Unexpected Result of Thiophosphorylation of 6-Aminopyrano[2,3-c]pyrazole-5-carbonitrile Derivative

Russian Journal of General Chemistry - The reaction of 6-amino-3-methyl-4-(2,4-dichlorophenyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile with phosphorus sulfide in boiling pyridine...     

Estimation of time characteristics of millimeter-band signals on sea path at small grazing angles

Result are presented for an experimental study of fluctuations of signal arrival angle and intensity and the crosscorrelation of fluctuations of signal amplitude and phase difference at a wavelength of 8.3 mm at spatially separated antennas for two versions of a 14.5-km sea path.Sevastopol Instrument-Engineering Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 6/7, pp. 483–487, June–July, 1992.     

Spectral luminescent properties of 5-(2-hydroxyphenyl)-3-ethyl-1-(pyridin-2-yl)-1Н-1,2,4-triazole and its Be(II) complex

Russian Journal of General Chemistry - The interaction of 4-oxo-1,3-benzoxazinium perchlorate with 2-pyridylhydrazine has given 5-(2-hydroxyphenyl)-3-ethyl-1-(pyridin-2-yl)-1Н-1,2,4-triazole...     

Mechanisms of circumambulatory rearrangements of 5-halogeno-1,2,3,4,5-pentamethoxycarbonylcyclopentadienes

Possible paths of halogen atom migration in 5-halogeno-1,2,3,4,5-pentamethoxycarbonylcyclopentadienes were studied using the density functional theory. The calculations revealed preferential 1,5(in comparison with 1,3-) sigmatropic shifts of halogen atoms along the perimeter of the five-membered ring with the energy barriers ΔE _ZPE ^≠ = 42.9, 26.9, 19.8, and 15.4 kcal mol^–1 for the fluoro-, chloro-, bromo-, and iodosubstituted derivatives, respectively. The calculated charges of halogen atoms in the structures of transition states for 1,5-shifts change from negative for the fluorine atom to positive for the iodine atom (–0.356 (F), 0.019 (Cl), 0.052 (Br), 0.184 e (I)). The migration capacity increases in the order F < Cl < Br < I with an increase in the atomic radius of halogen.     

Structure and fluxional behavior of pentamethoxycarbonylcyclopentadiene

Quantum-chemical calculations by the density functional theory method at the B3LYP/6- 311++G** level have shown that the fulvene form of pentamethoxycarbonylcyclopentadiene 1 in the gas phase is more favorable in energy than cyclopentadiene form 2 by ΔE_ZPE = 7.8 kcal/mol. The fluxional behavior of fulvene 1, detected by dynamic NMR can be explained by the mechanism of circular low-barrier 1,9-O,O'-H shifts accompanied by rotations of the hydroxymethoxymethylene substituent about the С=С bond with the activation barrier ΔE_ZPE= 23.5 (gas) and 20.9 (CH₂Cl₂) kcal/mol. This reaction path is 18.6 kcal/mol more favorable in energy than transition of fulvene 1 to cyclopentadiene 2 with subsequent 1,5- sigmatropic hydrogen shifts in the five-membered ring.     

Synthesis and spectral luminescence properties of 2-aryl-5-methyl-1,3,4-oxadiazoles and zinc(ii) 2-(2-hydroxyphenyl)-5-methyl-1,3,4-oxadiazole complex

Russian Chemical Bulletin - 2-Aryl-5-methyl-1,3,4-oxadiazoles were synthesized by reflux of equimolar amounts of acyl hydrazides with triethyl orthoacetate in o-xylene. The obtained oxadiazoles,...     

3,3-Sigmatropic Shifts of Allyl Group Along Cyclopentadiene Ring Perimeter

Reversible non-degenerate 3,3-sigmatropic shifts of the allyl group along the perimeter of the five-membered ring occurring with energy barriers ΔG°≠ = 28.5–30.2 kcal/mol (o-dichlorobenzene-d4) have been detected in the allyl derivatives of 5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene by NMR method. Using DFT B3LYP/6-311++G(d,p) method, it has been shown that degenerate migrations of the allyl group in the related 5-allyl-1,2,3,4,5-pentamethoxycarbonylcyclopentadiene should occur via 3,3-sigmatropic shift through transition states with conformation of a six-membered ring (chair or boat, with close barriers ΔG°≠ = 27.4 or 27.7 kcal/mol, respectively). The simulated higher barrier of alternative 1,5-sigmatropic shifts of the allyl group (ΔG°≠ = 30.8 kcal/mol) indicates the energy preference of the migrations via 3,3-shifts.