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1.
Optical absorption and emission spectra are reported for single crystals of the cubic elpasolite Cs2NaSmCl6. The variable temperature spectra obtained at high resolution are assigned using energies and relative intensities. Transitions from the ground level, 6H to cystal fi levels of 6H-, 6F-, 4G-, 4F,, 4I, and 6P, are located and characterized. Intensity calculations are reported for magnetic dipole allowed transitions. The dominance of vibronic intensity in 6H→6F - and 6P, transitions is accounted for qualitatively through the ligand polarization model involving quadrupole metal (Sm3+)-ligand (Cl?) interaction mechanisms. The Eu″(6H)→E′(6H) Eu′(6F) no-phonon transition is postulated to be pure electric quadrupole allowed. The ground state magnetic moment is determined to be very small from magnetic circular dichroism (MCD) spectra.This study has led to the assignment of nearly all of the crystal field levels in the visible and IR region for Cs2NaSmCl6. A total of 27 such levels were identified, 17 from no-phonon transitions and the rest from vibronic transitions. The magnetic dipole intensity calculated using intermediate coupling Oh wavefunctions along with a crystal field analysis of the splitting pattern was used in the assignment of the levels. Vibronic bands were observed for all transitions and their vibrational symmetries were tentatively assigned. MCD data were used to determine the magnet moment of the ground state. 相似文献
2.
The conformational behaviour of the methylenemalonaldehyde fragment of the title compounds is characterized by solvent and temperture dependencies of 1J(O), 3J(HO,CO), 3J(HO,C), 4J(CO,CO) and 4J(CO,C) spin-spin couplings as well some (STO-3G) and semiempirical level Molecular orbital calculations. The conformational behaviour of the couplings is also discussed on the basis of some INDO/FPT calculations. The conformations of the two formyls are strongly correlated, the - arrangements being favored. The conformation of the Z-formyl is determined by the steric interaction with the aromatic nucleus. The conformations of the formyls are sensitive to solvent and substitution on the aryl. Approximate populations and couplings of the sites are derived. There is some evidence about the non-planarity of the methylenmalonaldehyde fragnent. Complex formation with Mg(C104)2 is reported. 相似文献
3.
J.L. Breton F. Camps J. Coll L. Eguren J.A. Gavin A.G. Gonzalez X. Martorell C. Miravitlles E. Molins J. Torramilans 《Tetrahedron》1985,41(15):3141-3146
A new heliangolide has been isolated from aerial parts of , and identified as (6,10)(3,3a,4,lla)-3a,5,8,11a--tetrahydro-4-acetoxy-3,6, 1O-trimethyl-2,9 (3, 4) -cyclodeca[b] furandione. The structural elucidation of the new compound, named heliangolidin, was carried out by spectral means (MS, IR, 1H and 13C NMR, and two dimensional 1H-13C chemical shift correlations) and X-ray diffraction analysis. 相似文献
4.
H.I.X. Mager 《Tetrahedron letters》1979,20(37):3549-3552
The pyrazine ring opening is proven by rearrangements leading to benzimidazoles , and . A 4a- to 10a-adduct isomerization ( → ) and the intermediacy of a carbonyl oxide are indicated by pyrimidine ring contractions into and , respectively. 相似文献
5.
tert-Butyl azidoformate () reacts with the conjugate bases of , , (R1 = R2 = CH3), and (R1 = CH3, R2 = H) to give products [, , , and , respectively] in addition to the expected N-(tert-butoxycarbonyl)indole derivatives. 相似文献
6.
The production of I(2P) in the photolysis of CH2I2 has been studied optoacoustically at excitation wavelengths between 365.5 and 247.5 nm. Bands found at 32200 and 47000 cm?1 correlate with I(2P) whilst those at 34700 and 40100 cm?1, which correlate with I(2P), give final 2P/2P ratios of 1.75 and 1.1, respectively, after curve crossing. 相似文献
7.
Felix H. Cano Concha Foces-Foces Manuel Bernabe Jesus Jimenez-Barbero Manuel Martin-Lomas Soledad Penades-Ullate 《Tetrahedron》1985,41(18):3875-3886
X-Ray and 1H N.M.R. studies on pyranoid rings 1,2--fused to dioxolane rings in acetylated -gluco- and --galactopyranose derivatives demonstrate that the configuration of the dioxolane ring influences the conformation of the pyranoid ring in the -gluco but not in the -galactopyranose series. The crystal structure of 3,4,6-tri--acetyl-1,2--(R)--(l-cyano-ethylidene)-α--glucopyranose () and 3,4,6-tri--acetyl-1,2--()-(1-cyano-ethylidene)-α--galactopyranose ()have been determined by X-ray analysis. Lattice parameters for are a=20.6021 (11), b=8.0438 (2), c=5.5541 (1) Å and β= 95.588 (3)° for a cell with P21 symmetry. These parameters for are a=20.3361 (7), b=10.0907 (2), c=18.9115 (5) Å, β =112.399 (2)°, C2, with two crystallographycally independent molecules. The conformation of the pyranoid ring in both compounds can be described as flattened 4C1 and that of the dioxolane ring as distorted E1. The importance of the torsion angles for describing problems of configuration is remarked and the use of relative configurational angles is stressed. The 1H N.M.R. spectra of and and 3,4,6-tri--acetyl-1,2-O-(S)- and (R)-ethylidene-α--glucopyranose ( and ), 3,4,6-tri-O-acetyl--1,2-O-(S)- and ()-ethylidene-α--galactopyranose ( and ), and 3,4,6-tri--acetyl-1,2--()-and ()-benzylidene-α--glucopyranose ( and ) have been analyzed by using iterative computer methods and N.O.E. measurements. The results indicate that the major solution conformation of the pyranoid ring of the derivatives in the -gluco series , and may be described as flattened 4C1 and that of and as 25. The major solution conformation of the pyranoid ring in all compounds in the -galacto series (,,,) may be described as flattened 41. 相似文献
8.
The synthesis of [O9,24] [2.1.2.1]metacyclophane-9-ene and of its dehydrogenation products^the new pyrenocyclophanes , , , and , is described; their structures are discussed in connection with their 1H-NMR-spectra. 相似文献
9.
The model tripeptide Boc-Gly-S-Ala-Aib-OMe () and the two monothiated analogues Boc-Gly(1ψ2CSNH)-S-Ala-Aib-OMe () and Boc-Gly-S-Ala(2ψ3 CSNH)-Aib-OMe () were synthesized. Peptide was obtained by thiation of using 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide, Lawesson's Reagent (LR), followed by deprotection of the Boc group and coupling with Boc-Gly-OH. Thiation of with LR regiospecifically transformed the protected tripeptide to the monothiated analogue . X-Ray diffraction analysis showed that the type-III β-turn formed by the reference peptide is preserved in the monothiated analogue ; conversely,the structure of the isomeric tripeptide is partially extended. 相似文献
10.
The details and principles of an apparatus built for measurements of fluorescence quantum yields and cascade-free lifetimes of open-shell cations are reported. These rely on the detection of coincidences between energy selected photoelectrons and undispersed photons. The results of such measurements for CO+2, COS+, CS+2 and N2O+ in selected vibrational levels of their excited states are presented. Non-unity fluorescence quantum yields are found for some vibronic levels of CO+2(), COS+ (), N2OP+() and a non-exponential decay is observed for CS+2(). The data yield the following values for the radiative lifetimes: CO+2() 124 ± 6 ns, CO+2() 140 ± 7 ns, COS+() 550 ± 50 ns and N2O+() 240 ± 12 ns. 相似文献
11.
Claudio Fuganti Piero Grasselli Giuseppe Pedrocchi-Fantoni 《Tetrahedron letters》1979,20(26):2453-2454
Feeding experiments with (4) [5-3H;5-14C]-leucine () and with the (4) [5-3H;2-14C]-isomer () show that incorporation into the isoprenylated tryptophan derivative echinuline (), produced by , involves, to a large extent, loss of the fragment enbodying the carbon atom at position 2 of the fed amino acid. 相似文献
12.
The chiral axis in the title glycine derivative has allowed its resolution into enantiomers: the barrier Δ G≠ for racemisation (rotation around the bond) is 26.2 Kcal mol?1. 相似文献
13.
Dialkylcarbodiimides, , react with iminium salts, , to afford the formal 1,1-diaminosubstituted 2-azaallenium salts . According to dynamic NMR measurements compounds must be regarded as alkylidene-guanidinium salts , undergoing a fast topomerization via a transition state with allene geometry (2G=265 = 45.9 ± 1 kJmol-1 for ) and a slower rotation around the peripheral C-N bonds (transition state ; 2G=290= 58.0 ± 1 kJmol-1 for ). 相似文献
14.
The acid catalysed reaction of 4-oxa-homoadamantan-5-one () with benzene yielded a mixture of 4a-phenyladamantan-2-one (), the equatorial isomer' () and 2-phenyl-2,4-o- benzenoadamantane () A plausible reaction pathway for the occurrence of . is put forward. The structure of , was deduced from spectroscopic data and reaction of the proposed intermediate 2,4a-diphenyladamantan-2-ol () with acid. 2,4-o-Ben-zenoadamantane () is prepared likewise. 相似文献
15.
13Cmr spectra show complete absence of scrambling of an 18O label in recovered after partial conversion to thereby precluding an -methylation mechanism for the bimolecular formation of from . 相似文献
16.
Condensation of 1,3-bis(trimethylsiloxy)-1-methoxybutadiene with the acid chloride 12 gave methyl olivetolate (). Condensation of with (+)-p-mentha-2,8-dien-1-ol gave methyl Δ1-tetrahydrocannabinolate () in 55% isolated yield. Alkaline hydrolysis of gave Δ-tetrahydrocannabinol (, Δ1-THC). The synthesis is patterned after the biogenesis of . 相似文献
17.
The 1H and 13C nmr spectra of , -9-oxobicyclo[3.3.1]nonane-2,4-dicarboxylic acid, 3, in DMSO-d6 or alkaline D2O, clearly show that it exists in a --conformation with carboxyl groups, thus being the first case of - preference of a bicyclo[3.3.1] nonan-9-one due to the presence of ,-2,4- substituents. 相似文献
18.
A practical synthesis of [Ph3CH2F]BF4? is reported two routes, fluorination of [Ph3CH2OH]BF4? with DAST or hydrolysis of the phosphoranium salt, [Ph3FPh3]Br?. 相似文献
19.
The conditions for the preparation and cyclisation of the title compounds are described. The stability of the intermediate lithio-thiacyclohexenes is shown to depend on the reaction conditions and the substituents R1-R4. The final products , and arise from via a [1.4] sigmatropic rearrangement, a [1.3]prototropic shift followed by a [2.3] sigmatropic rearrangement, or the elimination of lithium methanethiolate respectively. 相似文献
20.
EI mass spectra of -η4,η4-[3,6-bis(methylene)-1,4-cyclohexadiene]-bis=(tricarbonyliron) complexes , are reported. The fragmentation pathway is rationalized by assuming a rearrangement of the -bis(tricarbonyliron) complexes into the -isomers under electron impact. 相似文献