J. Nowicka-Scheibe

The [NHN]− homoconjugated anions: X-ray diffraction, IR and multinuclear MR studies

X-ray diffraction, IR and NMR studies are reported on chemically symmetric [NHN]− anions formed by 1,8-bis(4-toluenesulphonamido)naphthalene, 1,8-bis(trifluoroacetamido)naphthalene, 1,8-diamino-2,4,5,7-tetranitronaphthalene and di-4-nitroimidazolyl-5-sulphide after abstraction of a proton by means of the proton sponge (DMAN), and in the 2:1 adducts of 4,5-dicyanoimidazole and 2-amino-4,5-dicyanoimidazole with DMAN as well as in the conjugated tetrazole-tetrazolate anion. The anionic NHN− hydrogen bonds studied so far are markedly weaker as compared with NHN+ cationic ones of similar geometry. They are characterized by an asymmetric, in the scale of vibrations, H-atom localization in the bridge with the protonic (NHN)− band located usually in the region 2600–3000 cm−1. The δ1H value in acetonitrile of the bridge proton in [NHN]− anions studied until now is between 14.1 and 16.4 ppm, while that in protonated DMAN is 18.7 ppm. The studies on 15N chemical shift and 15N1H coupling constant yielded additional information on the symmetry of [NHN]− bridges and localization of the bridge H-atom.

Inelastic neutron scattering (INS) studies on 2,5-dihydroxy-1,4-benzoquinone (DHBQ).

Inelastic neutron scattering (INS) spectra of solid 2,5-dihydroxy-1,4-benzoquinone were measured and compared with IR and Raman data. The INS spectrum is very well reproduced in the region below 1000 cm(-1) by DFT calculations on the B3LYP/6-311++G** level using Gaussian and Climax programs. To get a better agreement one should take into account additional interactions of OH groups in the solid state leading to an increase of the gamma(OH) frequency and to a decrease of frequencies for modes in which the delta(OH) participates. The studies of the deuterated compound in IR enabled to correct the assignment of gamma(OH) vibrations. Highly asymmetric nu(OH) band observed in IR spectrum with sharp maximum at about 3300 cm(-1) is discussed in terms of a stochastic approach to the analysis of hydrogen bonded systems.

Structural studies on (3,4,8,9)-dibenzo-2,7-dioxa-5,10-diaza[4.4.4]propellanes (DDDP)

Abstract The methyl and nitro derivatives of (3,4,8,9)-dibenzo-2,7-dioxa-5,10-diaza[4.4.4]propellanes P2, P3, P7 and P9 were synthesized. The X-ray diffraction studies showed that 16,20-dinitro derivative (P7) crystallizes in non-centrosymmetric Pcn2 space group making this crystal to be promising in non-linear optics. The geometry of molecules is discussed in relation to the intramolecular interaction and charge distribution. Very helpful appeared from this point of view the 13C NMR spectra. In packing of molecules an important role play the N–H⋯O and C–H⋯O hydrogen bonds reflected both in the crystal structures and IR spectra.

Low temperature investigations of dynamic properties in l-leucine – chloranilic acid complex

Inelastic neutron scattering (INS) and infra-red (IR) spectroscopy methods were used for determination of dynamic structure of l-leucine - chloranilic acid complex. A theoretical dynamic pattern calculated by the density functional theory (DFT) method for periodic boundary conditions accompanied the experimental ones. Normal modes in the vibrational spectra were defined and described. The characteristic presence of the Hadžis trio enriched by numerous submaxima is observed in the wavenumber range 3200-800 cm-1. Bands assigned to CH3 torsion vibrations in the leucine cation were observed at 231 cm-1 and 258 cm-1 in the INS spectrum. Temperature-dependent far-infrared spectra in the temperature range 9 K-290 K were obtained. Vibrational bands were analyzed as a function of temperature. Activation energies for reorientational motion of CH3 and CH2 groups were determined by means of the band shape analysis performed for torsional and twisting vibrations of these groups. The estimated energy is equal to Ea = 2.7 ± 0.2 kJ/mol and Ea = 2.17 ± 0.12 kJ/mol for CH3 and CH2 groups, respectively. A phase transition at about 130 K in the l-leucine - chloranilic acid complex was observed.

Easy Access to cis-3-(Benzoxazol-2-yl)cyclopentanecarboxylic Acids from Camphorquinone and o-Aminophenols via an Unexpected Opening of Camphor Ring

Abstract An unexpected formation of cis-1,2,2-trimethyl-3-(benzoxazol-2-yl)cyclopenta-necarboxylic acids was observed as the result of an oxidative C-C bond cleavage of the camphor ring in the intermediate imine during the condensation reactions between camphoroquinone and o-aminophenols conducted under open air conditions. Supplemental materials are available for this article. Go to the publishers online edition of Synthetic Communications® to view the free supplemental file. GRAPHICAL ABSTRACT