An X-ray study of some 2,3-diphenyltetrazolium salts

An X-ray diffraction study is reported for three molecules of salts containing a cation with a positive charged 2,3-diphenyltetrazolium ring. The results confirm aromatic structure of the tetrazole ring and the delocalization of charge on the whole molecules of the cations. The molecular geometry obtained is compared with that for free mesoionic 2,3-diphenyltetrazoles which have already been studied and the ring parameters do not reveal significant differences. But is shows that the geometry of the (NNO)^– exocyclic group is changed as a result of alkylation. Compound I C₁₃H₁₂N₅Cl, P2₁/a,a=16.934(4),b=6.575(1),c=26.121(4) Å, =108.15(2)°, II C₁₄H₁₃N₆OI, P3₁2,a=10.774(3),c=12.821(4) Å, IV C₂₆H₂₀N₈Cl₂, C2/c,a=22.316(4),b=6.6903(7),c=20.437(3) Å, =92.51(1)°.     

Nucleophilic SN2 displacements on penicillin-6- and cephalosporin-7- triflates; 6β-iodopenicillanic acid,a new β-lactamase inhibitor

Triflate or nonaflate esters of alkyl 6α (or β) hydroxypenicillanates are substituted (with inversion) by the soft nucleophiles iodide, bromide, chloride, azide, arylselenoxide,¹ thiocyanate, thiols, and thiolacids; carbon nucleophiles fail. Methoxide (hard) attacks the lactam bond, opening both rings to give a known¹¹ 1,4 thiazine. Iodide substitutes 7α-trifloxycephalosporins, giving 7β-iodocephalosporins.     

The assignment of signals in the nitrogen NMR spectra of polycyclic diazines

¹⁵N Nitrogen screening data are reported for some polycyclic azines and compared with previous results where available. INDO/S parameterized screening calculations for cinnoline and quinazoline help to decide between alternative nitrogen assignments. Nitrogen solvent shifts of several ppm are reported for all of the molecules studied.     

P and N solid-state nuclear magnetic resonance spectroscopic study of some monophospha-λ-azenes

³¹P Cross-polarization magic-angle spinning nuclear magnetic resonance (CP-MAS NMR) spectra of eight monophospha-λ⁵-azenes were measured at room temperature. Three of these compounds, with 2-OH substituents, are in principle capable of taking part in the equilibrium process. However, only the open form, tautomer A, is found in the present study. ¹⁵N CP-MAS NMR spectra support the results. The most shielded component of the ³¹P chemical shift tensor lies in the direction of the P=N bond.     

Use of RP-TLC to Determine the log P Values of Isomers of Organic Compounds

Selected pairs of isomeric organic compounds—oleic acid and elaidic acid, lauryl acetate and ethyl laurate, α-naphthol and β-naphthol, benzo[e]pyrene and benzo[a]pyrene, safrole and isosafrole, 1,6-diazaphenanthrene and 4,6-diazaphenanthrene, and (1R)-(–) fenchone and camphor—have been separated by reversed-phase thin-layer chromatography (RP-TLC). The partition coefficients were calculated by different theoretical procedures. A new method is proposed for calculation of partition coefficients on the basis of experimental R_F values.     

14N and 13C NMR of tautomeric systems of mercapto- and amino-pyridines

Nitrogen chemical shifts are shown to provide a means of estimating equilibrium compositions of tautomeric systems of mercapto- and amino-derivatives of pyridine. Carbon chemical shifts can afford only qualitative information about such equilibria.     

Effect of Temperature on the RF of Porphine and its Metal Complexes in Normal and Reversed-Phase TLC

JPC – Journal of Planar Chromatography – Modern TLC - Porphine and its complexes with Cu(II), Ni(II), and Zn(II) have been separated by adsorption and partition TLC. In adsorption TLC...     

An NMR study of hydrogen bonding in some azo dyestuffs

The ¹H, ¹³C, and ¹⁵N NMR data reported for compounds 1–4 show that in DMSO solutions all of them exist in the azo form only and do not participate in the azo–hydrazoimine equilibrium. The NMR data for compounds 1 and 2 show the presence of a weak hydrogen bond for the non-protonated forms, between N10 and the 2-NHCH₃ proton. All compounds have also been studied in TFA solutions in which they are protonated. The site of protonation of 1, 2 and 3 is determined to be at N10 in TFA solutions. These results are supported by some ab initio GIAO-CHF molecular orbital calculations.     

Measuring surface area of airborne titanium dioxide powder agglomerates: relationships between gas adsorption,diffusion and mobility-based methods

Inhalation toxicology studies generally use the Brunauer, Emmett, and Teller (BET) gas adsorption method to measure total surface area of particles whereas occupational exposures are more readily measured by real-time mobility-based surface areas or active surface area measured with diffusion charger-based instruments. Three surface area measurement methods were studied: filter-based inert gas adsorption (BET method), diffusion charging, and mobility-based methods. The goal of the project was to investigate and develop a correlation between the measurement methods. The experimental design consisted of measuring surface area in a series of five trials for each of two powder types, fine and ultrafine titanium dioxide with primary particle sizes of 440 and 20 nm, respectively, and two aerosol concentrations. Diffusion charger instruments tended to underestimate the total particle surface area measured by the BET, but were well correlated with mobility-based surface areas obtained from a scanning mobility particle sizer. Filter-based gas adsorption methods and diffusion charging methods provide different but valuable information on total and active surface areas of particles, respectively. Results indicate they should not be used as predictors of one another.     

A metastable electron trap in plastically deformed silicon

We communicate on an unusual feature of the DLTS spectrum of plastically deformed n-type silicon. In the cooling mode the DLTS signal at 240 K suddenly jumps nearly to zero. We interpret this effect as an entropy driven metastability of the deepest deformation-induced electron trap.Dedicated to H.-J. Queisser on the occasion of his 60th birthday