Substituent effects on carbon-13 NMR chemical shifts of side chain carbonyl carbons of 4-substituted 1-naphthamides

Substituent induced¹³C NMR chemical shifts of side chain carbonyl carbons of several 4-substituted 1-naphthamides have been measured in DMSO-d ₆ solvent. Analysis of the substituent induced chemical shifts by the DSP equation gave the regression equation. Both {ie207-1} and {ie207-2} values were negative. The negative sign on {ie207-3} term indicates the operation of a reverse substituent effect and that π-polarisation is the important mechanism for the transmission of substituent effects by inductive effect. Theperi-hydrogen interaction in naphthamides forces the amide group out of the plane of the naphthalene ring.     

13C and 1H NMR spectral studies of N-alkylmethylquinolinium salts

¹³C and ¹H chemical shifts of fourteen N-alkylmethylquinolinium salts in DMSO-d₆ are reported, and compared with those of the eleven corresponding methylquinoline bases. The influence of ring substitution by methyl groups in the salts and substitution at the nitrogen atom and the effect of the anion are discussed.     

Studies on tacticity of polyacrylonitrile. II. High-resolution nuclear magnetic resonance spectra of 2,4-dicyanopentanes

The NMR spectra of 2,4-DCNP were measured in CCl₄, NaCNS–D₂O, DMSO-d₆, and other solutions. The spectra of the meso form show no significant change with the solvent, but the racemic form shows two kinds of spectra, one of which is observed in a solvent for PAN and the other in a nonsolvent. In the solution, the meso 2,4-DCNP is considered to have two equivalent conformations, TG and G'T, which are the mirror images with each other. The racemic 2,4-DCNP, however, might have predominantly either the TT or GG conformation in CCl₄, pyridine, and benzene, while it has the two conformers with almost equal probability in NaCNS–D₂O and DMSO-d₆. The results obtained from the calculation assuming appropriate constants are in fairly good agreements with the observed spectra of the 2,4-DCNP isomers. The values of chemical shifts and coupling constants used in the calculation correspond to those of PAN which were obtained previously from the analysis of the NMR spectra.     

Hydrogen and carbon NMR data for aminoquinolines and aminoisoquinolines

Hydrogen and carbon chemical shifts and H? H and C? H couplings are reported for six aminoquinolines and six aminoisoquinolines in DMSO-d₆.     

Halide ion effect on the 1H NMR chemical shifts of the residual protons in commonly employed deuterated solvents with tetra-n-butylammonium chloride – Part 2

Many ¹H NMR spectroscopic studies involving supramolecular binding of tetra-n-butylammonium halides (TBAX) with a variety of molecular receptors have been reported to date. Previously we demonstrated that the reference residual proton signal of the deuterochloroform solvent itself in TBAX solutions shifted downfield in a linear TBAX concentration-dependent relationship. We now report that a similar downfield chemical shift behaviour of the residual protons of other commonly employed deuterated solvents with TBACl can be seen for dichloromethane-d₂ and acetonitrile-d₃, but in acetone-d₆, methanol-d₄ and DMSO-d₆, upfield shifts are observed. A hypothesis based on Density Functional Theory (DFT) modelling is presented to account for this behaviour.     

NMR studies on aromatic compounds: VI—13C NMR spectra of some mono- and disulphonato-substituted hydroxynaphthoic acids in DMSO-d6–water solution

Carbon-13 NMR spectra of sulphonatosubstituted hydroxynaphthoic acids were recorded with and without proton noise decoupling in DMSO-d₆–water (2:1 v/v). The ¹³C chemical shifts were assigned by using substituted naphthalenes as reference compounds. The additivity law of the substituent effects is discussed for the naphthalenesulphonic acids studied.     

Carbon-13 chemical shift assignments of the nitration products of pyrene

¹³C and ¹H nuclear magnetic resonance (NMR) spectra have been obtained in order to identify the six nitration products of pyrene—1-nitropyrene, 1,3-dinitropyrene, 1,6-dinitropyrene, 1,8-dinitropyrene, 1,3,6-trinitropyrene and 1,3,6,8-tetranitropyrene. ¹³C chemical shifts in DMSO-d₆ were assigned using empirical rules, with particular emphasis on the additivity of the substituent effects. Carbon spectra of separated dinitromixtures enabled identification of the previously unreported 1,3-isomer, and proton spectra differentiated the 1,6- and 1,8- isomers.     

NMR studies in the heterocyclic series XXIV—1H, 13C and 15N study of 15N labelled indazoles

The ¹⁵N chemical shifts and ¹H? ¹⁵N and ¹³C? ¹⁵N coupling constants of nine monolabelled indazoles were measured and assigned. The experimental values are discussed in terms of the indazolic and iso-indazolic structures, and compared with literature data for other related heterocycles. All the results are consistent with an N-1(H) tautomeric structure for indazole in DMSO-d₆.     

Etudes d'Hétérocycles Pentagonaux Polyhétéroatomiques par RMN du 13C. Effets de Substituant,de la Benzocondensation et Etude de la Tautomèrie Prototropique en Série Benzothiazolique

The ¹³C NMR spectra of 43 benzothiazoles have been recorded in DMSO-d₆. All carbon atoms have been attributed in an unambigous way owing to substituent effects in position 4, 5, 6 or 7. We discuss variations of chemical shifts as a function of the nature of the substituent in position 2 (equation of type: Δδ = aF+bR+cQ+d′), annelation in the benzoheterocyclic series, and prototropic tautomerism in the benzothiazolic series (in the case of the substituent in the 2-position being an OH, SH or NHR group).     

1H and 13C NMR study of 8-hydroxyquinoline and some of its 5-substituted analogues

¹H and ¹³C NMR spectra of 8-hydroxyquinoline (oxine) and its 5-Me, 5-F, 5-Cl, 5-Br and 5-NO₂ derivatives have been studied in DMSO-d₆ solution. The ¹H and ¹³C chemical shifts and proton–proton, proton–fluorine, carbon–proton and carbon–fluorine coupling constants have been determined. The ¹H and ¹³C chemical shifts have been correlated with the charge densities on the hydrogen and carbon atoms calculated by the CNDO/2 method. The correlation of the ¹H and ¹³C chemical shifts with the total charge densities on the carbon atoms is approximately linear (r_H² = 0.85, r_C² = 0.84). The proton in peri position to the nitro group in 5-NO₂-oxine is an exception.     

1H NMR study of cyclo-L-Thr-L-Thr and cyclo-L-Thr-L-His conformations

Cyclodipeptides containing L -Thr and L -His residues have been studied by ¹H NMR in D₂O and DMSO-d₆. In the neutral form in D₂O as in DMSO-d₆, the folded form of the L -His residue is not unique. The diketopiperazine ring seems to be not strictly planar.     

15N-, 1H-, and 13C-NMR chemical shifts and electronic properties of aromatic diamines and dianhydrides

We measured the ¹⁵N-, ¹H-, and ¹³C-NMR chemical shifts for a series of aromatic diamines and aromatic tetracarboxylic dianhydrides dissolved in DMSO-d₆, and discuss the relationships between these chemical shifts and the rate constants of acylation (k) as well as such electronic-property-related parameters such as ionization potential (IP), electronic affinity (EA), and the energy ε of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The ¹⁵N chemical shifts of the amino group of diamines (δ_N) depend monotonically on the logarithm of k (log k) and on IP. We inferred the reactivities of diamines whose acylation rates have not been measured from their δ_N, and we propose an arrangement of diamines in the order of their reactivity. The ¹H chemical shift of amino hydrogens (δ_H) and the ¹³C chemical shift of carbons bonded to nitrogen (δ_C) are roughly proportional to δ_N, but these shifts are not as closely correlated with log k and IP. Although the ¹³C chemical shifts of the carbonyl carbon of dianhydrides (δ_C,) varies much less than the δ_C and δ_N of diamines, δ_C, can be an index of acylation reactivity for dianhydrides because it is closely correlated with ε_LUMO. These facts indicate that the chemical shifts of diamines and dianhydrides are displaced according to their electron-donor and electron-acceptor properties, and that these chemical shifts can be used as indices of the electronic properties of monomers. Changes in reactivity caused by the introduction of trifluoromethyl groups into diamines and dianhydrides are inferred from the displacements of δ_N and δ_C © 1992 John Wiley & Sons, Inc.     

H and C NMR spectroscopy of 9-acridinones

The ¹H and ¹³C NMR spectra of 9-acridinone and its five derivatives dissolved in CDCl₃, CD₃CN and DMSO-d₆ were measured in order to reveal the influence of the constitution of the compounds and features of the solvents on chemical shifts and ¹H-¹H coupling constants. Experimental data were compared with theoretically predicted chemical shifts, on the GIAO/DFT level of theory, for DFT (B3LYP)/6-31G^∗∗ optimized geometries of molecules—also for four other 9-acridinones. This comparison helped to ascribe resonance signals in the spectra to relevant atoms and enabled revelation of relations between chemical shifts and physicochemical features of the compounds. It was found that experimentally or theoretically determined ¹H and ¹³C chemical shifts of selected atoms correlate with theoretically predicted values of dipole moments of the molecules, as well as bond lengths, atomic partial charges and energies of HOMO.     

Carbon-13 NMR studies on some 5-substituted quinoxalines

Eleven 5-substituted quinoxalines (NO₂, NH₂, COOH, OCH₃, CH₃, OH, F, Cl, Br, I, CN, the latter five not reported previously) have been synthesized by standard methods. Their ¹³C NMR spectra have been measured in DMSO-d₆ and assigned on the basis of substituent parameters, by line widths and by intensities. The chemical shifts compare favorably with those calculated using benzene substituent parameters, and are very close to those of corresponding carbons in 1-substituted phenazines. The correlation with the chemical shifts of the corresponding positions in 1-substituted naphthalenes is also close except for those of carbons 4a and 8a in the quinoxalines which, due to their proximity to nitrogen, are downfield (in some cases 12 ppm) of the signals of the corresponding carbons in naphthalene. 5-Fluoroquinoxaline was also measured in CDCl₃, CD₃COCD₃, CD₃CN, CD₃OD, C₆D₆ and CD₃COOD. In all solvents an abnormally low ²J(CF) (～ 12 Hz) was found for C-4a and no C? F spin-spin splitting could be detected for the three-bond coupling of C-8a. Similar abnormalities were found in 2-fluoroaniline and 2-fluoroacetanilide. There are linear relationships between the Q parameter of the substituent and the chemical shift of carbons 4a, 5 and 6. A linear relationship also exists between the chemical shift of C-8 (‘para’ position) and the Hammett σ_p parameter of the substituent.     

Synthesis of Mono- and Disaccharide 4-[(ω-Sulfanylalkyl)oxy]benzoylhydrazones as Potential Glycoligands for Noble Metal Nanoparticles

A procedure has been developed for the synthesis of previously unknown aldose 4-[(ω-sulfanylalkyl) oxy]benzoylhydrazones (where alkyl is hexyl or decyl and aldoses are D-glucose, D-galactose, D-maltose, and D-lactose) that a repromising glycoligands for noble metal nanoparticles. According to the ¹H and ¹³C NMR data, 4-[(ω-sulfanylalkyl)oxy]benzoylhydrazones derived from D-glucose, D-maltose, and D-lactose in crystal and in DMSO-d₆ solution have exclusively the cyclic pyranose structure (α- and β-anomers). D-Galactose 4-[(ω-sulfanylalkyl)oxy]benzoylhydrazones in DMSO-d₆ solution exist as tautomeric mixtures of cyclic pyranose and open-chain acylhydrazone structures.

     

Structure of aldose condensation products with 2-hydroxyand 2-sulfanylbenzohydrazides

The structure of the condensation products of 2-hydroxy- and 2-sulfanylbenzohydrazides with a series of aldoses (L-arabinose, D-ribose, L-ramnose, D-galactose, D-glucose, D-mannose) was studied by ¹H and ¹³C NMR spectroscopy. The condensation products of monosaccharides with 2-hydroxybenzohydrazide in DMSO-d ₆ solution exist as equilibrium mixtures of linear hydrazone and cyclic pyranose and furanose forms, the cyclic tautomers being represented by two stereoisomers (α- and β-anomers). The aldose condensation products with 2-sulfanylbenzohydrazide in the crystalline state have cyclic 1,3,4-benzothiadiazepine structure, while in DMSO-d ₆ solution they undergo complete or partial isomerization into cyclic pyranose tautomer.     

Correlation of substituted aromatic β‐diketones' characteristic protons chemical shifts with Hammett substituent constants

Influence of dibenzoylmethane's substituents in meta and para positions on chemical shift values of tautomers' characteristic protons was investigated in four solvents with ¹H NMR spectroscopy: acetone‐d₆, benzene‐d₆, CDCl₃ and deuterated dimethyl sulfoxide (DMSO‐d₆). It was proved that the influence of substituents on chemical shifts strongly depends on the kind of the solvent; the greatest changes were observed in benzene‐d₆ and the smallest in CDCl₃. In acetone‐d₆ and DMSO‐d₆, the influence of substituents on chemical shifts is similar and the most regular. It allowed a fair correlation of chemical shifts of para‐substituted dibenzoylmethane derivatives' characteristic protons with Hammett substituent constants in these solvents. In CDCl₃, characteristic protons' chemical shifts were near ¹H NMR spectroscopy measurement error limits, and, therefore, correlation with Hammett substituent constants in this solvent was unsatisfactory. In benzene, although the changes of chemical shifts are the most evident, the changes are also the most irregular, and, therefore, correlation in this solvent failed completely. Results of meta‐substituted derivatives were much more irregular, and their correlation with Hammett substituent constants was poor in all investigated solvents. Copyright © 2013 John Wiley & Sons, Ltd.     

Stabilisation of alkylcarbamate anions using neutral hydrogen bond donors

The interactions of a series of urea-based anion receptors and alkylcarbamate species formed by the reaction of carbon dioxide with primary amines have been investigated by ¹H NMR. Significant downfield shifts in the NH proton signals of the receptors in the presence of the alkylcarbamates were observed, consistent with classical host:anion hydrogen-bonding. This observation demonstrates that neutral hydrogen bond donor receptors can compete with ammonium cations to bind carbamates in DMSO-d₆ solution.     

1H, 13C, 15N NMR and IR Spectroscopic Studies of a Rh(II) Complex of Thiourea

A rhodium(II) complex of thiourea (Tu), Rh₂(OAc)₄Tu₂, has been prepared from Rh₂(OAc)₄(H₂O)₂ and characterized. A shift of the ν(N?H) vibration towards higher frequencies in the IR spectrum is consistent with sulfur coordination to rhodium(II). ¹³C NMR spectra recorded in DMSO-d ₆ reveal that thiourea is replaced by DMSO-d ₆ solvent, followed by replacement of acetate ions by free thiourea. ¹⁵N NMR indicates some nitrogen involvement in coordination to form an S?N chelate.     

Investigating the effects of structure on sulfate recognition by neutral dipeptide receptors

A small library of neutral peptide-based anion receptors was synthesised, where changes were made to the scaffold structure to investigate the effect these structural features have on the anion binding ability of these receptors. These changes included shortening the peptide side chain lengths, increasing the number of electron withdrawing substituents present on the squaramide phenyl substituents and increasing the length and flexibility of the peptide backbone. An effort was also made to increase the aqueous solubility of these receptors by functionalising the N-terminus of the peptide with a hydrophilic moiety. All the receptors displayed strong affinity and selectivity for sulfate in 20% v/v H₂O/DMSO-d₆ and a 5-fold increase in the affinity of the thiourea receptors was observed upon shortening the side chains by one methylene unit. Overall, the squaramide derivatives displayed much stronger association, in this competitive media, than the thiourea based receptors.