Automatic assignment of 13C NMR signals based on the Karplus-Pople equation

A modified version of the method of automatic assignment of ¹³C NMR spectra, based on the Karplus-Pople equation is applied to six substituted benzenes. The results are the same as in the case of simple ¹³C chemical shift/charge density linear relationship previously used: -XR substituted aryls (XO, RH, CH₃, CH₂CH₂OH) yield good correlation and correct automatic assignment, while -CH₂CH₂Y substituents (YH, OH, NH₂) yield poor correlation and incorrect assignment.     

Automatic assignment of 13C NMR spectra based on the chemical shift/charge density relationship

An approach for the automatic assignment of ¹³C spectra, based on the chemical shift/charge density relationship, is suggested. All permutations of spectral signals are computer-generated, and for every permutation a least squares adjustment is carried out. The permutation presenting the highest correlation coefficient, or the lowest Hamilton's agreement factor, is considered to be correct. The application is exemplified by the ¹³C chemical shifts of a series of aromatic compounds. It is shown that more reliable assignment is achieved if the considered permutations are restricted by taking intoaccount the signal multiplicity.     

13C NMR spectra of 8-mercaptoquinoline and 8-hydroxyquinoline

The signals in the¹³C NMR spectra of quinoline and its 8-substituted derivatives (SH, SCH₃, OH, OCH₃, NH₂, I, and CH₃), 8,8-diquinolyl disulfide, the 8-hydroxy-N-methylquinolinium ion, and the protonated and anionic forms of 8-hydroxy- and 8-mercaptoquinoline were assigned. The increments of the substituents in the neutral forms of these compounds correlate satisfactorily with those in substituted benzenes and the Swain-Lupton parameters (r = 0.94–0.99). The differences in the ortho increments of the substituents are due to a change in the electron densities on the carbon atoms and also to steric hindrance. The effect of an intramolecular hydrogen bond on the¹³C chemical shift of the quinoline ring of 8-hydroxy- and 8-mercaptoquinoline was examined. The¹³C chemical shifts correlate satisfactorily with the total charges (q) on the carbon atoms in the neutral forms of these compounds. A similar correlation is satisfied to a lesser extent for the protonated and anionic forms because of a change in the bond orders.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 657–662, May, 1980.     

13C chemical shifts of monosubstituted adamantanes

¹³C chemical shifts are reported for adamantane, nine 1-substituted adamantanes and nine 2-substituted adamantanes. The substituents are F, Cl, Br, I, NH₂, OH, CH², CN and CO₂H. The assignments and results are discussed in terms of chemical shift patterns.     

1H and 13C NMR spectra of benzyl compounds

Proton and carbon-13 spectra of benzyl compounds of the general formula (C₆H₅CH₂)_nX with a large variety of X substituents have been measured. While a linear relationship between the CH₂ chemical shift and the substituent electronegativity was found both for ¹H and ¹³C, large deviations from linearity were observed for transition metals such as titanium and zirconium. These later results are correlated with the X-ray studies of the latter compounds.     

13C NMR spectra of substituted thiacyclohexanes

Conclusions The use of the¹J_CH values permits making an unequivocal assignment of the¹³C signals in the spectra of substituted thiacyclohexanes. The steric arrangement of the substituants in 2,4-disubstituted thianes can be established on the basis of the chemical shift values of the C⁶ nuclei. The obtained data can be used to identify the cyclic organosulfur compounds that are isolated from crude petroleum.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 452–454, February, 1982.     

73GE, 17O, 13C NMR Spectra of alkoxygermanes

¹³C, ¹⁷O and ⁷³Ge NMR spectra of seven tetraalkoxygermanes have been investigated. ⁷³Ge resonance signals in these compounds are more sensitive to structure variations than those of ²⁹Si in isostructural alkoxysilanes. ¹⁷O and ¹³C NMR spectra of alkoxygermanes Me_4-n Ge(OR)_n (R = Et, Pr, Bu, i-Bu, s-Bu, CH₂CHCH₂, CH₂CH₂OMe, CH₂CF₃; n = 1–3) have been studied.It has been shown that the magnitude of (p—d)_τ-bonding in the GeO bond is smaller than in the SiO bond, but variation in the extent of (p—d)_τ-overlapping in alkozygermanes with different substituents is similar to that in the isostructural alkoxysilanes.     

The assignment of the 1H and the 13C NMR chemical shifts of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam

The assignment of the signals in the ¹³C and ¹H NMR spectra of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam is difficult for the signal pairs C-2 and C-4, C-1 and C-3, (C-1)? H, (C-2)? CH₃ and (C-4)? CH₃. The ¹³C NMR spectrum recorded under gated decoupling conditions provide long-range couplings which make possible an unambiguous assignment of the ¹³C NMR signal pairs. Application of the ¹H CW off-resonance decoupling technique in recording the ¹³C NMR spectra enables the assignment information from the ¹³C NMR spectrum to be transferred to the ¹H NMR spectrum.     

Saturated amine oxides: part 10. hydroacridines: part 32. linear 17O/13C and 13C/13C chemical shift correlations between saturated azaheterocyclic N‐methylamine N‐oxides,and the methiodides of their parent amines

Two kinds of good linear correlations were found between the chemical shifts of saturated six‐membered azaheterocyclic N‐methylamine N‐oxides and the chemical shifts of the methiodides of their parent amines. One of the correlations occurs between the ¹⁷O chemical shift of the N⁺―O^– oxygen in the N‐oxides and the ¹³C chemical shift of the N⁺―CH₃ methyl group analogously situated in the appropriate methiodide (r = 0.9778). This correlation enables unambiguous configuration assignment of the N⁺―O^– bond, even if the experimentally observed ¹⁷O chemical shift of only one N‐epimer is available, provided the ¹³C chemical shifts of both N⁺―CH₃ groups in the methiodide are known and assigned; furthermore, it can be used also for the estimation of ¹⁷O chemical shifts of the N⁺―O^– oxygens in N‐epimeric pairs of N‐oxides, for which observed ¹⁷O data hardly become available. The second correlation is observed between the ¹³C chemical shift of the N⁺―CH₃ methyl group in the N‐oxides and the ¹³C chemical shift of the N⁺―CH₃ methyl group analogously situated in the appropriate methiodide (r = 0.9785). It can be used for safe configuration assignment of the N⁺―CH₃ group and, indirectly, also of the N⁺―O^– bond in an amine N‐oxide, even if no ¹⁷O NMR data, and the ¹³C chemical shift of only one N‐epimer is available. Copyright © 2015 John Wiley & Sons, Ltd.     

13C NMR spectra of p- and m-substituted phenyl N-methyl- and phenyl N,N-dimethyl-carbamates

¹³C NMR spectra of p- and m-substituted phenyl N-methylcarbamates, phenyl N,N-dimethylcarbamates and p- and m-substituted phenyl propionates were recorded, and their para ¹³C SCS (substituent chemical shifts) were analysed by DSP (dual substituent parameters) and DSP-NLR (non-linear resonance) equations. It was found that the fixed substituent Y, ? OCONHCH₃, ? OCON(CH₃)₂ and ? OCOC₂H₅, were all mild in the sense that DSP analysis gave a good correlation, leaving little room for improvement by the DSP-NLR treatment. Further, the three series of compounds gave similar ρ_I and ρ_R values (para derivatives, 3.2–3.3 and 17.7–18.0; meta derivatives, 5.1–5.2 and 21.8–22.0). Examination of the corresponding analyses of similar compounds indicated that the ρ_I and ρ_R values and, hence, their ratio ρ_R/ρ_R = λ, depended primarily on the nature of the atom through which the fixed substituent Y (e.g. α-C, α-N and α-O) was bonded to the aromatic ring when the Y substituents are mild. The extent of this tendency for compounds with active fixed substituents is also discussed.     

13C13C spin coupling constants in phenanthrene derivatives

The synthesis of six 1-X- (X = OH, OCH₃, OCOCH₃, CH₃, CHO and CN) phenanthrene derivatives with a ¹³C label at C-1 is described. An analysis of the ¹³C¹³C spin coupling constants shows the importance of π-interaction for the coupling constant transmission. Small ¹³C¹³C spin coupling constants over 6 bonds are reported.     

Proximity and the heteroatom effects on the carbon-13 chemical shifts of methyl-substituted phenols,anilines and thiophenols

Upfield substituent-induced ¹³C chemical shifts for aryl carbons of polymethyl substituted benzenes, phenols, anilines and thiophenols were investigated as a function of the proximity between substituents X and CH₃ (X = CH₃, NH₂, OH and SH). The results indicate that the induced shifts of the substituted aryl carbons are, in general, independent of the polar substituent but depend on the number of adjacent substituted aryl carbons. A ?2.0 ppm upfield shift was found for a substituted aryl carbon adjacent to one substituted aryl carbon and a ?3.8 ppm upfield shift for a substituted aryl carbon bound by two substituted aryl carbons. It is suggested that the near additivity of the upfield shifts is the result of changes in the bond order between the aromatic ring carbons in the region of the substituted aryl carbons due to distortion of the ring. The ¹³C chemical shifts of the methyl substituents for methyl substituted phenols, anilines and thiophenols were determined, and it was found that the values could be predicted from the additivity parameters reported for the analogous methylbenzenes plus an additional pair-interaction term associated with the through-space electronic influence of the heteroatom.     

Characterization of organic substrates bound to cross-linked polystyrenes by 13C NMR spectroscopy

The ¹³C NMR spectra of a wide variety of organic substrates bound to 2% cross-linked polystyrenes may be obtained routinely, provided the resins can be sufficiently swollen. The ¹³C chemical shifts of polymer-bound trityl alcohol, polymer-bound monotrityl ethers of the symmertrical diols HO (CH₂)_nOH (n=2, 4, 6, 7, 9 and 10), and some related intermediates in the solid phase synthesis of insect pheromones are presented. ¹³C shift additivity correlations, differing little from those in free trityl ethers, are drawn.     

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.     

Effect of the X and Y substituents on the carbonyl bond in 4-YC<Subscript>6</Subscript>H<Subscript>4</Subscript>C(O)X compounds

Mechanistic aspects of the effect of the X and Y substituents (X = Me, H, CF₃, CN, Br, Cl, F, OH, NH₂; Y = H, NMe₂, NH₂, CN, NO₂) on the carbonyl bond in 4-YC₆H₄C(O)X compounds are discussed on the basis of the ¹³C and ¹⁷O NMR data.     

Magnetic non-equivalence in carbinols of the general formula R1R2C(OH)CH2OR (1H and 13C NMR)

Several compounds of the general formula R¹R²C(OH)CH₂OR containing different geminal group systems have been investigated in proton and carbon magnetic resonances at variable temperatures. The role of steric factors, viz. of the size of substituents and the distances between different parts of the molecules, have been discussed.     

New approach to stereochemical structure determination of bis-selenium-subsituted alkenes

A new approach to determination of the stereochemical structure of bis-selenium-substituted alkenes using experimental ⁷⁷Se NMR studies and B3LYP/6-311G(d) quantum-chemical calculations is developed. Joint analysis of experimental and calculated data allows assignment of signals in the ⁷⁷Se NMR spectrum. The method was evaluated taking the model compounds (PhSe)HC=C(SePh)R (R = COOMe, CH₂NMe₂, CH₂OH, Ph) as examples.     

13C NMR spectra of 1-(N-arylidene)amino-1,2,3-triazoles

The ¹³C nmr spectra of several 1-(N-arylidene)amino-1,2,3-triazoles were determined. The long range influence of substituents on ¹³C resonances of triazole and C = N carbon atoms was examined and a correlation of their chemical shifts with net charge densities (q_{π + σ}) calculated by the CNDO/2 method was made. It was also shown that the dependence of the coupling constants ¹J(CH) for C = N carbon on the substituents is better correlated using electrons in bond values instead of charge densities.     

Proton-coupled 13C NMR spectra of 2- and 3-substituted pyridines

The proton-coupled ¹³C NMR and PMR spectra of pyridine and the 2- and 3-monosubstituted pyridines NC₅H₄X [where X=CH₃, CN, COCH₃, COOCH₃, N(CH₃)₂, NO₂, OCH₃, Cl, or Br] for one-molar solutions of the compounds in DMSO-D₆, have been analyzed. The signs and values of the ¹³C-¹H HSSCs have been determined. Equations have been obtained connecting the ¹³C-¹H SSCCs in the 2- and 3-substituted pyridines and the monosubstituted benzenes. A satisfactory correlation of ¹JCH with the F and R constants of the substituents has been shown.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1223–1230, September, 1984.     

13C NMR Spectra of 8-mercaptoquinoline derivatives

The additivity of the effect of the increments of the substituents on the ¹³C chemical shifts in polysubstituted quinolines is demonstrated. In the case of substitution in the pyridine part of quinoline (R = CH₃, OCH₃, SCH₃) the ortho increments are depressed as compared with the increments in benzene derivatives. This is associated with a change in the charge on the ring carbon atom and polarization of the C-H bond because of steric hindrance.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 937–940, July, 1981.