Structural peculiarities of configurational isomers of 1‐styrylpyrroles according to 1Н, 13С and 15N NMR spectroscopy and density functional theory calculations: electronic and steric hindrance for planar structure

Comparative analysis of the ¹Н and ¹³С NMR data for a series of the E and Z‐1‐styrylpyrroles, E and Z‐1‐(1‐propenyl)pyrroles, 1‐vinylpyrroles and styrene suggests that the conjugation between the unsaturated fragments in the former compounds is reduced. This is the result of the mutual influence of the donor p–π and π–π conjugation having opposite directions. According to the NMR data combined with the density functional theory calculations, the Z isomer of 1‐styrylpyrrole has essentially a nonplanar structure because of the steric hindrance. However, the E isomer of 1‐styrylpyrrole is also an out‐of‐plane structure despite the absence of a sterical barrier for the planar one. Deviation of the E isomer from the planar structure seems to be caused by an electronic hindrance produced by a mutual influence of the p–π and π–π conjugation. The structure of the E isomer of the 2‐substituted 1‐styrylpyrroles is similar to that of the 2‐substituted 1‐vinylpyrroles. The steric effects in the Z isomer of the 2‐substituted 1‐styrylpyrroles result in the large increase of the dihedral angle between planes of the pyrrole ring and double bond. Copyright © 2013 John Wiley & Sons, Ltd.     

Polarity and Conformations of Phosphazacompounds in Solution

Abstract

A series of iminophosphoranes o-X-C₆H₄-N=PPh₃, where X=H(I),Me (II),Et (III),OMe(IV),OEt(V) were investigated by means of dipole moments method. Because of an orientation of aromatic fragment determines intramolecular interactions in the system (benzene ring - double N=P bond), the problem of internal rotation of N-C_ar bond is important. DM (exp.) of molecules (I-V), determined in dioxane are 4.30(I), 4.34(II), 4.53(III), 4.75(IV), 4.79 D(V), respectively.     

On pseudorandom numbers from multivariate polynomial systems

We bound exponential sums along the orbits of essentially arbitrary multivariate polynomial dynamical systems, provided that the orbits are long enough. We use these bounds to derive nontrivial estimates on the discrepancy of pseudorandom vectors generated by such polynomial systems. We generalize several previous results and in particular suggest a new approach that eliminates the need to control the degree growth of the iterations of these polynomial systems, which has been an obstacle in all previous approaches.     

On pseudopoints of algebraic curves

Clifford indices for semistable vector bundles on a smooth projective curve of genus at least four were defined in a previous paper of the authors. The present paper studies bundles which compute these Clifford indices. We show that under certain conditions on the curve all such bundles and their Serre duals are generated.     

Solid‐State Luminescence of Au?Cu?Alkynyl Complexes Induced by Metallophilicity‐Driven Aggregation

A new series of homoleptic alkynyl complexes, [{Au₂Cu₂(C₂R)₄}_n] (R=C₃H₇O ( 1 ), C₆H₁₁O ( 2 ), C₉H₁₉O ( 3 ), C₁₃H₁₁O ( 4 )), were obtained from Au(SC₄H₈)Cl, Cu(NCMe)₄PF₆, and the corresponding alkyne in the presence of a base (NEt₃). Complexes 1 – 4 aggregate upon crystallization into polymeric chains through extensive metallophilic interactions. The cluster that contains fluorenolyl functionalities, C₁₃H₉O ( 5 ), crystallizes in its molecular form as a disolvate, [Au₂Cu₂(C₂C₁₃H₉O)₄] ? 2 THF. The substitution of weakly bound THF molecules with pyridine molecules leads to the complex [Au₂Cu₂(C₂C₁₃H₉O)₄] ? 2 py ( 6 ), thus giving two polymorphs in the solid state. Such structural diversity is established through metal‐chain and hydrogen‐bond formation, which depends on the stereochemical characteristics of the organic ligands. More interestingly, this solid‐state structural arrangement affords good emission properties, such as intensity and spectroscopic profile, which are otherwise very weakly emissive in solution. Metallophilic aggregation of the {Au₂Cu₂} cluster units, as observed in the crystals, results in dramatic enhancement of the room‐temperature phosphorescence, thereby reaching a maximum quantum efficiency of 95 % ( 4 ). A theoretical approach further indicates a synergistic effect of the array of the metal chain upon aggregation, which greatly enhances the spin‐orbit coupling and, hence, the phosphorescence, thereby opening up a new direction in the field of aggregate‐enhanced emission.