Proton magnetic resonance spectra of thenyl derivatives—II. Chloromethylthiophenes and some dithienylmethanes

PMR spectra of thirty-eight chloromethylthiophene and seven dithienylmethane derivatives were observed at 60 or 40 MHz. The chemical shifts of methylene protons were 4·63 to 5·25 ppm for monosubstituted 2-chloromethylthiophenes and 4·37 to 4·56 ppm for monosubstituted 3-chloromethylthiophenes, respectively, with reference to TMS. Those for 2,2′ -dithienylmethanes, which have one substituent in each ring, were 4·12 to 4·34 ppm. These shifs are useful for determination of the positions of the methylene groups in the related compounds. The long-range coupling constants observed for methylene proton signals are also useful for the determination of the positions of substituents.     

Star-shaped polycyclic aromatics based on oligothiophene-functionalized truxene: synthesis,properties, and facile emissive wavelength tuning

A facile approach to soluble star-shaped oligothiophene-functionalized polycyclic aromatics based on truxene is developed in this Communication. The Suzuki coupling reactions afford the thiophene-containing polycyclic aromatics with long branches (about 2.1 nm length from the heart to the periphery) from truxene precursor with excellent yields. The unsubstituted alpha-positions of thiophene rings allow for efficient halogenation and for further functionalization. The investigation of proton NMR spectra indicates that the hexahexyl groups efficiently prevent the self-association through the arene-arene pi-stacking. Chemical shifts belonging to methylene groups move more upfield than do those of methyl groups. These chemical shift values (about 0.5-0.6 ppm) are quite lower than those of normal methyl and methylene groups. We also prepare a dendritic hyperbranched polymer P1 through FeCl3 mediated oxidative polymerizations. The photophysical properties of all compounds possessing good symmetry are investigated by UV-vis and emission measurement.     

Additive NMR chemical shift parameters for deshielded methine protons

The use of additive parameters for the prediction of NMR chemical shifts is widely practised. However, no correlations are available for highly deshielded methine protons. In this work, methine chemical shifts have been studied using both multiple linear regression analysis and Simplex function minimization in an effort to determine under what limiting circumstances the additivity of shift parameters can be expected to apply. As expected, it was not possible to explain satisfactorily all methine shifts with a single set of substituent parameters. However, if only the deshielded cases were considered (H—CXYZ, where at least two of the three groups X, Y, and Z are electron-withdrawing), a much better set of parameters could be determined. Using a data set of 440 of these deshielded methine shifts, involving 31 different substituents, a standard error of estimate of 0.20 ppm is found for protons spread between 3.0 and 7.5 ppm.     

THE CALCULATIOM OF CHEMXCAL SHIFTS IN SUBSTITOTED PYRIDINES

<正> The principle and method for the calculation of chemical shifts of substituted benzenes have been extended to calculation of the cheiiical shifts in substituted pyridines. We have set up a series of empirical parameters for calculation of the chemical shifts. The calculated results of 154 δ values frou 54 compounds show that the standard deviation between the calculated and the experimental values is 0 . 09 ppm. The combination of the coupling constants can be used to provide a criterion for the determination of molecular structure in substituted pyridines and to assign NMR parameters for the experiment of proton simulated spectra of substituted pyridines.     

THE CALCULATION OF CHEMICAL SHIFTS IN DISUBSTITUTED NAPHTHALENES

<正> The principle and method for calculating the chemical shifts of substituted benzenes have been extended to the calculation of chemical shifts in disubstituted naphthalenes. We have set up a series of empirical parameters for the calculation of chemical shifts. The calculated results of 439 8 values from 78 compounds show that the standard deviation between the calculated and the experimental values is 0.08 ppm. The combination of this calculation with that of the coupling constants can be used to provide a criterion .for the determination of molecular structure in disubstituted naphthalenes as well as to assign NMR parameters for the experiment of proton simulated spectra of disubstituted naphthalenes.     

The role of aromatic groups in the Tobey-Simon additivity rule for vinylic protons

The Tobey-Simon (additivity) rule for aromatic groups which was devised about 40 years ago has been found to need revision. The rule shows an aromatic group attached to a C==C double bond as causing a downfield chemical shift of a cis-related vinylic proton and a small upfield shift of a trans-related proton. A search of data in the recent literature has shown that this rule should apply mainly to monosubstituted phenyl groups and some polynuclear aromatics. In contrast with them, 2,6-disubstituted phenyl, 2,4,6-trisubstituted phenyl and 9-anthracenyl groups cause cis-related vinylic protons to resonate upfield of comparable trans-related protons. Further, the current rule for o-substituted phenyl groups has been found to be inaccurate. In writing a rule for aromatic groups, therefore, greater attention needs to be given to the diversity of effects that these groups have on chemical shifts of vinylic protons.     

Long-range relativistic heavy atom effect on 1H NMR chemical shifts of selenium- and tellurium-containing compounds

Previously unknown manifestation of heavy atom effect on the NMR chemical shifts of β- and γ-protons initiated by the relativistic effects of the tellurium and selenium atoms has been investigated in the representative series of selenium- and tellurium-containing compounds. To approve the four-component density functional approach to be the appropriate tool for the investigation of the heavy atom on light atom effect (HALA), the benchmark calculations of the proton chemical shifts have been performed at the CCSD level using comprehensively chosen locally dense basis set with taking into account solvent, vibrational, and relativistic corrections. A good agreement with the experimental data was achieved. The magnitudes of the relativistic HALA corrections to β- and γ-proton chemical shifts were found to vary in a wide range, namely from −3.08 ppm for the γ-proton of methyltelluraldehyde to 14.51 ppm for β-proton in benzotelluraldehyde.     

Carbon-13 and proton magnetic resonance studies of some carbonyl-bis-(amino acid esters)

A number of carbonyl-bis-(amino acid esters) have been examined by proton and carbon-13 nuclear magnetic resonance techniques. All but one of the compounds were synthesized with two chiral centers of like-configuration. In one series, the diastereotopic nonequivalence of isopropyl methyl groups attached to the asymmetric centers is apparent in both the proton and the carbon spectra, and the relative magnitude of the observed nonequivalence increases slightly with increasing ‘bulk’ of the neighboring ester groups. Carbon-13 chemical shifts are reported, and a linear correlation of Taft σ* inductive constants with ester carbonyl carbon chemical shifts and with amide proton chemical shifts (for a series in which only variation of the ester substituent occurs) is presented. In addition, the effect in terms of chemical shift differences of keeping the same ester group at the asymmetric centers while varying the other substituent group, is examined.     

Two-dimensional NMR studies of 2-substituted thioxanthene sulfoxides

2-Fluoro-, 2-chloro-, 2-bromo-, 2-methyl-, and 2-methoxythioxanthene have been prepared by borane reduction of the corresponding thioxanthone. The corresponding sulfoxides were prepared by m-chloroperoxybenzoic acid oxidation of these sulfides. Proton and carbon chemical shifts have been assigned to these thioxanthene sulfoxides with the aid of LROCSCM and SROCSCM experiments. Carbon chemical shifts in the unsubstituted rings occur at approximately 125 ppm (C5); 128 ppm (C6); 130 ppm (C7); 128 ppm (C8); and 36 ppm (C9). The methylene protons appears as AB doublets at approximately 4.2 and 3.8 ppm. All sulfoxides have the same, pseudo-equatorial geometry.     

The solvent effect on polar compounds containing acidic hydrogens

The effect of aromatic and non-aromatic solvents on the proton chemical shifts of 23 polar compounds has been determined. The protons which are activated by electron-withdrawing groups show large highfield shifts in benzene (relative to the isotropic solvents). Based on evidence provided by infrared data, the highfield shifts of the acidic protons in benzene solution are interpreted in terms of a model involving C? Hπ hydrogen bonding. This model successfully interprets the data reported previously for steroidal ketones. The same model can be extended to benzene solutions of other polar compounds containing strongly electron-deficient sites to which alkyl groups are attached. It is observed that the use of CCl₄ as a reference solvent in studies of benzene induced shifts may have greater significance, since these two solvents have similar dielectric constants.     

Accurate prediction of proton chemical shifts. I. Substituted aromatic hydrocarbons

Forty‐five proton chemical shifts in 14 aromatic molecules have been calculated at several levels of theory: Hartree–Fock and density functional theory with several different basis sets, and also second‐order Møller–Plesset (MP2) theory. To obtain consistent experimental data, the NMR spectra were remeasured on a 500 MHz spectrometer in CDCl₃ solution. A set of 10 molecules without strong electron correlation effects was selected as the parametrization set. The calculated chemical shifts (relative to benzene) of 29 different protons in this set correlate very well with the experiment, and even better after linear regression. For this set, all methods perform roughly equally. The best agreement without linear regression is given by the B3LYP/TZVP method (rms deviation 0.060 ppm), although the best linear fit of the calculated shifts to experimental values is obtained for B3LYP/6‐311++G**, with an rms deviation of only 0.037 ppm. Somewhat larger deviations were obtained for the second test set of 4 more difficult molecules: nitrobenzene, azulene, salicylaldehyde, and o‐nitroaniline, characterized by strong electron correlation or resonance‐assisted intramolecular hydrogen bonding. The results show that it is possible, at a reasonable cost, to calculate relative proton shieldings in a similar chemical environment to high accuracy. Our ultimate goal is to use calculated proton shifts to obtain constraints for local conformations in proteins; this requires a predictive accuracy of 0.1–0.2 ppm. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1887–1895, 2001     

Theoretical predictions of 31p NMR chemical shift threshold of trimethylphosphine oxide absorbed on solid acid catalysts

The 31P NMR chemical shifts of adsorbed trimethylphosphine oxide (TMPO) and the configurations of the corresponding TMPOH+ complexes on Br?nsted acid sites with varying acid strengths in modeled zeolites have been predicted theoretically by means of density functional theory (DFT) quantum chemical calculations. The configuration of each TMPOH+ complex was optimized at the PW91/DNP level based on an 8T cluster model, whereas the 31P chemical shifts were calculated with the gauge including atomic orbital (GIAO) approach at both the HF/TZVP and MP2/TZVP levels. A linear correlation between the 31P chemical shift of adsorbed TMPO and the proton affinity of the solid acids was observed, and a threshold for superacidity (86 ppm) was determined. This threshold for superacidity was also confirmed by comparative investigations on other superacid systems, such as carborane acid and heteropolyoxometalate H3PW12O40. In conjunction with the strong correlation between the MP2 and the HF 31P isotropic shifts, the 8T cluster model was extended to more sophisticated models (up to 72T) that are not readily tractable at the GIAO-MP2 level, and a 31P chemical shift of 86 ppm was determined for TMPO adsorbed on zeolite H-ZSM-5, which is in good agreement with the NMR experimental data.     

15N nuclear magnetic resonance spectroscopy. Natural abundance 15N NMR of monosubstituted indoles

¹⁵N chemical shifts of twenty-four substituted indoles have been determined in natural abundance (in organic solvents) using Fourier transform NMR. The overall chemical shift range is 27 ppm, with groups in the 2-, 3- and 5-ring positions showing the largest substituent effects. Substituents capable of resonance interaction with the indole nitrogen give shifts in the expected directions but they cannot be correlated with known substituent parameters. Compounds measured in DMSO give 0·2 to 10·2 ppm downfield shifts with respect to the same compound measured in CDCl₃. ¹³C NMR data for previously unreported compounds are also reported.     

Substituent effects on magnetic non- equivalence in acetals

The proton and ¹³C? H satellite spectra of five diethyl haloacetals have been analyzed and their spectral parameters obtained. The parameters for the ethoxy methylene protons indicate the extent of their magnetic nonequivalence. It has been found that these parameters are dependent on the degree of halogen substitution in the group Z, which is bonded to the central carbon atom, and correlate well with the corresponding group electronegativity values, a′ _z, proposed by Huheey. The parallel behavior of the methylenic J (C? H) and chemical shifts indicates that a primarily through-bond mechanism is responsible for propagation of both the electronic and symmetry effects observed. Transmission factors calculated from the spectral data agree with independent estimates reasonably well, thus supporting the conclusions reached here.     

Synthesis and physicochemical studies of some novel picrate derivatives

(1)H and (13)C NMR spectra were recorded for some novel picrate derivatives derived from some 3,3-methyl-2,6-diarylpiperidin-4-ones and 3-benzyl-2,6-diarylpiperidin-4-one. The difference in the chemical shift of equatorial methylene proton and axial methylene proton at C(5) [Δ = δ(eq)-δ(ax)] is highly negative which is in contrast to the value observed in the corresponding parent piperidin-4-ones and this is attributed to the syn 1,3-diaxial interaction between the axial N-H bond and axial hydrogen at C-5. The effect of protonation on the chemical shifts was studied in detail. The chemical shifts of the heterocyclic ring protons are influenced by the picrate anion. Solvatochromism of picrates were studied in detail. DFT calculations were carried out in order to find out the NBO analysis, HOMO-LUMO energies, MEP studies and hyperpolarisability behaviour. The electric dipole moment (μ) and the first-hyperpolarisability (β) value of the investigated molecules have been studied theoretically which reveal that the synthesized molecules have microscopic non-linear optical (NLO) behaviour with non-zero values.     

Lösungsmitteleffekte in Kernresonanzspektren gesättigter Kohlenwasserstoffe (III). Unterscheidung unpolarer und polarer Effekte bei Steroiden

Benzene-induced proton NMR. solvent shifts of methyl and methylene groups in 25 acyclic and cyclic saturated hydrocarbons have been studied. The dependence of magnitude and sign of these unpolar effects upon the molecular shape is again demonstrated. Solvent shifts in polar solutes (hydroxy- and keto-steroids) are shown to originate from a superposition of polar and unpolar effects. The implications for the interpretation of small solvent shifts in polar solutes are discussed.     

Carbon-13 NMR spectra of all the isomeric methyl hydroxy- and acetoxyoctadecanoates. Determination of chemical shifts by deuterium isotope effects

Carbon-13 NMR spectra of the 17 isomeric methyl hydroxyoctadecanoates and the corresponding acetate derivatives have been measured and chemical shifts assigned to most carbons. Sixteen specifically deuterated hydroxy esters, and their acetates, were employed to make unambiguous assignments from the deuterium isotope effects on the spectra. When substituents are separated from the ends of the chain by 2–3 methylene groups their effects are largely additive. Long range effects of the hydroxyl group were γ, +0.01; δ, ?0.09; ε, ?0.11; ζ, ?0.06; η, ?0.05; and θ, ?0.04 ppm, and of the acetate group were γ, ?0.20; δ, ?0.20; ε, ?0.16; ζ, ?0.11; η, ?0.08 and θ, ?0.07 ppm, showing that they extend across seven methylene groups.     

The solvent-induced shift in the proton NMR of some quinolizidine substituents

The proton chemical shift values for the methyl groups in the nine monomethylquinolizidines are determined in deuterochloroform and benzene solutions. This solvent change results in the shielding of all the methyl groups except those in 1(a)-and 3(a)-methylquinolizidine which become deshielded. These results are compared with those obtained earlier for equatoral and axial methyl and methylene groups attached to the quinolizidine systems in Nuphar alkaloids and related compounds.     

顺磁性镧系金属有机配合物的~1H核磁共振研究

顺磁类的核磁共振研究大多是简单化合物,偏重理论方面的研究,对镧系配合物曾有报道。由于这类样品对空气和湿气极为敏感,在国内外研究顺磁性~1H谱甚少。本文研究了含氯桥的醚基取代环戊二烯镧系配合物二聚体的~1H化学位移,线宽,弛豫时间T_1和磁化率,从中找出了顺磁类有机镧系配合物~1H NMR的规律。     

Hydrogen-bonding partner of the proton-conducting histidine in the influenza m2 proton channel revealed from (1)h chemical shifts

The influenza M2 protein conducts protons through a critical histidine (His) residue, His37. Whether His37 only interacts with water to relay protons into the virion or whether a low-barrier hydrogen bond (LBHB) also exists between the histidines to stabilize charges before proton conduction is actively debated. To address this question, we have measured the imidazole (1)H(N) chemical shifts of His37 at different temperatures and pH using 2D (15)N-(1)H correlation solid-state NMR. At low temperature, the H(N) chemical shifts are 8-15 ppm at all pH values, indicating that the His37 side chain forms conventional hydrogen bonds (H-bonds) instead of LBHBs. At ambient temperature, the dynamically averaged H(N) chemical shifts are 4.8 ppm, indicating that the H-bonding partner of the imidazole is water instead of another histidine in the tetrameric channel. These data show that His37 forms H-bonds only to water, with regular strength, thus supporting the His-water proton exchange model and ruling out the low-barrier H-bonded dimer model.