Ring approximation

In azole chemistry the total effect of the several heteroatoms in one ring approximates the superposition of their separate effects. It is found that pyrazole, imidazole and isoxazole undergo nitration and sulfonation about as readily as nitrobenzene thiazole and isothiazole react less readily ica. equal to m-dinitrobenzene), and oxadiazoles, thiadiazoles, triazoles, etc. with great difficulty. In each case, halogenation is easier than the corresponding nitration or sulfonation. Strong electron-donor substituents help the reaction. 

Dr = diameter of the ring (approximately equal to the shell outside diameter). 

At a pressure of 1 x 10 5 Torr 1,4-cyclohexadiene, the surface shows ordered domains of hexagonal rings approximately 18 A in diameter made up of six adsorbed molecules with an intermolecular distance of approximately 10 A (Figure 7.22a). A ( 43 x y/43)i 7.6° structure was proposed as schematically shown in Figure 7.22b. 1,4-Cyclohexadiene adsorbs in a boat configuration on bridge or hollow sites on the Pt (1 1 1) surface with comparable adsorption energies of 145.6 and 141.6kj mol-1, respectively [39]. 

Compound Number of Rings Approximate Molecular Weight Melting Point (iC) Solubility in Water (mg/L) Log K ... 

In high energy accelerators, electrons are injected into an electron storage ring (approximately 30 m in diameter) captured, and accelerated around this circular path by a... 

The width of the rings approximates the amount of each component.]... 

Moszynski R, Jeziorski B, Szalewicz K (1993) Moller-Plesset expansion of the dispersion energy in the ring approximation. Int J Quantum Chem 45 409-431... 

Relativistic correlation contributions in the LDA have so far only been considered on the basis of a partial resummation of those terms in the perturbation expansion in which are the most relevant in the high density limit. This contribution is either called the ring approximation (in accordance with its diagrammatic form) or, most often, the random phase approximation (RPA - which we shall use here) to ef The detailed discussion of is... 

Likewise, l-bromopentacyclo[4.3.0.0 . 0 .0 ]nonan-9-one ethylene acetal (7) reacted with lithium metal in a mixture of tcrt-butyl alcohol and tetrahydrofuran to give pentacyclo[4.3.0.0. 0 .0 ]nonan-9-one ethylene ketal (8) in 94% yield with no cleavage of the cyclopropane ring. ° Approximately 50% ring opening occurred when e.x o-3-bromo-ex o-5-fluorotricyclo[2.2.1.0 ]heptane was exposed to tributyltin hydride and gave ex o-3-fluoro-tricyclo[2.2.1.0 ]heptane and c t/o-7-fluoronorbornene in nearly 1 1 ratio. ... 

Tilmicosin. The macrolide antibiotic tylosin is a fermentation product of Streptomyces fradiae. Tylosin is converted to desmycosin by acid hydrolysis to remove the mycarose ring and tilmicosin is produced from desmycosin by reductive amination of e C-20 aldehyde with 3,5-dimethylpiperidine (/). Tilmicosin is a mixture of diastereomers having the methyl groups of the piperidine ring approximately 85% cis and 15% trans. 

F2i2i2x Z = 4 Dx = 1.608 R = 0.035 for 643 intensities. The pyranose ring, approximately is distorted by the anhydro bridge, °, which forms a boat-shaped, seven-membered ring. There is no intramolecular hydrogen-bond, and the repulsion of the syn-axial hydroxyl groups also distorts the pyranose ring. 

Two horizontal brass rings (approximately 19.8 mm internal diameters) filled with bituminous binder are placed in a ring holder and heated at a controlled rate in a liquid bath while each supports a steel ball. The softening point is the mean of the temperatures at which the two discs soften enough to allow each ball, enveloped in bituminous binder, to fall a distance of 25.0 mm. 

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