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21.
Enantioselective host-guest complexes between α-amino-alcohol salts and chiral tartrates can not be crystallised up to now. To study structural aspects of their enantioselectivity, crystal structures of the components were determined. Norephedrine was used as a reference guest α-amino-alcohol. (1R, 2S)-Norephedrine hydrochloride (monoclinic, space group P21 Z = 4, a = 8.455, b = 10.331, c = 12.570 Å, β = 107.45°) and (1R, 2R)-norpseudoephedrine hydrochloride (monoclinic, space group P21 Z = 2, a = 5.493, b = 8.052, c = 11.986 Å, β = 104.62°) both adopt M-synclinal conformations with respect to the ammonium and hydroxy groups. Rather short intramolecular N…?O distances indicate interaction between ammonium and hydroxy groups. 相似文献
22.
23.
The racemic cis-anti-trans-steroids 9 to 11 have been synthesized in a highly stereoselective manner starting from 4-methoxybenzocyclobutene carboxylic acid via the key step 8 → 9 . (cf. Scheme 2). 相似文献
24.
Martin Quack 《Chemical physics letters》1979,65(1):140-145
It is shown that essentially incoherent, stepwise one-photon transitions arising in dense multilevel structures of polyatomic molecules irradiated with monochromatic coherent infrared radiation can give rise (under specified conditions) to a more than proportional intensity dependence of the steady-state rate coefficient in unimolecular reactions induced by monochromatic infrared radiation. 相似文献
25.
Martin Fuchs 《manuscripta mathematica》1987,58(3):377-380
Considering discrete groups G only, we present an elementary proof of the familiar equivalence of the category of G-spaces (with maps equivariant up to homotopy) and the category of Borel fibrations over BG. 相似文献
26.
27.
28.
Martin Casdagli 《Communications in Mathematical Physics》1986,107(2):295-318
A rigorous analysis is given of the dynamics of the renormalization map associated to a discrete Schrödinger operatorH onl
2(), defined byH(n)=(n+1)+(n–1)+Vf(n)(n), whereV is a real parameter,f is a certain discontinuous period-1 function, and
is the golden mean. The renormalization map forH is a diffeomorphism,T, of 3, preserving a cubic surfaceS
V
. ForV8 we prove that the non-wandering set of the restriction ofT toS
v
is a hyperbolic set, on whichT is conjugate to a subshift on six symbols. It follows from results in dynamical systems theory that the optimally approximating periodic operators toH have spectra which obey a global scaling law. We also define a set which we call the pseudospectrum of the operatorH. We prove it to be a Cantor set of measure zero, and obtain bounds on its Hausdorff dimension. It is an open question whether the pseudospectrum coincides with the spectrum ofH. 相似文献
29.
Sokoloff MD Anjos JC Appel JA Bracker SB Browder TE Cremaldi LM Elliott JR Escobar CO Estabrooks P Gibney MC Hartner GF Karchin PE Kumar BR Losty MJ Luste GJ Mantsch PM Martin JF McHugh S Menary SR Morrison RJ Nash T Ong P Pinfold J Purohit MV Raab JR Santoro AF Sidhu JS Sliwa K Souza MH Spalding WJ Streetman ME Stundia AB Witherell MS 《Physical review letters》1986,57(24):3003-3006
30.
Roy Edward Bruns Paul Martin Kuznesof James Elton Moore 《Journal of Molecular Structure》1975,29(2):211-223
CNDO molecular orbital calculations have been performed to analyze donor—acceptor interactions between molecular chlorine and benzene, toluene, mesitylene and hexamethylbenzene and the, as yet, unreported chlorine—hexafluorobenzene and carbon disulfide—benzene pairs. The stabilization energy and the dipole moment and its derivative (?p/?RCICI) calculated for the benzene—chlorine complex are in good agreement with the estimated experimental values. The trends in the experimental stabilization energies and the Cl-Cl vibrational frequencies with increasing methyl substitution appear to be well reproduced by the calculations. The charge transferred from the benzene donor is polarized toward the outer chlorine atom or sulfur atom. For hexafluorobenzene-chlorine the direction of electronic charge polarization is reversed from that of the benzene and methylbenzene complexes. The calculated results are discussed within the framework of Muliiken's simplified resonance theory for complexes. 相似文献