Additions of enantiopure alpha-sulfinyl carbanions to (S)-N-sulfinimines: asymmetric synthesis of beta-amino sulfoxides and beta-alphamino alcohols

The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported.     

Thermodynamics of deformation of an isolated polymer chain

Summary Deformation-dependent change in internal energy of a polymer chain affects also conformational entropy as a result of dependence of statistical characteristics upon the distribution of rotational isomers in the chain. Formulas describing deformation-dependent internal energy (distribution of rotational isomers), free energy and length of statistical segment have been derived using a model of rotational isomers, and assuming non-Gaussian conformational statistics. Example computations have been performed for polyethylene. The computations show decrease in the fraction of gauche isomers with increasing deformation, and the decrease is stronger for shorter chains, especially for the chains composed of less than 10³ C-C bonds. Corrections related to the non-Gaussian statistics and finite molecular weight lead to lower fraction of the gauche component in the chain. Fraction of gauche isomers in a deformed polyethylene chain has been calculated numerically byAllegra andAvitabile (10) using a method of matrices proposed byFlory (11). Although the authors (10) received qualitatively comparable results with our results, they discussed the subject for Gaussian chains in terms of different measure of chain deformation, 1, which does not show clearly the effect of the chain length. Calculations presented in this paper provide analytical formulas for the deformation-dependent thermodynamic and statistical characteristics of a deformed chain macromolecule with non-Gaussian statistics and finite molecular weight. As a result of the decrease of gauche isomers the length of statistical segment increases with increasing chain deformation, and it increases stronger for shorter chains. Temperature effect on the behaviour of a deformed chain macromolecule is also discussed. General formula for the elastic force and local stress tensor have been derived.With 4 figures     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Widths and shifts of HF vibration-rotation absorption lines induced by pressure of rare gases

Widths and shifts of the HF vibration-rotation absorption spectrum, induced by the pressure of rare gases, have been calculated using the Kolb-Griem-Baranger theory, for the pure rotation, 0–1, and 0–2 bands. Agreement between the calculated and experimental widths is good in general, but the calculated shifts, though having a qualitatively correct m-dependence for the most part, exceed the experimental values by a factor of 1·3-2·0. Isotropic effects are included to all orders, leading to three major consequences: (1) a criticism is made regarding one of the assumption underlying Anderson's approximation number two, (2) a reason is provided for the differences in widths of R and P branch lines of the same ∣m∣ within a given band, and (3) the previously unexplained increase in widths with increasing ∣m∣ in the 0–2 band with xenon is explained.     

Spin-singlet clusters in the ladder compound NaV2O5

The space group of alpha(')-NaV2O5 turns below T(c) = 34 K from Pmmn with all V sites equivalent, into Fmm2 with three independent vanadium sites per layer. This is incompatible with models of charge ordering into V4+ and V5+. Our structure determination indicates that the phase transition consists of a charge ordering with three distinct valence states, formally V4+, V4.5+, and V5+. The singlet formation is not associated with dimerization on the spin ladder, but with the formation of spin clusters. Finally, we ascribe the quadrupling of the c axis to the large polarizability of the V2O5 skeleton.     

Dependence of pulser driving responses on electrical and motional characteristics of NDE ultrasonic probes

Acoustic performance in ultrasonic transmitters can be improved by means of a suitable electrical driving response and matching/tuning networks. It is important to predict this electrical response, but doing so is not easy because it departs notably from the nominal pattern with the loading probes. In practice, the analysis of HV pulser spikes in NDE applications requires fairly complex models in the transient regime and, in addition, non-linear problems could arise, especially in the case of tuned transmitters. In this paper, the most relevant influences of loading characteristics of NDT ultrasonic probes on the pulser electrical driving responses are evaluated in time and frequency domains. Conventional pulse generators and typical NDE pulsers are considered. Driving responses are analysed across commercial ultrasonic probes and, alternatively, across similar purely electrical loads. Distinct influences on pulser responses from electrical and motional sections of the probes are identified. All these aspects are studied on the basis of experimental and computer results.     

The theory of non-linear molecular orientation and stress in polymer fluids

Non-linear stress, and orientation characteristics for polymer fluids (melts, solutions) composed of chain macromolecules of finite length have been derived. Freelyjointed chains with inverse Langevin statistics have been assumed, and their behaviour in potential hydrodynamic fields analyzed. Numerical calculations have been performed for uniaxial extensional flow in a wide range of flow rates (and stresses). In the range of small stresses, orientation is a linear function of stress. At higher stresses, orientation factor levels off, asymptotically approaching unity.Flow orientation characteristics significantly differ from those derived from affine deformation of polymer networks. This difference is a natural consequence of constraints imposed by network junctions on chain deformation.This work is dedicated to Professor Hanns-Georg Kilian on his 60th birthday in appreciation of his contribution to Polymer Physics.     

Effects of diffusion-controlled association in kinetic model of crystal nucleation in external orienting field

Translational and rotational diffusion equation of orientable single elements in external orienting potential field is used to discuss effective rate of association and dissociation during cluster growth. First and second harmonic terms of orientation-dependent potential energy of single elements are taken into consideration. Tolerance angle accounting for orientational limitations for association is introduced.Effective rate of association of single elements is derived with first-order correction for the effects of orienting potential. Net rate of cluster growth depends on orientation in the field, and it is controlled by longrange diffusion (rotational and translational) of single elements. Influence of diffusion is higher, the narrower the tolerance angle and the faster the association.At slow association, long-range diffusion does not influence the process, the growth of a cluster is controlled by thermodynamic, orientation-dependent potential of the species involved in the process.Effective rate constants of association and dissociation, as well as effective concentration of single elements are derived as functions of orientation angle in the field.The Fokker-Planck equation is proposed for the distribution of cluster size in external orienting potential, with the effects of finite translational and rotational diffusion of single elements, for the case of non-polar clusters.