1H and 13C NMR spectral assignment of androstane derivatives

(1)H and (13)C NMR spectroscopic data for 5alpha-androstanes and halo-5alpha-androstanes with different substituents at positions C-3, C-9, C-11 and C-17 were examined and assigned by a combination of 1D and 2D NMR experiments. The substituent effects on the (13)C chemical shifts were compared with those of epi-androsterone, used as a reference compound. The coupling constants (n)J((19)F,(13)C) were measured for compounds 6, 8, 11 and 14.     

Indirect nuclear 57Fe-13C and 57Fe-1H spin-spin coupling in ferrocenes and cyclopentadienyliron complexes: measurements and DFT calculations

Several 57Fe-labeled ferrocene derivatives and other cyclopentadienyliron complexes were studied by 57Fe and 13C NMR with respect to isotope-induced chemical shifts 1Delta12/13C(57Fe) and the magnitude and sign of coupling constants 1J(57Fe,13C) and 2J(57Fe,1H). The geometries of the complexes were optimized by DFT methods [B3LYP/6-311+G(d,p)] and chemical shifts (GIAO) and coupling constants were calculated at the same level of theory. The trends in calculated 57Fe nuclear shielding agree well with the experimental data and, in the case of coupling constants 1J(57Fe,13C) and 2J(57Fe,1H), both sign and magnitude are correctly reproduced.     

Spectral assignments for the aldose reductase inhibitor 4(S)-2,3-dihydro-6-fluoro-2(R)-methylspiro[chroman-4,4'-imidazoline]-2',5'-dione and its synthetic intermediates

The 1H and 13C NMR chemical shifts of the aldose reductase inhibitor 4(S)-2,3-dihydro-6-fluoro-2(R)-methylspiro[chroman-4,4'-imidazoline]-2',5'-dione, methylsorbinil, and its seven synthetic intermediates, have been completely assigned on the basis of DEPT, COSY, g-HSQC and g-HMBC. All C--F coupling constants from one-bond to four-bond in the 13C NMR spectra and H--F and H--H coupling constants from three-bond to four-bond in 1H spectra were obtained.     

Tautomerism of sterically hindered schiff bases. Deuterium isotope effects on 13C chemical shifts

A series of sterically hindered o-hydroxy Schiff bases derived from o-hydroxyaceto- and benzophenones with very short intramolecular hydrogen bonds were described qualitative and quantitatively by deuterium isotope effects on (13)C chemical shift, (n)DeltaC(XD), (n)DeltaF(XD), (1)J(N,H) coupling constants, deltaNCH(3) chemical shifts and UV spectra. All the investigated compounds are found to be tautomeric. The tautomeric character is described by the signs of the deuterium isotope effects on the (13)C chemical shifts. For the 3-nitro-5-chloro derivatives at low temperature, the equilibrium is shifted almost fully toward the proton transferred form in CD(2)Cl(2). Intrinsic deuterium isotope effects on chemical shifts of these compounds as well as (1)J(N,H) coupling constants suggest that a zwitterionic resonance form is dominant for the proton transferred form. Structures, (1)H, (19)F, and (13)C chemical shifts, and deuterium isotope effects on (13)C chemical shifts are calculated by ab initio methods. The potential energy functions and the total deuterium isotope effects are calculated, and they are shown to correspond well with the experimental findings.     

Partially bridge-fluorinated dimethyl bicyclo[1.1.1]pentane-1,3-dicarboxylates: preparation and NMR spectra

Direct fluorination of dimethyl bicyclo[1.1.1]pentane-1,3-dicarboxylate, obtained from [1.1.1]propellane prepared by an improved synthetic procedure, furnished esters of 14 of the 15 possible bridge-fluorinated bicyclo[1.1.1]pentane-1,3-dicarboxylic acids, isolated by preparative GC. Calculated geometries reflect the substitution pattern in a regular fashion compatible with Bent's rules. Considerable additional strain is introduced into the bicyclo[1.1.1]pentane cage by polyfluorination; it is calculated to be as high as 33-35 kcal/mol for hexasubstitution. Three arrangements of the fluorine substituents are especially strain-rich: geminal, proximate, and W-related. The (1)H, (13)C, and (19)F NMR spectra exhibit a striking variety of chemical shifts and long-range coupling constants. These are in good agreement with results calculated with neglect of the bridgehead substituents for all of the chemical shifts by the GIAO-RHF/6-31G//RHF/6-31G and GIAO-RHF/6-31G//MP2/6-31G methods and for many of the coupling constants by the EOM-CCSD/6-311G//MP2/6-311G method. The proximate (4)J(FF) constants are particularly large (50-100 Hz) and show an inverse linear dependence on the calculated F-F distance in the range 2.43-2.58 A.     

Multinuclear magnetic resonance analysis of 2-(trifluoromethyl)-2-oxazoline

(1)H, (19)F, (13)C, (15)N, and (17)O NMR chemical shifts and (1)H-(1)H, (1)H-(19)F, (1)H-(13)C, (19)F-(13)C, and (19)F-(15)N coupling constants are reported for 2-(trifluoromethyl)-2-oxazoline.     

Aromatic C-H...O interactions in a series of bindone analogues. NMR and quantum mechanical study

The aromatic C-H...O hydrogen bonding within the series of the structurally relative indenone derivatives has been studied. The presence of the hydrogen bonds is corroborated by the large low-field chemical shifts of the protons involved in the hydrogen bond observed experimentally and reproduced by quantum mechanical calculations. Further confirmation is provided by analysis of the orbital overlap coefficients, (13)C NMR chemical shifts, and one-bond spin-spin coupling constants J((13)C-(1)H). The relationship between molecular geometry and (1)H NMR chemical shifts of involved protons has a complex nature, but the C-H...O distance is the principal factor.     

1H, 13C and 15N NMR spectral characterization of twenty-seven 1,2-diaryl-(4E)-arylidene-2-imidazolin-5-ones

1H, 13C and 15N NMR chemical shifts and couplings (n)J(H,C) in DMSO-d(6) at 30 degrees C have been determined for 1,2-diaryl-(4E)-arylidene-2-imidazolin-5-one derivatives 1-27. Their chemical shift assignments are based on PFG DQF 1H,1H COSY, PFG 1H,13C HMQC as well as PFG 1H,13C and 1H,15N HMBC experiments. For compounds 1-10 including aryl fluorine substituent(s) also the couplings (n)J(F,C) (n = 1 - 4) are reported.     

1H and 13C NMR chemical shifts and spin-spin coupling constants in trans- and cis-decalins

The NMR parameters characterizing the spectra of trans- and cis-decalins were determined from theoretical calculations and experimental spectra. The calculated values of the shielding constants are in good agreement with the measured chemical shifts, with a small but noticeable difference in accuracy for the bridgehead atoms. Of all the spin-spin coupling constants, only most of (1)J(C,C) and (1)J(C,H) values could be extracted from the spectra, and the corresponding computed values are in good agreement with experiment. It appears that the applied density functional theory (DFT) approach overestimates slightly the J(C,C) coupling and underestimates the differences between one-bond (1)J(C,H) coupling constants. For all these constants [J(C,C), J(C,H) and J(H,H)] through one to three bonds, which could not be obtained experimentally, the predicted values are in good agreement with the general rules relating spin-spin coupling to the number and spatial arrangement of the intervening bonds.     

A multinuclear NMR study of [Pt0(PPh3)2(alkene)] compounds containing asymmetric olefins

The 1H, 13C, 31P, and 195Pt NMR spectra of [Pt0(PPh3)2(eta-ABC(1) = C(2)XY)] compounds (ABC(1)= C(2)XY (1) A = B = X = Y = H; (3) A = B = X = H, Y = CN; (4) A = H, B = p-NO2-Ph, X = COOCH3, Y = CN; (5) A = H, B = Ph, X = COOCH3, Y = CN; (6) A = H, B = Ph, X = Y = CN; (7) A = H, B = OEt, X = Y = CN), where X and Y are electronacceptor substituents, and the 1H spectrum of [Pt0(PPh3)2(eta2-C60)] (2) are reported together with extended analyses and assignments, based also on the ring current effect of the olefin phenyl in (4-6). Deviations from first order in the 13C spectra allowed the determination of the relative signs of the coupling constants J(P(1), C) and J(P(2), C) of the alkene and of the triphenylphosphine carbons. Best fit simulation of the phosphine C ipso spectrum provided also the 13C isotopic shift on phosphorus for (1). These compounds are characterised by strong differences between the two platinum-phosphorus coupling constants in the case of asymmetric olefins (3-7). The chemical shifts of alkene C(1) and C(2) indicate notable polarisation of the olefin after complexation, while the 1J(Pt, C(1)) and 1J(Pt, C(2)) values are in agreement with a stronger interaction of Pt with C(1) than with C(2). These findings together with the trend of 195Pt chemical shifts confirm the important role played by back-donation in the bonding of platinum(0)-olefin compounds.     

NMR study of 5-substituted pyrazolo[3,4-c]pyridine derivatives

Substituted pyrazolopyridines are potent inhibitors of phosphodiesterases and cyclin-dependent kinases. In this study, NMR was used to investigate the potential N1-H and N2-H tautomerism of 5-substituted pyrazolo[3,4-c]pyridine derivatives. Six compounds were fully characterized by using (1)H, (13)C, and (15)N chemical shifts and indirect (1)H--(13)C and (1)H--(15)N coupling constants. The (1)H NMR spectra were measured over a broad range of temperatures. All of the compounds were shown to exist predominantly in the N1-H tautomeric form. Complementary quantum-chemical calculations of the chemical shieldings and indirect spin-spin couplings support the structural conclusions drawn.     

Complex Formation in the Ternary System Tl(III)-CN(-)-Cl(-) in Aqueous Solution. A (205)Tl NMR Study

The existence of mixed complexes of the general formula Tl(CN)(m)()Cl(n)()(3)(-)(m)()(-)(n)() (m + n 相似文献   

NMR analysis of conformationally dependent (n)J(C, H) and (n)J(C, C) in the trisaccharide α-L-Rhap-(1 → 2)[α-L-Rhap-(1 → 3)]-α-L-Rhap-OMe and a site-specifically labeled isotopologue thereof

An array of NMR spectroscopy experiments have been carried out to obtain conformationally dependent (1)H,(13)C- and (13)C,(13)C-spin-spin coupling constants in the trisaccharide α-L-Rhap-(1 → 2)[α-L-Rhap-(1 → 3)]-α-L-Rhap-OMe. The trisaccharide was synthesized with (13)C site-specific labeling at C2' and C2″, i.e. in the rhamnosyl groups in order to alleviate (1)H spectral overlap. This facilitated the measurement of a key trans-glycosidic proton-proton cross-relaxation rate using 1D (1)H,(1)H-T-ROESY experiments as well as a (3)J(C, H) coupling employing 1D (1)H,(13)C-long-range experiments, devoid of potential interference from additional J coupling. By means of both the natural abundance compound and the (13)C-labeled sample 2D (1)H,(13)C-J-HMBC and (1)H,(13)C-HSQC-HECADE NMR experiments, total line-shape analysis of (1)H NMR spectra and 1D (13)C NMR experiments were employed to extract (3)J(C, H) , (2)J(C, H), (3)J(C, C), and (1)J(C, C) coupling constants. The (13)C site-specific labeling facilitates straightforward determination of (n)J(C, C) as the splitting of the (13)C natural abundance resonances. This study resulted in eight conformationally dependent coupling constants for the trisaccharide and illustrates the use of (13)C site-specific labeling as a valuable approach that extends the 1D and 2D NMR methods in current use to attain both hetero- and homonuclear spin-spin coupling constants that subsequently can be utilized for conformational analysis.     

Selective (15)N-labeling and analysis of (13)C-(15)N J couplings as an effective tool for studying the structure and azide-tetrazole equilibrium in a series of tetrazolo[1,5-b][1,2,4]triazines and tetrazolo[1,5-a]pyrimidines

Two general methods for the selective incorporation of an (15)N-label in the azole ring of tetrazolo[1,5-b][1,2,4]triazines and tetrazolo[1,5-a]pyrimidines were developed. The first approach included treatment of azinylhydrazides with (15)N-labeled nitrous acid, and the second approach was based on fusion of the azine ring to [2-(15)N]-5-aminotetrazole. The synthesized compounds were studied by (1)H, (13)C, and (15)N NMR spectroscopy in both DMSO and TFA solution, in which the azide-tetrazole equilibrium is shifted to tetrazole and azide forms, respectively. Incorporation of the (15)N-label led to the appearance of (13)C-(15)N J coupling constants (J(CN)), which can be measured easily using either 1D (13)C spectra with selective (15)N decoupling or with amplitude modulated 1D (13)C spin-echo experiments with selective inversion of the (15)N nuclei. The observed J(CN) patterns permit unambiguous determination of the type of fusion between the azole and azine rings in tetrazolo[1,5-b][1,2,4]triazine derivatives. Joint analysis of J(CN) patterns and (15)N chemical shifts was found to be the most efficient way to study the azido-tetrazole equilibrium.     

19F and 1H NMR spectra of halocarbons

19F NMR chemical shifts and coupling constants are reported for 215 compounds. For 77 of these compounds, 1H NMR spectral data are also given. Long-range couplings, including 8J(F,F) and 5J(F,H), are reported. The complexity of halocarbon spectra owing to the presence of rotational isomers, asymmetric centers, long-range couplings, and chlorine isotope effects are illustrated, and the methods used for analyzing such complex spectra are briefly discussed.     

Reaction of alkyn-1-yl(diorganyl)silanes with 1-boraadamantane: Si-H-B bridges confirmed by the molecular structure in the solid state and in solution

1-Boraadamantane 1 was treated with alkyn-1-ylsilanes 2 containing one or two Si[bond]H functions. Under mild conditions, the reaction gave 4-methylene-3-borahomoadamantane derivatives 4 quantitatively and selectively by 1,1-organoboration. An electron deficient Si-H-B bridge was present in the product. The analogous reaction of 1 with an alkyn-1-yl-disilane 3 gave the corresponding alkene derivative 5, however, without the Si-H-B bridge. Evidence for the Si-H-B bridge in 4 was given by IR data, an extensive set of NMR spectroscopical data ((1)H, (11)B, (13)C, (29)Si NMR) including various unusual isotope effects on chemical shifts and coupling constants, as well as from the molecular structure of one example, 4 e, in the solid state. The precursor of 4 e, alkyne 2 e, Ph(2)Si(H)C[triple bond]CSi(H)Ph(2), was also studied by X-ray analysis.     

1H and 13C NMR spectral characterization of some antimalarial in vitro 2,4‐diamino‐10‐methylpyrimido[4,5‐b]‐5‐quinolone derivatives

We report the ¹H NMR and ¹³C NMR chemical shifts and J(H,H), J(H,F) and J(C,F) coupling constants of 13 2,4‐diamino‐10‐methylpyrimido[4,5‐b]‐5‐quinolone derivatives, some of them with moderate activity against Plasmodium falciparum in vitro. They were characterized and assigned on the basis of ¹H, ¹³C and ¹³C–¹H (short‐ and long‐range) correlated spectra. Copyright © 2002 John Wiley & Sons, Ltd.     

Scalar coupling across [C-H···F-C] interactions in (σ-aryl)-chelating post-metallocenes

The nature and importance of C-H···F-C interactions is a topical yet controversial issue, and the development of spectroscopic methods to probe such contacts is therefore warranted. A series of Group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N-R(1)] ligands bearing a fluorinated R(1) group (CF(3) or F) in the vicinity of the metal has been prepared. The X-ray crystal structure of the CF(3)-substituted Hf derivative features intramolecular C-H···F-C and Hf···F-C contacts. All complexes have been characterized by multinuclear NMR spectroscopy. The (1)H and (13)C NMR spectra of [M(O,C,N-CF(3))(CH(2)Ph)(2)] derivatives display coupling (assigned to (1h)J(HF) and (2h)J(CF) for Ti; (3)J(HF) and (2)J(CF) (through M···F) for Hf and Zr) between the benzyl CH(2) and CF(3) moieties. [(1)H,(19)F]-HMBC NMR experiments have been performed for the M-[O,C,N-R(1)] complexes and their [O,N,C] counterparts, revealing significant scalar coupling across the C-H···F-C interactions for Ti-[O,C,N] and [O,N,C] species.     

Resolution of 13 polycyclic aromatic hydrocarbons by constant-wavelength synchronous spectrofluorometry.

A method capable of determining 13 PAHs (acenaphthene, anthracene, benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, dibenzo[ah]anthracene, fluoranthene, fluorene, indene[1,2,3-cd]pyrene, phenanthrene and pyrene) in a mixture of 16 EPA PAHs by second derivative synchronous spectrofluorometry in the constant wavelength mode was developed. It has not been possible to determine the following PAHs in the mixture: acenaphthylene, benzo[ghi]perylene and naphthalene. The approach studied allows the sensitive, rapid and inexpensive identification and quantitation of 13 PAHs in a solution of hexane. The detection limits are <1 microg L(-1) (except for chrysene and phenanthrene).     

Effect of alkyl group size on the mechanism of acid hydrolyses of benzaldehyde acetals

Hydrolyses of benzaldehyde acetals, PhCH(OR)(2), are specific hydrogen-ion catalyzed when R = methyl, n-butyl, but with secondary and tertiary alkyl derivatives, R = i-propyl, s-butyl, t-butyl, t-amyl, hydrolyses are general-acid catalyzed. The Br?nsted alpha values for both secondary and tertiary alkyl groups are in the range: alpha = 0.57-0.61. A simple iterative procedure was developed to estimate the individual rate constants for general-acid catalysis by the diacid and monoacid forms of succinic acid buffer. Plots of log k(obs) (at [buffer] = 0 M) against pH are linear for the secondary and tertiary acetals, and plots of log k(H) for the H(3)O(+)-catalyzed reaction, (13)C and (1)H chemical shifts, and (1)J(CH) coupling constants against the Charton steric parameter, nu, for alkoxy groups are linear. The second-order rate constant, k(H), increases about 100-fold on going from R = Me to R = t-amyl, indicating the significant role of steric effects on reactivity. Steric effects upon (13)C NMR chemical shifts and coupling constants indicate that increasing the bulk of the alkoxy moiety increases the electron density at the carbon reaction center, which accelerates hydrolysis. Analysis of the Jencks-More-O'Ferrall free energy diagram for the reaction provides support for concerted proton transfer and C-O bond breaking in the transition state for hydrolyses of benzaldehyde acetals with secondary and tertiary alkyl groups in contrast to specific hydrogen catalysis with R = Me and n-Bu. All our results are consistent with rate-determining acid hydrolysis of benzaldehyde dialkyl acetals to hemiacetal intermediates that breakdown rapidly to benzaldehyde.