N‐alkoxypyridinium salts as coinitiators in radical polymerization: Synthesis and Photochemical Properties

A few N‐alkoxypyridinium salts are developed as photoinitiators for efficient polymerization reactions. They are characterized by absorption properties below 300 nm, and generate alkoxy radicals on UV‐Vis light exposure. The squarylium dye was used as a blue‐light photosensitizer. Polymerization results are correlated with the photochemistry of N‐alkoxypyridinium salts. The quenching of the excited singlet state of squarylium dye by pyridinium salt and the formation of the semioxidized species of squaraine suggests an electron transfer from an excited dye to a coinitiator, and that the resulting oxygen‐centered radical initiates the polymerization process. The chemical mechanism was investigated by steady state photolysis and nanosecond laser flash photolysis experiments. Photoinitiating activity of new photoinitiators for initiation of polymerization of trimethylolpropane triacrylate in the UV‐blue light region was compared with photoinitiating ability of selected commercially available initiators. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2840–2850     

Organosulphur compounds-XXXVIII Axial preference of a 2-dimethoxyphosphoryl substituent in 1,3,5-trithiane

¹H-NMR studies and X-ray analysis indicate that 2-dimethoxyphosphoryl-1,3,5-trithiane exists both in solution and in the crystal in a chair conformation with the dimethoxyphosphoryl group at C-2 being axial.     

Crystal structure of the keto-enamine form of (+) (1S,2S)-2-(2-hydroxybenzylidene)amine-1-phenyl-1,3-propanediol

The title compound crystallizes in the orthorhombic space group P2₁2₁2₁, withZ=4,a=6.068(1)Å,b=10.922(1)Å, andc=21.713(2)Å. The compound is the chiral ligand of a copper complex used as an enantioselective catalyst. It crystallizes from methanol in the keto-enamine form, though the enol-imine isomer predominates in the solution. Most N-salicylideneamines studied by X-ray are enol-imines. The two tautomeric forms may interchange through anintramolecular hydrogen bond and the distances between non-H atoms in the resulting cyclic –O–H...N=C–C=C- or –C=O...H–N–C=C- fragment may be misleading, so that H atom position is the crucial factor for determination of the proper tautomeric form.     

Eyring parameters of dehydration processes

Thermogravimetry was used in the study of the kinetics of dehydration of MnSO₄·5H₂O, CuSO₄·5H₂O and 3CdSO₄·8H₂O under static air atmosphere. The values of the kinetic and thermodynamic parameters for each stage of thermal dehydration were calculated from α(T) data by using the integral method, applying the Coats-Redfern approximation. The best model for all stages of dehydration is random nucleation model F1. The dependencies of enthalpy on entropy of activated complexes for different kinetic models were described. The linear relation was calculated between the Gibbs energy of activated complexes and the maximum dehydration rate temperature for analysed dehydration processes.     

Vibrational spectra and stereochemistry of mono- and polysaccharides. IV. α-methyl-d-glucoside, α-methyl-d-galactopyranoside,and α-methyl-d-mannopyranoside

The IR and Raman spectra of α-methyl-D-glucoside (αMDG), α-methyl-D-galactoside (αMDGal), and α-methyl-D-mannoside (αMDM) are compared. The main distinctions between these spectra have been interpreted using experimental and theoretical data on the frequencies and modes of normal vibrations and on the potential energy distributions over particular bonds and atomic groups of the substances under investigation. Spectral characteristics that are determined by different configurations of C−O (CH) groups attached to C2 and C4 atoms and different conformations of C6H₂O6H fragments have been revealed. It has been established that replacement of hydroxyls at C1 with methoxy groups significantly increases the number of frequencies of normal vibrations that are localized mostly in the C1C2 bonds (particularly in αMDGal). For the αMDGal molecules with axial C4O4 groups, the number of frequencies of normal vibrations that show predominant contributions of these groups of PED is smaller. For the αMDM molecules, in which the conformation of CH₂OH groups (with respect to rotation around the C5C6 bonds) differs from that in αMDG and αMDGal molecules, most vibrations are localized in the C6O6 bonds rather than in the C5O5 bonds. This fact is very important in correlating the vibrational spectra and structural properties of mono- and polysaccharides. B.I. Stepanov Institute of Physics, Belarus Academy of Sciences. V. Tshebyatoski Institute of Low Temperatures and Structural Studies, Polish Academy of Sciences. Translated fromZhurmal Struktumoi Khimii, Vol. 36, No. 3, pp. 456–466, May–June, 1995. Translated by I. Izvekova     

Polarised IR and Raman spectra of monoglycine dihydrogenphosphate single crystal

Polarised Raman, IR and FIR spectra of the monoglycine dihydrogenphosphate (glycinium dihydrogenphosphate) single crystal samples are presented and discussed with respect to the crystal structure on the basis of oriented gas model approximation. The IR and FIR spectra were measured by specular reflection method and spectra of an imaginary part of the refractive indices were computed by the Kramers-Kronig transformation. The polarisation properties of the internal vibrations of the glycinium cation, H₂PO₄¹⁻ anion and hydrogen bonds are predicted and compared to the experimentally determined.