Photodegradation of aramids. II. Irradiation in air

A series of isomeric fully aromatic polyamides (aramids) were photodegraded in the presence of oxygen. Films and fibers of these aramids gave carboxylic acids as the major products when measured by infrared spectroscopy and potentiometric titration. These acids probably resulted from the oxygen interception of the radicals generated by photocleavage of the amide bonds. In contrast to results found upon irradiation in the absence of oxygen, carboxylic acid formation was accompanied by a rapid loss in molecular weight, and a decrease in useful mechanical properties. Quantum yields for carboxylic acid formation were ≤5.5 × 10^?5 mole/einstein and decreased along the aramid series roughly in agreement with increases in T_g. The photo-Fries rearrangement product was observed in aramid fibers irradiated in air, whereas no rearrangement product was seen in films irradiated in air.     

The phenomenon of conglomerate crystallization. XX. Spontaneous resolution in coordination compounds. XVIII.

The title compound, [cis-Co(en)₂(NO₂)₂](NO₂) (1), crystallizes in the polar, nonenantiomorphic, monoclinic space group, Cc, with lattice constants:a=9.198(2) Å,b=12.444(2),c=9.963(3), and=96.76(2)°;V=1132.39 ų andd(calc;Z=4) =1.860 g cm^–3. Thus, with NO_2– as the counteranion, [cis-Co(en)₂(NO₂)₂] crystallizes in a heterochiral lattice containing racemic pairs of cations. A total of 2699 data were collected over the range of 4°270°; of these, 1859 (independent and withI3(I)) were used in the structural analysis. Data were corrected for absorption (=15.465 cm^–1) and the relative transmission coefficients ranged from 0.9934 to 0.7112. Refinement was carried out for both lattice polarities and the finalR(F) andR _w (F) residuals were, respectively, 0.0242 and 0.0202 for (–––) and 0.0264 and 0.0243 for (+++). Thus, the former was selected as correct for our specimen.Unlike all previous X-ray diffraction studies of the structural properties of the cation [cis-Co(en)₂(NO₂)₂]⁺, which are found to have a pair of oppositely configured en rings [i.e., () or ()], we find that in1 the cations are in the lowest energy conformation and configuration; i.e., () or (). We attribute this change in configuration to the formation of strong interionic hydrogen bonds between nitrite anion oxygens and the axial—NH₂ hydrogens, which markedly weaken the intermolecular and intramolecular hydrogen bonds between ligand—NO₂ oxygens and the hydrogens of those same amine moieties. Thus, the nitrite anions behave exactly as nitrate anions, except that the hydrogen bonds found here are stronger than those formed by the latter. This is as expected since the negative charge is delocalized over two, instead of three, oxygens.     

Lanthanides in organic synthesis. Synthesis of bicyclicalcohols.

Lanthanide reducing agents have been found to effectively promote intramolecular alkylation reactions to provide the corresponding bicyclic alcohols in excellent yields.     

Carbon-13 n.m.r. characterization of indenyllithium in solution

¹³C N.m.r. chemical shifts obtained for indenyl- and cyclopentadienyllithium in several, mostly ethereal, solvents are presented. The chemical shift changes induced by varying the solvent are assumed to probe the actual π-electron density distribution, thus providing an insight into the structure of the ion-pair. The increase in the estimated π-electron densities obtained for the protonated aromatic carbons of indenyllithium by increasing the coordinating ability of the solvent gives evidence of a change of the ion-pair equilibrium towards solvent-separated species. The average chemical shifts for indenyl- and cyclopentadienyllithium were independent of the choice of solvent, a fact which supports the ion-pair model in all studied media.     

Ion Chromatographic Determination of Phosphorus in Eight U.S.G.S. Standard Rocks

Abstract

A method is described for the analysis of phosphorus in geological samples involving the decomposition of the sample with hydrofluoric acid in a quartz tube and the measurement of phosphate ion concentration using an ion chromatograph (Dionex 10) with an anion separator column (Wescan anion 269-001). The detection limit is between 0.05-0.5% P₂O₅ in the original sample. Multiple analyses of eight U.S.G.S. standard rocks yielded a relative standard deviation range between 2.37-16.67%. In excess of 15 samples can be analyzed in an 8 hour day.     

A special method of deformational correction in N.M.R. of molecules dissolved in liquid crystals

A simple method of deformational correction for the N.M.R. spectral parameters of molecules dissolved in liquid crystals is described. The method is applicable to the different isotopically substituted derivatives of the molecules belonging to the cubic point groups. Its validity is verified for the dipolar and quadrupolar couplings observed in the molecules CH₄, CD₄ and CH₃D dissolved in the liquid crystals Merck Phase IV, Merck ZLI 1167 and their mixtures.     

A special method of deformational correction in N.M.R. of molecules dissolved in liquid crystals

Abstract

A simple method of deformational correction for the N.M.R. spectral parameters of molecules dissolved in liquid crystals is described. The method is applicable to the different isotopically substituted derivatives of the molecules belonging to the cubic point groups. Its validity is verified for the dipolar and quadrupolar couplings observed in the molecules CH₄, CD₄ and CH₃D dissolved in the liquid crystals Merck Phase IV, Merck ZLI 1167 and their mixtures.     

Mass spectrometric determination of cadmium in i.a.e.a. fish solubles

The cadmium content of the I.A.E.A Fish Solubles [A-6 (1975)] was determined by the isotope dilution method. After dry-ashing and dissolution of the specimen, the cadmium was equilibrated with a known amount of ¹⁰³Cd spike, isolated by ion exchange, purified by dithizone extraction, and converted to the sulfide form in 1% H₃PO₄ solution. The CdS precipitate was loaded onto a baked single rhenium filament for mass spectrometric analysis. The ¹⁰³Cd/¹¹⁰Cd ratio was measured to compute the cadmium content of 0.278 ± 0.032 ppm (dry weight basis) in the Fish Solubles.     

Near-U.V. photolysis of pyrimidine heteroadducts in E. coli DNA

Abstract— The cytosine-thymine precursor of the U–T adduct is not subject to enzymatic photoreactivation, but can be eliminated directly from u.v.-irradiated E. coli DNA by exposure to wavelengths around 313 nm.     

N.m.r. determination of wax esters in marine lipids

The proton n.m.r. spectra of lipids containing triglycerides and wax esters dissolved in CDCl₃ are characterized by seven sets of signals. The areas of the signals of terminal methyl group and of methylene protons of both wax ester and triglyceride were integrated. These were used to calculate the content of wax esters in lipids or oils. The rapid n.m.r. procedure is directly usable for natural lipids containing as low as 3 mg of wax esters in 50-mg samples with an error of about 7%. The method described compares favorably with t.l.c. determination.     

E.S.R. investigation of helix inversion in induced cholesteric phases

The phenomenon of a reversible helix inversion in induced cholesteric mesophases caused by variation of the temperature has been investigated by E.S.R. spectroscopy using the nitroxide radical tempone as spin probe. Chiral esters of optically active (R)-(+)-2,2'-dihydroxy-1,1'-binaphthyl were added as dopants to the nematic mixture RO-TN 404. The inversion temperatures and the handedness of the helices were determined. In addition to the distortion parameter which is a measure of the helix pitch, order parameters and rotational correlation times of the spin probe were obtained from line-shape analyses.