hydrogen-bond energies are calculated for a simple model representing the water dimer. Several orientations of the proton acceptor with respect to the O...O axis are considered and it is found that the optimum orientation depends sensitively on the oxygen lone-pair hybridization assumed. The main orientation-dependent energy term is found to be the classical electrostatic energy between the unperturbed molecules. The relation of the present results to the structures of the ices I and Ic, and to the results of recent SCF studies are discussed briefly.
For some recent CNDO/2 calculations on (H2O)2 which concentrate mainly on rotations of the donor see Ref. [5]. 相似文献
Zusammenfassung Die Energien von Wasserstoffbindungen werden für ein einfaches Modell des dimeren Wassers mit Hilfe der Störungstheorie für intermolekulare Kräfte (mit Austauscheffekten) berechnet. Verschiedene Orientierungen des Protonen-Akzeptors bezüglich der O ... O-Achse werden untersucht; man findet, daß die optimale Orientierung empfindlich von der angenommen Hybridisierung des einsamen Elektronenpaars des Sauerstoffs abhängt. Der hauptsächliche, von der Orientierung abhängige Energieterm ist die klassische elektrostatische Energie zwischen den beiden ungestörten Molekülen. Die Beziehung der vorliegenden Ergebnisse zu den Strukturen von Eis I und Ic sowie zu den Ergebnissen kürzlicher SCF-Rechnungen wird kurz diskutiert.
For some recent CNDO/2 calculations on (H2O)2 which concentrate mainly on rotations of the donor see Ref. [5]. 相似文献
173.
Ketoses, as fructose and sorbose, react with ZrOCl2 after slight heating. The reaction mixture exhibits strong fluorescence in UV; increased absorption is shown at 220–230 nm and a characteristic maximum at 335 nm. There is also an increase in conductivity. The stoichiometric composition of the fluorescing ketose-Zirconium chelate compound has been determined by a Job diagram. This compound can be used as a sensitive optical test in the microdetermination of ketoses. 相似文献
174.
Dr. E. M. Evleth 《Theoretical chemistry accounts》1968,11(2):145-155
The electronic structures of pyridinen-oxide, 2- and 4-methoxypyridinen-oxide, their conjugate acids, and 2- and 4-pyridone are calculated using the Pariser-Parr-Pople SCF-CI approximation. The results indicate that the1
B
11
A
1 transition of pyridinen-oxide lies in the same energy region as the transition previously assigned as beingn -*. The strong electronic transitions in the 250–280 m region of pyridine-n-oxide, 4-methoxypyridinen-oxide, and 4-pyridone are assigned as being1
A
11
A
1.
Zusammenfassung Die elektronischen Strukturen von Pyridin-N-Oxyd, 2- und 4-Methoxypyridin-N-Oxyd, ihrer Kationen, und von 2- und 4-Pyridon wurden nach der Methode von Pariser-Parr-Popple SCF-CI berechnet. Es ergibt sich, daß der1 B 11 A 1 Übergang des Pyridin-N-Oxyds etwa die gleiche Energie besitzt, wie die bisher einemn -* Übergang zugeordnete Bande. Der intensitätsstarke Übergang des Pyridin-N-oxyds, 4-Methoxypyridin-N-oxyds und 4-Pyridons im Bereich von 250–280 m wird einem1A11 A 1 Übergang zugeordnet.
Résumé Les structures électroniques de l'oxyde de pyridine, desn-oxydes de 2- et 4-methoxypyridine, leurs cations, et les 2- et 4-pyridone sont calculés par l'approximation Pariser-Parr-Pople SCF-CI. Les résultats obtenus indiquent que la transition1 B 11 A 1 dun-oxyde de pyridine est située dans la même région d'énergie que la transition assignée auparavant comme étantn -*. Les transitions électroniques fortes dans la région de 250–280 m dun-oxyde de pyridine, dun-oxyde de 4-methoxypyridine et du 4-pyridone sont assignées comme étant1 A 11 A 1.相似文献
175.
Dipl.-Ing. Dr. O. Hinterhofer 《Monatshefte für Chemie / Chemical Monthly》1974,105(2):279-290
The selective chlorination of a m/p-xylene mixture, followed by distillation of the unreacted p-xylene, leaves a residue containing up to 90% of monochlorinated m-xylenes. m-Xylene is recovered from the latter by heterogeneous catalytic hydrogenolysis in the gas-phase. It was found that the hydrogenolysis on certain noble metal catalysts proceeds according to an ionic reaction mechanism at temperatures below a definite temperature range. At temperatures above this range hydrogenolysis follows a radical reaction mechanism. 相似文献
176.
Dr. Rud Wegsheider 《Monatshefte für Chemie / Chemical Monthly》1896,17(1):111-120
Zusammenfassung Zu den früher von mir angeführten Gründen, welche für die aufgestellten Formeln der isomeren Opiansäureester sprechen, sind noch in erster Linie das Verhalten gegen Phenylhydrazin, sowie nach Versuchen Liebermann's das Verhalten gegen -Naphtylamin und Semicarbazid, in zweiter Linie das Verhalten gegen fuchsinschwefelige Säure, Diazobenzol-p-Sulfosäure und vielleicht auch das Verhalten gegen Essigsäureanhydrid und Natriumacetat hinzuzufügen. Da somit die Constitution der Opiansäureester genügend feststeht, ist eine Überprüfung der Beobachtungen Stabil's über die Ester der Phtalaldehydsäure wünschenswerth.Die Aldehydreactionen mit Resorcin und mit Nitroprussidnatrium versagen bei der Opiansäure und ihren Estern; auch die anderen oben erwähnten Farbenreactionen sind hier von geringem Werth. 相似文献
177.
Semiempirical calculations, at the PM3 level provided within the Winmopac v2.0 software package, are used to geometrically optimize and determine the absolute energies (heats of formation) of a variety of C(20) isomers that are predicted to exist in and around the ring and cage isomers. Using the optimized Cartesian coordinates for the ring and the cage isomers, a saddle-point calculation was performed. The resulting energy profile, consisting of a series of peaks and valleys, is used as a starting point for the identification and location of fifteen additional isomers of C(20) that are predicted to be energetically stable, both via geometry optimizations and force constant analysis. These additional isomers were subsequently determined to lie adjacent to one another on the potential surface and establish a step-wise transformation between the ring and the cage. Transition-state optimization of the Cartesian coordinates at the saddle point between adjacent isomers was performed to quantify the energy of the transition state. The step-wise process from one isomer to another, which extends out over the three-dimensional surface, is predicted to require approximately 15% less energy than that of the direct, two-dimensional transformation predicted in the bowl-cage profile. However, the net atomic rearrangement for the step-wise process is about four times greater than that of the direct process. Although less in energy, the amount of atomic rearrangement in the step-wise process would make the occurrence of such a route prohibitive. Utilizing the direct distance separating the three primary isomers (ring, bowl, cage), the method of triangulation is performed to quantitatively position other C(20) structures on the potential surface, relative to the ring, bowl, and cage isomers. 相似文献
178.
Schormann M Garratt S Hughes DL Green JC Bochmann M 《Journal of the American Chemical Society》2002,124(38):11266-11267
The reaction of the tin-substituted propene Me3Sn(R)CHCH=CHR (R = SiMe3) with MCl4 in dichloromethane in the presence of Me3SnCl gives the first examples of isolable sec-alkyl carbocation salts, [HC{CH(R)SnMe3}2]+M2Cl9- (M = Zr, Hf). The compounds are thermally stable and, unlike previously isolated trialkyl carbocations, do not require superacidic media or weakly coordinating anions for stability. The crystal structure and DFT calculations suggest polarization of the Sn substituents and hyperconjugation as the reason for the unexpected stability. The stabilizing effect of tin is significantly stronger than that of Si. The carbocations are effective initiators for the polymerization of isobutene, isoprene, and alpha-methylstyrene. 相似文献
179.
Mechanism of Thermal Dehydration of Sodium Dihydrogenphosphate The thermal dehydration of sodium dihydrogenphosphate (P1) to sodium cyclotriphosphate (CP3) and sodium polyphosphate, the so-called Maddrell's salt (MS), is controlled by nucleation and crystallization of CP3 and MS, respectively. The wellknown influence of various formation conditions on the CP3:MS product ratio is caused by amorphous and crystalline intermediate phases and their ability to form CP3 or MS nuclei. On seeding P1 with CP3 or MS the dehydration proceeds structure-controlled via dihydrogendiphosphate to pure CP3 or pure MS. The particularities of thermal dehydration of crystalline sodium dihydrogendiphosphate, and also the dehydration and reorganization of sodium phosphate glasses (Na:P = 1:1) with different mean chain lengths, under formation of CP3 or MS are described. 相似文献
180.
Paul D. Beer Zheng Chen Philip A. Gale Jennifer A. Heath Rachel J. Knubley Mark I. Ogden Michael G. B. Drew 《Journal of inclusion phenomena and macrocyclic chemistry》1994,19(1-4):343-359
The synthesis, metal, ammonium and alkyl ammonium cation coordination chemistry and electrochemical recognition studies of new diester-and diamide-calix[4]arenediquinone receptors are described. In addition the synthesis and coordination properties of a novel diamide benzo-15-crown-5-calix[4]arene molecule is reported.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes. 相似文献