Studies in mass spectrometry. IV—Fragmentation of aryltriflates. Substituent effects on [ArO]+ ion abundances: Looking for a best suited electron energy in the steady state approach. Experimental evidence for the ‘through bond’ stabilization of aryl cations by meta electron donor Substituents

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.     

Structural Aspects of the Enantioselectivity of Tartrates with α-Amino-alcohol Salts. Part II. Crystal structures of (1R, 2S)-norephedrine hydrochloride and (1R, 2R)- norpseudoephedrine hydrochloride

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.     

A Highly Stereoselective Synthesis of C(11)-Functionalized Aromatic Steroids by an Intramolecular Benzocyclobutene-Olefin -Cycloaddition. Preliminary Communication

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).     

Nonlinear intensity dependence of the rate coefficient in unimolecular reactions induced by monochromatic infrared radiation

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.     

Borel fibrations and G-spaces

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.     

Symbolic dynamics for the renormalization map of a quasiperiodic Schrödinger equation

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.     

CHEMICALLY MODIFIED PHOTOSYNTHETIC BACTERIAL REACTION CENTERS: CIRCULAR DICHROISM, RAMAN RESONANCE, LOW TEMPERATURE ABSORPTION, FLUORESCENCE AND ODMR SPECTRA AND POLYPEPTIDE COMPOSITION OF BOROHYDRIDE TREATED REACTION CENTERS FROM Rhodobacter sphaeroides R26

Abstract— Reaction centers from Rhodobacter sphaeroides have been modified by treatment with sodium borohydride similar to the original procedure [Ditson et al., Biochim. Biophys. Acta 766 , 623 (1984)], and investigated spectroscopically and by gel electrophoresis.
(1) Low temperature (1.2 K) absorption, fluorescence, absorption- and fluorescence-detected ODMR, and microwave-induced singlet-triplet absorption difference spectra (MIA) suggest that the treatment produces a spectroscopically homogeneous preparation with one of the 'additional' bacteriochlorophylls being removed. The modification does not alter the zero field splitting parameters of the primary donor triplet (^TP870).
(2) From the circular dichroism and Raman resonance spectra in the1500–1800 cm^-1 region, the removed pigment is assigned to Bchl_M, e.g. the "extra" Bchl on the "inactive" M-branch.
(3) A strong coupling among all pigment molecules is deduced from the circular dichroism spectra, because pronounced band-shifts and/or intensity changes occur in the spectral components assigned to all pigments. This is supported by distinct differences among the MIA spectra of untreated and modified reaction centers, as well as by Raman resonance.
(4) The modification is accompanied by partial proteolytic cleavage of the M-subunit. The preparation is thus spectroscopically homogeneous, but biochemically heterogenous.     

Donor—acceptor interactions of substituted benzenes with molecular chlorine and carbon disulfide

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/?R_CICI) 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.     

Analytical applications of infra-red spectroscopy : The behaviour of the oxinates of niobium,tantalum and associated elements

The behaviour of the oxinates of niobium, tantalum and associated metals in the infra-red region was studied and a method developed for the determination of niobium and tantalum. Vanadium caused no interference, but other heavy metals, such as molybdenum, manganese and cobalt, which interfered were removed by preliminary treatment when the method was applied to the determination of niobium and tantalum in steels.