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181.
182.
(+)-Sesbanine was effectively synthesized from 4-methylnicotinonitrile and 1-malic acid. 相似文献
183.
Irradiation of α-bisulfenylated keto compounds in acetonitrile affords the cis-fused dihydrobenzothiophenes which are dehydrated to benzothiophenes in high yields. 相似文献
184.
The asymmetric total synthesis of cis, anti, cis-tricyclo[5,3,0,02,6]decane sesquiterpene β-bourbonene is described. The key (2+2) photocycloaddition was carried out applying the optically pure butenolide derivative as a chiral synthon. 相似文献
185.
186.
Summary Thermally stable anionic tetracarbonylcobalt complexes containing triheterocarbenium ions, [Co(CO)4]–[cation]+, have been synthesized by the ion exchange reaction of [Co(CO)4]–PPN+ with the corresponding carbenium ions. Similar molybdenum complexes containing cyclopentadienyl and carbonyl ligands were also prepared. The complexes were characterized by elemental analyses and by i.r. and n.m.r. spectroscopies. The ionic structures of the complexes are confirmed on the basis of their large electric conductivities. 相似文献
187.
Yoshihiro Takahashi Takashi Kitamura Kenji Uchida Masao Tomura 《Journal of luminescence》1980,21(3):269-275
Emission spectra and decay times of the fluorescence excited at the absorption edge region in pyrene crystals were measured. At liquid nitrogen temperature, the fluorescence under the excitation at 390 nm is considered as the excimer emission and its band peak shifts a little to the short wavelength in comparison with that of the excimer emission under the excitation at 360 nm. The emission decay times under the excitation at the 390 nm and 360 nm are about 155 ns and 180 ns, respectively, at liquid nitrogen temperature. The former decay time changes its value abruptly near 127 K. This abrupt change of the decay time may be due to the phase transition in pyrene crystals. 相似文献
188.
Treatment of 1,1-dichloroalk-1-enes with Cp2Ti[P(OEt)3]2 produced organotitanium species, which afford allenes on treatment with aldehydes and ketones. 相似文献
189.
We report spectroscopic evidence for the pressure-induced structural changes in B2O3 glass quenched from melts at pressures up to 6 GPa using solid-state NMR. While all borons are tri-coordinated at 1 atm, the fraction of tetra-coordinated boron increases with pressure, being about 5% and 27% in the B2O3 glass quenched from melts at 2 and 6 GPa, respectively. The fraction of boroxol ring species increases with pressure up to 2 GPa and apparently decreases with further compression up to 6 GPa. Two densification mechanisms are proposed to explain the variation of boron species with pressure. 相似文献
190.
Ohwada K Fujii Y Katsuki Y Muraoka J Nakao H Murakami Y Sawa H Ninomiya E Isobe M Ueda Y 《Physical review letters》2005,94(10):106401
The present resonant x-ray scattering has been performed on a monoclinically split single domain of NaV(2)O(5). The observation of a critically enhanced contrast between V(4+) and V(5+) ions has led us to the unequivocal conclusion of the charge-order pattern of the low-temperature phase of NaV(2)O(5) below T(c) = 35 K. In spite of the possible four types of configuration of the zigzag-type charge-order patterns in the ab plane (A,A',B and B'), the stacking sequence along the c axis is determined as the AAA'A' type by comparison with model calculations. 相似文献