Analysis of F and C NMR spectra of tetrafluorophthalic anhydride and its derivatives

¹⁹F and ¹³C NMR spectra of perfluorinated compounds (i.e., tetrafluorophthalic anhydride, its hydroxyl- and amino-derivatives, N-pentafluorophenyltetrafluorophthalimide, and hexafluoroindan-1,3-dione) were analysed. Different signals in NMR spectra were assigned based on the analysis of spin-spin coupling constants. All assignments made were further confirmed by density functional theory (DFT) calculations of ¹³C chemical shifts and J_C,F coupling constants.     

Configuration of functional trifluoromethylated dienoates,aryldienoates and trienoates

The configuration of certain trifluoromethylated functional dienoates, aryldienoates and trienoates is presented by the measurement of their ¹³C NMR and ¹⁹F NMR chemical shifts, and their ³ J(C–F), ⁴J(H–F) and through‐space ⁵J(H–F) coupling constants. Copyright © 2002 John Wiley & Sons, Ltd.     

Investigation of two‐ and three‐bond carbon–hydrogen coupling constants in cinnamic acid based compounds

Two‐ and three‐bond coupling constants (²J_HC and ³J_HC) were determined for a series of 12 substituted cinnamic acids using a selective 2D inphase/antiphase (IPAP)‐single quantum multiple bond correlation (HSQMBC) and 1D proton coupled ¹³C NMR experiments. The coupling constants from two methods were compared and found to give very similar values. The results showed coupling constant values ranging from 1.7 to 9.7 Hz and 1.0 to 9.6 Hz for the IPAP‐HSQMBC and the direct ¹³C NMR experiments, respectively. The experimental values of the coupling constants were compared with discrete density functional theory (DFT) calculated values and were found to be in good agreement for the ³J_HC. However, the DFT method under estimated the ²J_HC coupling constants. Knowing the limitations of the measurement and calculation of these multibond coupling constants will add confidence to the assignment of conformation or stereochemical aspects of complex molecules like natural products. Copyright © 2016 John Wiley & Sons, Ltd.     

Conformational analysis of 2-OAryl-2-oxo-4,6-dimethyl- and -4-methyl-1,3,2λ5-dioxaphosphorinanes. Spectroscopic,X-Ray,and solid-state 13C and 31P studies

Results of IR and ¹H, ¹³C, and ³¹P NMR studies of the anancomeric title compounds ( 2–5 ) and compound 1 (Scheme 1) are analyzed to search for the existence of high-energy boat or twist-boat conformations in the equatorial epimers. While the difference in frequencies (Δν)_P=O between the axial and equatorial compounds and ¹³C NMR J_POCC and anti J_POCCH3 values suggest the participation of twist-boat conformations for the equatorial isomers, coupling constants in ¹H NMR J_H4H5a or J_H6H5a and J_H4H5e or J_H6H5e of the equatorial isomers 2e–4e along with the lack of a large ³J_PH in ³¹P NMR are consistent with predominant chair conformations. In addition, an X-ray structure of the equatorial 2-p-nitrophenoxy-2-oxo-cis-4,6-dimethyl-1,3,2-dioxaphosphorinane ( 4e ) showed that the molecule adopts a chair conformation with no severe ring flattening in the OPO region in the solid state. X-ray structures of trans- 4 and trans- 5 displayed chair conformations with mild ring flattening especially in the axial methyl region, presumably as a result of the steric methyl-oxygen interaction. CPMAS ¹³C and ³¹P NMR spectra of 4a and 4e provide evidence against the presence of a significant contribution of a twist-boat conformation in solid equatorial 4e . The NMR spectral analysis of 1e , on the other hand, suggests a substantial contribution of a twist conformation as well as, possibly, some contribution of the inverted chair. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 509–516, 1997     

The small‐scale preparation and NMR characterization of isotopically enriched organotin compounds

Synthetic methods for the small‐scale laboratory preparation of isotopically enriched dibutyltin dichloride, dibutyltin di‐iodide, tributyltin chloride, tributyltin iodide, diphenyltin dichloride, triphenyltin chloride and triphenyltin iodide have been successfully established. Organotin iodides were prepared from redistribution reactions between tin(IV) iodide and the corresponding tetraorganotin, with the exception of dibutyltin di‐iodide, which was prepared directly from the reaction between tin metal and iodobutane. The development of novel procedures for the dealkylation/dearylation of tetraorganotins by acid hydrolysis produced superior yields of tributyltin chloride and diphenyltin dichloride in comparison with redistribution reactions. Organotin iodide redistribution reaction products were converted to their chloride analogues via the fluoride salts using an aqueous ethanolic solution of potassium fluoride. The insolubility of organotin fluoride salts was exploited to isolate and purify the isotopically enriched compounds, and to prevent losses during the purification procedure. The nuclear magnetic resonance (NMR) spectroscopic study of ‘natural abundance’ and isotopically enriched organotin compounds gave proton (¹H) and carbon‐13 (¹³C) spectra for butyltins, Bu_4−nSnX_n, and phenyltins, Ph_4−nSnX_n (X = I, Cl), allowing the assignment of ­¹H and ¹³C chemical shifts, and ¹¹⁹Sn–¹³C and ¹¹⁷Sn–¹³C coupling constants. The ¹³C NMR spectroscopic analysis of ¹¹⁷Sn‐enriched organotin compounds has allowed the assignment of certain resonances and tin–carbon coupling constants which were previously unobservable. The spectral patterns show that Δ(¹H) and Δ(¹³C) values are sensitive to structural changes, and that ¹³C shielding decreases with an increase in the electronegativity of the substituent. The tin–carbon coupling constants are also sensitive to structural changes, and for alkyl and aryl compounds the couplings decrease in the order ¹J > ³J > ²J > ⁴J. The ¹³C chemical shift values and the magnitude of tin–carbon coupling constants are shown to be solvent‐dependent. The ¹³C spectra of the isotopically enriched compounds show that the degree of isotopic enrichment and the nature of the isotope used (magnetic or non‐magnetic) are reflected in the spectral pattern obtained. Copyright © 2000 John Wiley & Sons, Ltd.     

Characterization of tri-o-methylcellulose by one- and two-dimensional NMR methods

Tri-O-methylcellulose was prepared from partially O-methylated cellulose and its chemical shifts (¹H and ¹³C), and proton coupling constants were assigned using the following NMR methods: (1) One-dimensional ¹H and ¹³C spectra of the title compound were used to assign functional groups and to compare with literature data; (2) double quantum filtered proton–proton correlation spectroscopy (¹H, ¹H DQF-COSY) was used to assign the chemical shifts of the network of 7 protons in the anhydroglucose portion of the repeat unit; (3) the heteronuclear single-quantum coherence (HSQC) spectrum was used to establish connectivities between the bonded protons and carbons; (4) the heteronuclear multiple-bond correlation (HMBC) spectrum was used to connect the hydrogens of the methyl ethers to their respective sugar carbons; (5) the combination of HSQC and HMBC spectra was used to assign the ¹³C shifts of the methyl ethers; (6) all spectra were used in combination to verify the assigned chemical shifts; (7) first-order proton coupling constants data (J_H,H in Hz) were obtained from the resolution-enhanced proton spectra. The NMR spectra of tri-O-methylcellulose and other cellulose ethers do not resemble the spectra of similarly substituted cellobioses. Although the ¹H and ¹³C shifts and coupling constants of 2,3,6-tri-O-methylcellulose closely resemble those of methyl tetra-O-methyl-β-D -glucoside, there are differences with regard to the chemical shifts and the order of appearances of the resonating nuclei of the methyl ether appendages and the proton at position 4 in the pyranose ring. H4 in tri-O-methylcellulose is deshielded by the acetal system comprising the β-1→4 linkage, and it resonates downfield. H4 in the permethylated glucoside is not as deshielded by the equitorial O-methyl group at C4, and it resonates upfield. The order of appearance of the ¹H and ¹³C resonances in the spectra of the tri-O-methylcellulose repeat unit (from upfield to downfield) are H2 < H3 < H5 < H6a < H3a < H2a < pro R H6B < H4 < pro S H6A ≪ H1 and C6a < C3a < C2a < C6 < C5 < C4 < C2 < C3 ≪ C1, respectively. Close examination of the pyranose ring coupling constants of the repeat unit in tri-O-methylcellulose supports the ⁴C₁ arrangement of the glucopyranose ring. Examination of the proton coupling constants about the C5-C6 bond (J_5,6A and J_5,6B) in the nuclear Overhauser effect difference spectra revealed that the C6 O-methyl group is predominantly in the gauche gauche conformation about the C5-C6 bond for the polymer in solution. © 1999 John Wiley & Sons, Inc.* J Polym Sci A: Polym Chem 37: 4019–4032, 1999     

Chemo-and stereoselectivity of the reaction of aromatic aldehydes with triphenylphosphine and trichloroacetic acid derivatives

Aromatic aldehydes react with triphenylphosphine and ethyl trichloroacetate or trichloroacetonitrile to give the corresponding benzylidene dichlorides or α-chlorocinnamic acid derivatives. The chemo-and regioselectivity of these reactions depend on both the substituent in the aromatic ring and reaction conditions. The product configuration was determined on the basis of the coupling constants ² J _CH and ³ J _CH in the ¹³C NMR spectra.     

Substituent effects on nuclear spin–spin carbon–carbon coupling constants in derivatives of acetylene

¹J(¹³C?¹³C) nuclear spin–spin coupling constants in derivatives of acetylene have been measured from natural abundance ¹³C NMR spectra and in one case (triethylsilyllithiumacetylene) from the ¹³C NMR spectrum of a ¹³C-enriched sample. It has been found that the magnitude of J(C?C) depends on the electronegativity of the substituents at the triple bond. The equation ¹J(¹³C?¹³C) = 43.38 E_x + 17.33 has been derived for one particular series of the compounds Alk₃SiC?CX, where X denotes Li, R₃Sn, R₃Si, R₃C, I, Br or Cl. The ¹J(C?C) values found in this work cover a range from 56.8 Hz (in Et₃SiC?Li) to 216.0 Hz (in PhC?CCI). However, the ¹J(C?C) vs E_x equation combined with the Egli–von Philipsborn relationship allows the calculation of the coupling constants in Li₂C₂ (32 Hz) and in F₂C₂ (356 Hz). These are probably the lowest and the highest values, respectively, which can be attained for ¹J(CC) across a triple bond. The unusually large changes of the ¹J(C?C) values are explained in terms of substituent effects followed by a re-hybridization of the carbons involved in the triple bond. INDO FPT calculations performed for two series of acetylene derivatives, with substituents varied along the first row of the Periodic Table, corroborate the conclusions drawn from the experimental data.     

Group IV organometal derivatives of pyridine. I—A 1H and 13C NMR investigation of trialkylmetal derivatives of pyridine

The proton and carbon-13 NMR spectra of thirteen trialkylmetal derivatives of pyridine, several of which were previously unknown, have been recorded and analysed. The proton NMR spectra show variations in proton chemical shifts but not in proton-proton coupling constants when the metal substituent is changed; the ring proton-metal coupling constants ⁿJ(M? H) in the tin and lead derivatives correspond closely with the corresponding proton-proton couplings ⁿJ(H? H) in pyridine. The carbon-13 chemical shifts of the carbons bound to the metal can apparently be correlated with the electron-donating ability of the trialkylmetal group. In the trimethylstannylpyridines the value of ¹J(Sn? C_ring) varies greatly with the position of the Me₃Sn group.     

Carbon-13, 1H coupling constants for benzene and the tropylium ion

The ¹³C, ¹H spin–spin coupling constants for benzene and tropylium fluoroborate have been measured from the ¹³C NMR spectra of [D₅]benzene and the [D₆]tropylium ion using a new experimental technique which employs highly deuterated compounds and ²D-decoupling. For benzene the new data are in good agreement with earlier results. For the tropylium ion we find ¹J = 166.79, ²J ? 0, ³J = 9.99 and ⁴J = (?)0.64 Hz. Secondary isotope effects for ¹³C chemical shifts, including one over four bonds, are reported.     

Carbon-13 nuclear magnetic resonance studies of creatine,creatinine and some of their analogs

Creatine (N-methyl-N-amidinoglycine), creatinine (1-methyl-2-aminoimidazolin-4-one) and a series of 38 of their close structural analogs have been examined using natural abundance ¹³C NMR spectroscopy at 25.16 MHz. Both proton-coupled and proton noise-decoupled spectra were recorded. Unequivocal assignments of the carbon resonances could be made in the vast majority of cases. Both ¹³C NMR chemical shifts and ¹J(CH) values can be used to characterize and to differentiate readily between analogs of creatine and analogs of creatinine. For example, the ¹J(CH) coupling constants for the α-carbons of the acyclic creatine analogs were all in the 140–142 Hz range, whereas the corresponding coupling constants for the related, cyclized creatinine analogs were all in the 150–152 Hz range.     

1H-, 13C-UND 31P-NMR-SPEKTROSKOPISCHE UNTERSUCHUNGEN AN BIS-(DIALKOXYTHIOPHOSPHORYL)-UND-(DIALKOXYPHOSPHORYL)-SULFANEN UND-POLYSULFANEN

Abstract

Compounds of the following structure

(R¹O)₂(X)P[sbnd]Y–P(X)(OR²)₂

(X = O, Y = S_n (n = 1–4), R¹ = R² = Me, iPr;

X = S, Y = S_n (n = 1–4), R¹, R² = Me, Et, iPr, iBu;

X = S, Y = S-Se-S, S-Te-S, R¹ = R² = Me

were prepared and their NMR spectra were analysed. Depending on the number of sulfur atoms, bonded between the phosphorus atoms, typical ranges of the P-P coupling constants were found for the different sulfanes investigated: ²J_PP from-10 to-20 Hz, ³J_PP less than 3 Hz, ⁴J_PP from +10 to +13 Hz and ⁵J_PP less than 1 Hz. For the small vicinal coupling constants and the relatively large values of ⁴J_PP different possibilities of their interpretation are given.     

Unusual deuterium isotope effects in 13C NMR spectra of trans-stilbene

A detailed analysis of the ¹³C NMR spectra of trans-stilbene and ten deuteriated trans-stilbenes has been undertaken. Some unusual deuterium isotope effects on carbon–hydrogen spin–spin coupling constants could not be explained by the ordinary primary and secondary isotope effects. The positive and negative changes of ⁿJ(CH) were interpreted in terms of a steric effect, the vibrational influence of the C? D bond and the para-effect induced by deuterium. In this respect, deuterium behaves as a real substituent with electronic properties different from those of hydrogen. The deuterium isotope effects on ¹³C NMR chemical shifts and carbon–deuterium coupling constants have also been determined.     

Carbon-13 NMR studies of monohydroxylated and monochlorinated derivatives of Z- and E-p-menthanes

J(¹³C¹H) coupling constants for some methyl- and aminopyrimidines have been determined by ¹³C NMR. Both the one-bond and long-bond and long-range coupling constants follow general trends which can be summarized in a few simple rules. In particular, the ³J(C-i,H) coupling constants between a ring carbon C-i and the ring protons are larger than the ²J(C-i,H) coupling constants. The opposite is observed for the couplings between the ring carbons and the methyl protons: ³J(C,Me). These general rules are very useful for the assignment of resonances in complex ¹³C spectra of pyrimidines and seem to be valid for other 6-membered aromatic nitrogen heterocycles. Furthermore, the additivity of substituent effects on ¹J (CH) for monosubstituted pyrimidines allows the estimation of ¹J (CH) for polysubstituted pyrimidines with a very good accuracy.     

The first naphthodiazaphosphorinane in the solid phase; syntheses, spectroscopic studies and X-ray crystallography of some new 1,3,2-diheterophosphorus compounds

New heterocyclic compounds of diazaphosphorinanes, diazaphospholes, and oxazaphospholes were synthesized and characterized by ¹H, ¹³C, ³¹P, NMR, IR spectroscopy, and CHN elemental analysis. The 3D structure of compound (5) was determined by X-ray crystallography. Since benzo- or naphthodiazaphospholes/diazaphosphorinanes containing aromatic rings are usually unstable in the solution state, their single crystal structures are rarely reported and, to the best of our knowledge, this structure is the first occasion of naphthodiazaphosphorinanes obtained here. It is noticeable that the P=O and C=O bonds are closer to syn than anti configuration and the P=O bond is placed in a pseudo-equatorial position. This structure produced a 3D polymeric chain via strong hydrogen bonds and electrostatic short contacts. Due to the ring strain of five-membered rings, for all diazaphospholes great ² J(PNH_endocyclic) coupling constants (about 18.0 Hz), as well as high ^2,3 J(P,C) coupling constants for the aromatic carbon atoms connected to the five-membered ring (about 14.5, 13.5 Hz, respectively) were measured. Replacement of one NH group in a diazaphosphole ring by an oxygen atom caused exceedingly decreased ring strain and hence highly diminished ² J(PNH_endocyclic) coupling constant. Furthermore, ³¹P NMR spectra of oxazaphospholes, like the spectra of diazaphosphorinanes, indicated highly shielded phosphorus atoms relative to those of their diazaphospholes analogs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Facile structural elucidation of imidazoles and oxazoles based on NMR spectroscopy and quantum mechanical calculations

The reaction of 1,2,3-tricarbonyl derivatives with hexamethylenetetramine and ammonium acetate in acetic acid provides an unambiguous approach to the synthesis of imidazoles, whereas the Bredereck reaction of α-haloketones in formamide, yields both imidazoles and oxazoles. Herein we describe a facile methodology for distinguishing between these heterocyclic compounds based on a combination of NMR spectroscopy and quantum mechanical calculations. In the NMR data the oxazole C-2 has a chemical shift of ca. 150 ppm whereas in the imidazoles it is found at ca. 135 ppm, with a ¹J_C-H of ca. 250 Hz for the oxazoles and ca. 210 Hz for the imidazoles. ¹J_C-H values can be easily obtained from a gated-decoupled ¹³C spectrum, and even more trivially, from the separation of the H-2 ¹³C satellites in the ¹H spectra. Additionally, the computed NMR data, obtained from density functional theory, are found to be in good agreement with the experimental data and serve as valuable tools in identifying the products of the Bredereck reaction.     

Long-Range 31P-31P Spin Coupling Constants in the 31P NMR Spectra of Phosphite Triesters

Abstract

Data are presented on the magnitudes of ⁵ J _pp and ⁶ J _PP spin-spin coupling constants in the ³¹P NMR spectra of a variety of novel polyphosphite triesters.     

Conformation of δ-cadinol in solution

An assignment of the signals in the¹³C and¹H NMR spectra of the natural sesquiterpene alcohol δ-cadinol has been made by the NMR method (INADEQUATE, 2D-INADEQUATE, two-dimensional C-H correlation on¹J_CH constants, two-dimensional homonuclear J-spectroscopy) and the spin-spin coupling constants¹J_CC and some J_HH constants have been determined. By comparing the experimental and calculated values of the spin-spin coupling constants J_HH it has been shown that the predominant conformation of the δ-cadinol molecule in solution is that in which ring A has the half-chair form and ring B the chair form with an equatorial arrangement of the hydroxy and isopropyl groups. Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 635–638, September–October, 1990.     

Stereochemicai study of 7-aryl-1,7,8,8a-tetrahydro-3(2H)indolizinones by1H and13C NMR

Stereochemistry of 7-aryl-1,7,8,8a-tetrahydro-3(2H)-indolizinones was studied by¹H and¹³C NMR. Complete assignment of¹H NMR signals and analysis of¹H-¹H coupling constants were performed using the iterative PANIC program. Values of³ J _6,7,³ J _7,8endo, and⁴ J _5,7 allow one to unambiguously identify the correspondingexo- andendo-stereoisomers. For stereoisomers with exo-orientation of H(7), complete assignment of¹³C NMR signals was performed on the basis of analysis of the¹³C-¹H coupling constants using two dimensional heteronuclear shift-correlating spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 591–593, March, 1996.     

Temperature dependences of J(C,H) and J(C,D) in 13CH4 and some of its deuterated isotopomers

The nuclear spin—spin coupling constants J(C,H) and J(C,D) have been measured over the temperature range 200–370 K for the methane isotopomers ¹³CH₄, ¹³CH₃D, ¹³CHD₃ and ¹³CD₄. The coupling constants increase with increasing temperature for any one isotopomer and decrease with increasing secondary deuterium substitution at any one temperature. The results are entirely attributable to intramolecular effects and the data have been fitted by a weighted least-squares regression analysis to a spin—spin coupling surface thereby yielding a value for ¹J_e(C,H), the coupling constant at equilibrium geometry, and values for the bond length derivatives of the coupling. We find that ¹J_e(C,H) = 120.78 (±0.05) Hz which is about 4.5 Hz smaller than the observed value in ¹³CH₄ gas at room temperature. Results are also reported for J(H,D) in ¹³CH₃D and ¹³CHD₃ for which no temperature dependence was detected.