Global fittings of NNO and NNO vibrational-rotational line positions using the effective Hamiltonian approach

An effective Hamiltonian built up to sixth order in the Amat-Nielsen ordering scheme describing all rovibrational energy levels in the ground electronic state and containing in explicit form all resonance interaction terms due to the approximate relations between harmonic frequencies ω₁≈2ω₂ and ω₃≈4ω₂ was applied to model the observed rovibrational line positions (collected from the literature) of ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O isotopologues of nitrous oxide. For ¹⁴N¹⁵N¹⁶O, 124 effective Hamiltonian parameters were fitted to near 28 000 observed line positions covering the 0.8-8860 cm⁻¹ spectral range. The RMS of the weighted fit is 0.00126 cm⁻¹ and dimensionless standard deviation is 1.48. For ¹⁵N¹⁴N¹⁶O, 121 effective Hamiltonian parameters were fitted to more than 31 000 observed line positions covering the same spectral interval. The RMS of the weighted fit is 0.00185 cm⁻¹ and dimensionless standard deviation is 1.85. In both cases the models describe all available line positions with precision compatible to the measurement uncertainties. A number of local resonance perturbations was found and discussed. Among these perturbations there are interpolyad resonance Coriolis interactions. A comparison of HITRAN-2008 data with the calculations based on the fitted models is presented.     

Assignment of the 1H and 13C Spectra of 5-Methylthio-4H-1-(p-R1-phenyl)-3a-(p-R2-phenyl)-3a,4-dihydro (1,2,4) oxadiazolo(4,5-a), 1,5-benzodiazepines using 2D NMR Spectroscopy.

The ¹H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic enviroment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the ¹H and ¹³C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported.     

Assignment of the 1H and 13C Spectra of 5-Methylthio-4H-1-(p-R1-phenyl)-3a-(p-R2-Phenyl)-3a, 4-dihydro (1,2,4) oxadiazolo(4,5-a), 1, 5-benzodiazepines Using 2D NMR Spectroscopy

The ¹H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic environment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the ¹H and ¹³C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported.     

Natural Abundance 17O NMR Study of Substituted α,α,α-Trifluoromethoxybenzenes

Natural abundance ¹⁷O NMR chemical shift data for meta- and para-substitued α,α,α-trifluoromethoxybenzenes recorded in acetonitrile at 75° C are reported. The ¹⁷O NMR signals for the trifluoromethoxy compounds are deshielded by greater than 65 ppm compared to analogous methoxy compounds. A quantitative relationship between ¹⁷O NMR chemical shifts for the trifluoromethoxy and methoxy benzenes is reported.     

Quantitative Analysis of Acetazolamide in Solid Dosage Forms with 1H-Nmr Spectroscopy

A rapid and specific proton magnetic resonance spectroscopic method was developed for determining acetazolamide in tablets. Maleic acid was used as the internal standard and DMSO-d₆ served as the NMR solvent. the concentration of drug per unit dose was calculated from the integration values for the resonance signals of acetazolamide at 2.14 ppm and maleic acid at 6.20 ppm. the method using commercial products gave comparable results of those obtained by the method of USP XXIII.     

A 13C-NMR Study of Some 9-Ahinoacridines and Their Cations in Relation with Tautomaric Problems

¹³C-NMR chemical shifts have been measured for some 9-aminoacridine derivatives, substituted on positions 9 and 10, in DMSO and for some related salts in D₂O. The results are discussed with regard to amino/imino tautomerism, structure of the cations, and slow rotation about a formal C-N double bond.     

Photoinduced energy transfer from the triplet state of naphthalene moiety in the Tb/Eu complexes of a specially designed naphthalene cryptand

The paper reports time-resolved emission and energy transfer (ET) studies of metal ion complexes of a specially designed rigid macrocyclic naphthalene cryptand (L) under different conditions. Complex formation of L with Li⁺ and H⁺ causes an appreciable increase in singlet state quantum yield and lifetime of L implying photoinduced electron transfer (PET) from the cryptand moiety to naphthalene unit in the free L. The system exhibits photoinduced ET at 77 K in its Tb³⁺ and Eu³⁺ complexes with either NO₃⁻¹ or Cl⁻¹ as counter-anion. The extent of ET is higher for the Tb³⁺ complex as compared to that for the Eu³⁺ complex. In both Tb³⁺ and Eu³⁺ complex, the NO₃⁻¹ ions influence the relative orientation of donor (L) and acceptor (Ln³⁺) more in favour of ET than the Cl⁻¹ ions. The rate constants for the ET from the naphthalene moiety of L to the acceptor (Ln³⁺) have been evaluated at 77 K. The results suggest ET from the triplet state of naphthalene using an exchange mechanism. The ground state geometries of the system L and its complexes with Li⁺, Cs⁺ and Tb³⁺ have been determined using DFT methods to interpret our results.     

Correlations in 11B NMR spectra of dihalo derivatives of bis(1,2-dicarbollyl)cobalt(III)

In the ¹¹B NMR spectra of dihalo derivatives of bis(dicarbollyl)cobalt(III), we have identified a correlation between the ¹¹B NMR chemical shifts of substituted boron atoms and boron atoms found in other positions on the carborane skeleton. We have observed an increased shielding effect for fluorine atoms (compared with other halogens), manifested in an upfield shift of the ¹¹B NMR signals for antipodal and trans boron atoms. For the fluorine-containing compound Bu₄N⁺ [8,8′-F₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻, we propose the following sequence of electron density transfer: B(8) → {B(6) and B(10)} → B(4, 7). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 547–549 (cont.), July–August, 2006.     

Sub-barrier fission fragment angular distributions for the system19F+232Th

The measurements of fission fragment angular distributions for the system¹⁹F+²³²Th have been extended to the sub-barrier energies of 89.3, 91.5 and 93.6 MeV. The measured anisotropies, within errors are nearly the same over this energy region. However, the deviation of the experimental values of anisotropies from that of standard statistical model predictions increases as the bombarding energy is lowered.     

NMR Studies of Crowded Diels–Alder Adducts of Phencyclone with N‐(2,6‐Dialkylphenyl)maleimides. Hindered Rotations and Magnetic Anisotropy

Abstract

Phencyclone, 1, reacted with N‐(2,6‐dimethylphenyl)maleimide, 2a; with N‐(2,6‐diethylphenyl)maleimide, 2b; and with N‐(2,6‐diisopropylphenyl)maleimide, 2c, respectively, to yield the corresponding Diels–Alder adducts, 3a–c. The adducts were extensively characterized by NMR (7 T) at ambient temperatures using one‐ and two‐dimensional (1D and 2D) proton and carbon‐13 techniques for assignments. Slow exchange limit (SEL) spectra were observed, demonstrating slow rotations on the NMR timescales, for the unsubstituted bridgehead phenyl groups [C(sp³)–C(aryl sp²) bond rotations] and for the 2,6‐dialkylphenyl groups [N(sp²)–C(aryl sp²) bond rotations]. Substantial magnetic anisotropic shifts were seen in the adducts. For example, in the N‐(2,6‐dialkylphenyl) moieties of the adducts, one of the alkyl groups is directed “into” the adduct cavity, toward the phenanthrenoid portion, and these “inner” alkyl proton NMR signals were shifted upfield. Thus, in CDCl₃, the “inner” methyl of adduct 3a exhibits a proton resonance at ?0.13 ppm, upfield of tetramethylsilane (TMS); the “inner” ethyl group signals from 3b appear at 0.026 ppm (CH₂, quartet), and ?0.21 ppm (CH₃, triplet); and the “inner” isopropyl group from 3c is seen at ?0.06 ppm (methine, approx. septet) and ?0.39 ppm (CH₃, doublet). Proton NMR of the crude N‐(2,6‐dialkylphenyl)maleamic acids (used as precursors of the maleimides, 2a–c) exhibited two sets of AB quartet signals, suggesting possible conformers from hindered rotation in the amide groups about the HN–C?O bonds.     

15N216O在1650-3450 cm-1的高分辨红外光谱

采用傅里叶变换红外光谱仪记录了富含¹⁵N₂¹⁶O同位素的一氧化二氮样品在1650-3450 cm^-1波段的高分辨振转光谱,得到了该同位素分子超过7300吸收谱线位置的实验值,经分析实验精确度好于5.0×10^-4 cm^-1. 基于有效哈密顿量模型预测和带带转动分析,确定了所有吸收线的归属;获得了29个新吸收带的振转光谱参数,并优化了其他44个吸收带的光谱参数值. 并且发现有效哈     

Natural Abudance 17O NMR Studies of Thiol Esters and Related Analogs

Natural abundance ¹⁷O NMR data for a series of thiol esters and related analogs are reported. The carbonyl signal of the thiol esters range from 463 ppm to 514 ppm; these values are downfield of their oxygen analogs by ca. 150 ppm. A linear relationship between the ¹⁷O NMR chemical shift of the thio-compounds and their oxo-analogs is observed.     

17O and 13C NMR Studies of Isobenzopyrylium Salts

¹³C and ¹⁷O NMR chemical shifts for a series of isobenzopyrylium salts are reported. The oxygen signal range from 300 to 270 ppm as a double bonded carboxylic oxygen, From the ¹⁷O and ¹³C data valuable informations on the conjugative and substituent effects of isobenzopyrylium salts were obtained.     

13C NMR Chemical Shifts of Heterocycles: Empirical Substituent Effects in 5-Halomethylisoxazoles

Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the ¹³C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R¹) = H, alkyl or phenyl, C-4 Substituent (R²) = H, alkyl, and C-5 substituent (R³) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The ¹³ C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm.     

Solid State C NMR of 30-Crown-10 Ether and 30-Crown-10.4H2O

The ¹³C NMR solution spectra of 30-crown-10 ether and its tetrahydrate show only one resonance at all accessible temperatures. In contrast, the solid state ¹³C NMR spectrum of the 30-crown-10.4H₂O shows two resonances in the ratio of 4:1, separated by 1.2 ppm. In the case of 30-crown-10 itself, six resolvable ¹³C resonances in the ratio of 4:1:1:2:1:1 are observed in the solid with an overall chemical shift dispersion of 5 ppm. The remarkably different spectral behavior of these two systems in the solid state is discussed in terms of the torsional environments of the crystallographically unique carbons and the results of GIAO calculations of isotropic ¹³C shieldings for simpler model compounds. Results of dipolar dephased ¹³C CPMAS spectra indicate that 30-crown-10 does not undergo a large amplitude molecular motion, in contrast to earlier results for 18-crown-6. Only a small amount of residual intensity is found in the dipolar dephased spectrum of 30-crown-10.4H₂O, indicating that it also is relatively rigid in the solid.     

Line Intensities in the ν6 Fundamental Band of CH3Br at 10 μm

Fourier transform spectra have been obtained at 296 K at a resolution of 0.002 or 0.004 cm^-1 depending on the pressure range. Line positions and intensities of CH₃⁷⁹Br and CH₃⁸¹Br belonging to the fundamental band ν₆ were measured and analyzed between 890 and 1080 cm^-1. A total of 2896 (2838) line positions with J≤60 and K≤6 was fitted with a root-mean-square deviation of 0.00028 (0.00021) cm^-1 for CH₃⁷⁹Br and CH₃⁸¹Br, respectively, within the experimental accuracy. The fit to 316 (312) measured intensities yielded values of the dipole moment derivatives of both isotopes with a standard deviation of 5% to be compared to an experimental uncertainty equal to 6% or better. A prediction of the line positions and intensities has been generated for atmospheric purposes with all lines from 820 to 1120 cm^-1 with intensities greater than 10^-5 cm^-2 atm^-1.     

A High-Precision Carbon-13 Shift Thermometer for the Temperature Range 100–300 K

The first carbon-13 shift thermometer for the temperature range of 100–300 K is based on the very rapid equilibration of a pair of semibullvalene valence tautomers. The temperature dependence of the equilibrium constant is reflected in strongly temperature-dependent shift differences Δδ between averaged signals, e.g.,d(Δδ)/dT= 0.051 ppm K⁻¹at 300, 0.087 ppm K⁻¹at 200, and 0.175 ppm K⁻¹at 110 K for the quaternary carbon atoms C2 and C6. At 37 temperaturesT, which were measured with calibrated platinum resistance thermometers, shift differences Δδ were taken from nondecoupled carbon-13 spectra recorded from solutions of 1 in mixtures of chlorodifluoromethane and deuterated dimethyl ether without spinning. The least-squares fit of these Δδ vsTdata to a polynomial equation of the fourth degree (Eq. [5],r²= 0.9999) allows the calculation of temperatures from measured shift differences with a standard deviation of 0.46 K and an estimated error of about 1 K. The heating effects of WALTZ-16 decoupling and the influence of solvents on Δδ are investigated. A comparison with existing NMR thermometers demonstrates the superior performance of the new carbon-13 shift thermometer with respect to precision and the accessible temperature range.     

Magnitudes and Orientations of the N Chemical Shift Tensor of [1-N]-2′-Deoxyguanosine Determined on a Polycrystalline Sample by Two-Dimensional Solid-State NMR Spectroscopy

The magnitudes and orientations of the ¹⁵N chemical shift tensor of [1-¹⁵N]-2′-deoxyguanosine were determined from a polycrystalline sample using the two-dimensional PISEMA experiment. The magnitudes of the principal values of the ¹⁵N chemical shift tensor of the N1 nitrogen of [1-¹⁵N]-2′-deoxyguanosine were found to be ς₁₁ = 54 ppm, ς₂₂ = 148 ppm, and ς₃₃ = 201 ppm with respect to (¹⁵NH₄)₂SO₄ in aqueous solution. Comparisons of experimental and simulated two-dimensional powder pattern spectra show that ς_33N is approximately collinear with the N–H bond. The tensor orientation of ς_33N for N1 of [1-¹⁵N]-2′-deoxyguanosine is similar to the values obtained for the side chain residues of ¹⁵N_ε1-tryptophan and ¹⁵N_π-histidine even though the magnitudes differ significantly.     

C, N CPMAS NMR and GIAO DFT calculations of stereoisomeric oxindole alkaloids from Cat's Claw (Uncaria tomentosa)

Oxindole alkaloids, isolated from the bark of Uncaria tomentosa [Willd. ex Schult.] Rubiaceae, are considered to be responsible for the biological activity of this herb. Five pentacyclic and two tetracyclic alkaloids were studied by solid-state NMR and theoretical GIAO DFT methods. The ¹³C and ¹⁵N CPMAS NMR spectra were recorded for mitraphylline, isomitraphylline, pteropodine (uncarine C), isopteropodine (uncarine E), speciophylline (uncarine D), rhynchophylline and isorhynchophylline. Theoretical GIAO DFT calculations of shielding constants provide arguments for identification of asymmetric centers and proper assignment of NMR spectra. These alkaloids are 7R/7S and 20R/20S stereoisomeric pairs. Based on the ¹³C CP MAS chemical shifts the 7S alkaloids (δ C3 70–71 ppm) can be easily and conveniently distinguished from 7R (δC3 74.5–74.9 ppm), also 20R (δC20 41.3–41.7 ppm) from the 20S (δC20 36.3–38.3 ppm). The epiallo-type isomer (3R, 20S) of speciophylline is characterized by a larger ¹⁵N MAS chemical shift of N4 (64.6 ppm) than the allo-type (3S, 20S) of isopteropodine (δN4 53.3 ppm). ¹⁵N MAS chemical shifts of N1–H in pentacyclic alkaloids are within 131.9–140.4 ppm.     

High sensitivity cw-cavity ringdown and Fourier transform absorption spectroscopies of CO2

The absorption spectrum of ¹³CO₂ has been recorded by cw-cavity ringdown spectroscopy with a new set up based on fibered DFB lasers. By using a series of 31 DFB lasers, the spectrum of carbon dioxide could be recorded in the 6130-6750 cm⁻¹ region with a typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹. The spectrum has also been recorded between 4400 and 8500 cm⁻¹ with a Fourier transform spectrometer associated with a multi-pass cell (maximum path length of 105 m). The new observations obtained both by FTS and CRDS represent a significant extension of the available data. For instance, more than 4000 line positions were measured and assigned in the CRDS spectrum while only 232 line positions are listed in the HITRAN database. Altogether, the band by band analysis has led to the determination of the rovibrational parameters of 65, 7, and 24 bands for the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O, and ¹⁶O¹³C¹⁸O isotopomers, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model, the new observed line positions were gathered with the data available in the literature to refine the set of effective Hamiltonian parameters of the ¹³C¹⁶O₂ isotopic species. The refined set of 96 effective Hamiltonian parameters reproduces more than 14 650 line positions of ¹³C¹⁶O₂ with an RMS=0.002 cm⁻¹. A detailed comparison with the line positions retrieved from Venus spectra and the line list provided by HITRAN is also presented and discussed.