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71.
Martin Petrzilka 《Helvetica chimica acta》1978,61(8):3075-3078
Starting from 5-chloro-2-pentanone ( 1 ) the naturally occurring 10-membered lactone phoracantholide J ( 8a ) has been synthesized as its racemate in a sequence of six steps (Scheme 2). Salient features of the syntheis include an internal selenium assisted acetal formation ( 4→5 ) and a stereoselective Claisen rearrangement ( 6→7→8 ). This general synthetic strategy offers an alternative approach towards the construction of macrocyclic lactones. 相似文献
72.
The fragmentation patterns of 24 substituted phenyltrifluoromethanesulfonates has been determined by exact mass and metastable transition measurements. The influence of the ring substituent(s) on the abundance of the [ArO]+ ions has been investigated at low energies and a new standard parameter for plotting against Hammett's ó constants is proposed. The direct loss of CF3SO3 from the molecular ion of 3,5-(diisopropyl)-phenyl-, 3,5-(dicyclopropyl)phenyl- and 3,5-di(α-methylcyclopropyl)-phenyl-methanesulfonate, and further observations on the fragmentation processes of these compounds are consistent with M.O. calculations on the ‘through bond’ stabilization of the [Ar]+ σ state by meta electron donor substituents. 相似文献
73.
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
74.
75.
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
76.
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
77.
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
78.
79.
Martin Macháček 《Journal of statistical physics》1987,47(5-6):949-952
We define mathematically a class of dynamical systems that exhibit relaxation corresponding to that observed in physical systems, and then show that this class is identical with the class ofK-mixing dynamical systems. 相似文献
80.
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