Homo- and methano[60]fullerenes with chiral attached moieties--1H and 13C NMR chemical shift assignments and diastereotopicity effects

(1)H and (13)C NMR chemical shift predictions of homo- and methano[60]fullerenes containing chiral centers in attached fragment were made using the two-dimensional NMR technique (HH COSY, (1)H-(13)C HSQC and HMBC) and the quantum chemistry GIAO calculation method in the PBE/3ζ approach. The influence of a chiral substituent on the (13)C chemical shifts of diastereotopic fullerene carbons was estimated by comparing the calculated and experimental (13)C NMR spectra. The resonances of the fullerene carbons in α-, β- and δ-positions relative to the position of the substituent exhibit the greatest diastereotopic splitting.     

1H-, 31P- and 13C-NMR spectra of some 2-arylsulphonylamido-2-thiono-5-methyl-1,3,2-dioxaphospholanes

Some 2-arylsulphonylamido-2-thiono-5-methyl-1,3,2-dioxaphospholanes (1), containing two chiral centres, give NMR spectra in which splittings of the ¹H and ¹³C signals of the 5-methyl substituent and of the ³¹P signal indicate that they exist in an approximately 70:30% ratio of two racemic mixtures, Z and E respectively, diastereomeric to each other. These splittings were invariably observed for compounds 1a, containing a monosubstituted sulphonylamido group (Y = H) and various substituents at position 4′ of the aryl group, X = H, CH₃, OCH₃, F, CI and Br. The methylenic protons in position 4 of the phospholane ring are diastereotopic and therefore magnetically non-equivalent. Benzene-induced shifts were measured for the Z isomers of compounds 1a, X = H, F and for compound 1b, containing an N-disubstituted sulphonylamido group (Y = CH₃) and X = H; the tentative interpretation of these shifts places the more shielded diastereotopic methylene proton on the same side of the ring as the 5-methyl substituent. The H? P and H? H coupling constants indicate that the preferred conformation of the dioxaphospholane ring should be a ‘twisted envelopey’ shape with the 5-methyl substituent in the equatorial position.     

A carbon-13 NMR study of the ion pair structure of the dibenzo[b,f]pentalene dianion

The ¹H and ¹³C NMR chemical shifts of dibenzo[b, f]pentalene and its 5,10-dimethyl derivative are presented and compared with those of the corresponding dilithium dianions. As probed by the relative ¹³C NMR chemical shifts, the charge distribution within the dianion system is clearly dependent on the actual ion pair state. This condition is demonstrated by varying the solvent and temperature. The polarization of charge towards the pentalene carbons, i.e. the preferred cation positions, is observed on going to tight ion pair conditions. Further support for this model is gained from ⁷Li NMR. The limitations of the use of ¹H and ¹³C NMR chemical shifts to measure charge distributions within anion systems are discussed.     

13C NMR STUDY OF SUBSTITUENT EFFECTS IN 1,2,4-OXADIAZOLE AND 1,2,4-THIADIAZOLE DERIVATIVES

¹³C chemical shifts of C═N, C═O and C═S carbons of 3,4-disubstituted-1,2,4-oxadiazole-5-ones(thiones) and 3,4-disubstituted-1,2,4-thiadiazole-5-ones have been determined in CDCl₃ solution. Exceptionally good Hammett correlations of ¹³C NMR chemical shifts of these carbons with σ were obtained. The negative ρ values observed (inverse substituent effects) indicate π-polarization of the C═N, C═O and C═S bonds. As expected, the long distance C═O and C═S ¹³C chemical shifts were found less susceptible to substituent-induced electronic changes.     

Hydroacridines: Part 30. 1H and 13C NMR spectra of 9‐substituted 1,2,3,4,5,6,7,8‐octahydroacridines and of their N‐oxides

The ¹H and ¹³C NMR chemical shifts of 1,2,3,4,5,6,7,8‐octahydroacridine, 12 of its 9‐substituted derivatives, and of the corresponding N‐oxides were determined, assigned, and discussed in terms of 9‐substituent effects and effects of N‐oxidation. A good linear correlation was found between the ¹³C chemical shifts of the aromatic carbons in octahydroacridines and those of respective carbons in the corresponding N‐oxides. Copyright © 2009 John Wiley & Sons, Ltd.     

13C Pulse fourier transform NMR of menthol stereoisomers and related compounds

¹³C NMR spectra of menthol stereoisomers have been determined. The correlations of chemical shifts of these ring carbons with those of stereoisomeric 2-isopropylcyclohexanols are examined. Observed chemical shifts of 1-Me carbons are compared with those predicted from the chemical shifts of stereoisomeric 1-methyl-4-t-butylcyclohexanes. ¹³C NMR spectra of menthyl acetates, and cis and trans p -menthanes have also been examined.     

13C NMR spectroscopic studies of the behaviors of carbonyl compounds in various solutions

¹³C NMR spectroscopic studies were performed for carbonyl compounds having a hydroxyl group, a carboalkoxy group, an acetoxy group, or a carboxyl group in various solvents with different polarities for observation of their behaviors of ¹³C NMR chemical shifts of carbonyl carbons in solutions. It was found that the chemical shifts of the carbonyl carbons in ¹³C NMR have good correlation with the empirical parameter for solvent polarities, E_T^N, depending on the structures. Inter- or intramolecular hydrogen bonding and dipolar-dipolar interactions appear to play a key role in this observation.     

1H and 13C NMR spectra of Strychnos alkaloids: Selected NMR updates

The PBE0/pcSseg-2//pcseg-2 calculations of ¹H and ¹³C NMR chemical shifts were performed for a classical series of 12 Strychnos alkaloids (except for the earlier studied parent strychnine), namely akuammicine, isostrychnine, rosibiline, tsilanine, spermostrychnine, diaboline, cyclostrychnine, henningsamide, strychnosilidine, strychnobrasiline, holstiine, and icajine. It was found that the calculated ¹H and ¹³C NMR chemical shifts show markedly good correlations with available experimental data, as characterized by a mean absolute error of 0.22 ppm for the range of 8 ppm for protons and 1.97 ppm for the range of 180 ppm for carbons. Complementarily, the present results provide essential NMR update and fill a gap in the NMR data of this distinguished group of vitally important natural products.     

Observation of Diastereotopic Signals in 15N NMR Spectroscopy

The first example in the literature of a compound showing anisochronous ¹⁵N atoms resulting from diastereotopicity is described. Racemic 1,3‐dimethyl‐2‐phenyloctahydro‐1H‐benzimidazole was prepared and studied by ¹H, ¹³C and ¹⁵N NMR spectroscopy. If convenient conditions were used (monitored by theoretical calculations of ²J_N‐H spin–spin coupling constants), two ¹⁵N NMR signals were observed and corresponded to the diastereotopic atoms. GIAO/density‐functional calculations of chemical shifts were not only in good agreement with the experimental values but also served as prediction tools. This study suggests that ¹⁵N NMR spectroscopy could be used to probe chirality.     

Determination of the orientational ordering of 4′-cyanophenyl-4-alkylbenzoates by 13C NMR

Abstract

The orientational ordering of three 4′-cyanophenyl-4-alkylbenzoates (with number of carbons in the alkyl chain, n = 6,7 and 8; hereafter abbreviated as n-CPBs) has been investigated by ¹³C NMR. The order parameters of different molecular segments in the nematic phase of the n-CPBs were determined by the two-dimensional technique of separated local field (SLF) spectroscopy combined with off-magic-axis, variable-angle spinning (VAS) of the sample. The carbon-13 chemical shifts for each carbon nucleus in these compounds were determined by slowly spinning the sample parallel to the applied magnetic field. The order parameters obtained from SLF/VAS studies are linearly related to the corresponding anisotropic carbon-13 chemical shifts. These results provide a convenient way to obtain the order parameters for other homologous members of this liquid crystal series by direct measurement of only their carbon-13 chemical shifts in conjunction with the observed linear relationship between order parameters and chemical shifts.     

Electronic effects in the cyclopentadienyl ring. The 13C NMR spectraof monosubstituted ferrocenes

The chemical shifts of C(2,5) and C(3,4) carbons in the ¹³C NMR spectra of monosubstituted ferrocenes have been assigned using deuterium labelling. An analogy is observed between the shielding of C(2,5) and C(3,4) carbons of ferrocene derivatives and ortho- and para-carbons of benzene derivatives withthe same substituents. Electron-density distribution in the cyclopentadienyl ring is discussed on the basis of ¹³C NMR data.     

The 1H and 13C NMR chemical shifts of Strychnos alkaloids revisited at the DFT level

The density functional theory calculation of ¹H and ¹³C NMR chemical shifts in a series of ten 10 classically known Strychnos alkaloids with a strychnine skeleton was performed at the PBE0/pcSseg-2//pcseg-2 level. It was found that calculated ¹H and ¹³C NMR chemical shifts provided a markedly good correlation with experiment characterized by a mean absolute error of 0.08 ppm in the range of 7 ppm for protons and 1.67 ppm in the range of 150 ppm for carbons, so that a mean absolute percentage error was as small as ~1% in both cases.     

13C chemical shifts of symmetrically substituted biphenyls: Unambiguous signal assignment for the carbons ortho and para to an aryl group

The natural abundance ¹³C NMR spectra of 2,2′-dimethyl-, 2,2′-dimethoxy- and 2,2′-dihydroxybiphenyls, and a series of 2,2′-dimethoxy-5,5′-disubstituted biphenyls were recorded. Unambiguous signal assignments of the carbons ortho and para to an aryl ring in biphenyls were made by selective deuteration and/or the graphical method for ¹H single frequency off-resonance decoupled spectra. Contrary to the reported assignments, it was shown that the signal for C-6 in 2,2′-dimethylbiphenyl clearly appears at lower field than that for C-4. The signals for the ortho carbons (C-6) of 2,2′-dimethoxy-5,5′-disubstituted biphenyls generally appeared at lower fields than those for the para carbons (C-4). The validity of applying deuterium isotope shifts to the assignments of ¹³C chemical shifts of di- and tetra-substituted biphenyls is also discussed.     

Experimental (FT-IR, FT-Raman, H, C NMR) and theoretical study of alkali metal 2-aminonicotinates

The influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of 2-aminonicotinic acid (2-ANA) was studied by the methods of molecular spectroscopy. The vibrational (FT-IR, FT-Raman) and NMR (¹H and ¹³C) spectra of 2-aminonicotinic acid and its alkali metal salts were recorded. Characteristic shifts and changes in intensities of bands along the metal series were observed. The changes of chemical shifts of protons (¹H NMR) and carbons (¹³C NMR) in the series of studied alkali metal 2-aminonicotinates (2-AN) were observed too.Optimized geometrical structures of the studied compounds were calculated by the B3LYP method using the 6-311++G** basis set. Aromaticity indices, atomic charges, dipole moments and energies were also calculated. The theoretical chemical shifts in ¹H and ¹³C NMR spectra and theoretical wavenumbers and intensities of IR and Raman spectra were determined. The calculated parameters were compared to the experimental characteristics of the studied compounds.     

Quantum‐chemical analyses of aromaticity,UV spectra,and NMR chemical shifts in plumbacyclopentadienylidenes stabilized by Lewis bases

We carried out a series of zeroth‐order regular approximation (ZORA)‐density functional theory (DFT) and ZORA‐time‐dependent (TD)‐DFT calculations for molecular geometries, NMR chemical shifts, nucleus‐independent chemical shifts (NICS), and electronic transition energies of plumbacyclopentadienylidenes stabilized by several Lewis bases, (Ph)₂(^tBuMe₂Si)₂C₄PbL₁L₂ (L₁, L₂ = tetrahydrofuran, Pyridine, N‐heterocyclic carbene), and their model molecules. We mainly discussed the Lewis‐base effect on the aromaticity of these complexes. The NICS was used to examine the aromaticity. The NICS values showed that the aromaticity of these complexes increases when the donation from the Lewis bases to Pb becomes large. This trend seems to be reasonable when the 4n‐Huckel rule is applied to the fractional π‐electron number. The calculated ¹³C‐ and ²⁰⁷Pb‐NMR chemical shifts and the calculated UV transition energies reasonably reproduced the experimental trends. We found a specific relationship between the ¹³C‐NMR chemical shifts and the transition energies. As we expected, the relativistic effect was essential to reproduce a trend not only in the ²⁰⁷Pb‐NMR chemical shifts and J[Pb‐C] but also in the ¹³C‐NMR chemical shifts of carbons adjacent to the lead atom. © 2014 Wiley Periodicals, Inc.     

13C-NMR-Spektren isomerer Diazaphenanthrene

The ¹³C chemical shifts of eleven isomeric diazaphenathrenes (1.5-? 1.10-, 2.7-, 4.5-? 4.7-, and 5.6-DAP) have been determined and iteratively assigned by means of comparison with suitable model compounds. The data obtained (132 points) were used to test the relationship between ¹³C chemical shifts and HMO charge densities. The best correlation with a standard deviation S(E) = 4.8 ppm was found for the chemical shifts, relative to phenanthrene, of tertiary carbons. The different slopes for correlations of tertiary and quarternary carbons (275–300 vs 540–550 ppm/electron) are most probably due to different ΔE values for both types of carbons.     

Carbon-13 NMR spectra of some 4-substituted phenacyl bromides

The ¹³C NMR signals for some 4- substituted phenacyl bromides were assigned. The experimental chemical shifts of the aromatic ring carbons are in close agreement with those calculated using substituent chemical shifts. Both the carbonyl and the α-methylene carbons exhibit upfield shifts compared with those of the corresponding 4-substituted acetophenones.     

Carbon-13 NMR studies of a series of benzylphenols

Carbon-13 NMR spectra of a series of benzylphenols and their O-alkylated derivatives were recorded to find the substituent effects of the benzyl, hydroxybenzyl and alkoxybenzyl groups on the ¹³C chemical shifts. It was found that the methylene bridge carbons show signal shifts mainly due to the mesomeric effects of the OH and OCH₃ substituents, and that in the case of ortho-substituted benzyl compounds, the methylene carbon signals exhibit upfield shifts due to both mesomeric and steric effects.     

NMR- und schwingungsSpektroskopische Untersuchungen höherer Indiumtrialkyle

NMR and Vibrational Spectroscopic Investigations on Higher Indium Trialkyls Several isomeric indium tripentyles and trihexyles are synthesized by known methods. The chemical shifts δ of the ¹³C NMR spectra are used together with those of the corresponding alkanes for determining the increments Δδ(¹³C) = δ(InR₃)–δ(RH). By means of these increments and the Grant/Paul-method the chemical shifts δ(¹³C) of any indium trialkyl can be calculated. The vibrational spectra (IR and Raman) of most liquid trialkyls show very obvious rotameric splittings of the InC vibrations between 450–600 cm^?1. Both frequent conformations of the alkyl ligands with three and more C atoms consist of either a βH atom (notations P_H, S_HH, and T_HHH with vInC between 450–500 cm^?1) or a γC atom (P_C, S_CH, T_CHH with vInC between 550–600 cm^?1) in the transposition to indium. The InC stretching modes of all other more rare configurations can be observed between 500 to 550 cm^?1.     

13C NMR spectra of substituted phenazines: Substituent effects on carbon-13 chemical shifts and the use of 13C?15N coupling constants for the assignment of the aromatic carbons

The ¹³C NMR spectra of 19 substituted phenazines have been measured. Substituent increments of the chemical shifts were calculated for methoxy, carbomethoxy and methyl derivatives. ¹⁵N-Enriched phenazines were synthesized and ⁿJ(¹³C¹⁵N) values were used for the assignment of the signals of the aromatic carbons.