bluuebunny/crossref_metadata_2025 huggingface dataset:
Triterpenoids. Part II—Carbon‐13 NMR spectra of 18β‐ and 18α‐11‐oxooleanolic acid derivatives
Authors: Wrzeciono U. , Zaprutko L. , Budzianowski J. , Wojtowicz H. , Dubowska D.
Published: May 2005

The 13C NMR spectra of five pairs of 18β‐ and 18°‐11‐oxooleanolic acid derivatives have been assigned. The chemical shifts of C‐12, C‐13, C‐17, C‐18 and C‐28 are of diagnostic value for the determination of the D/E junction stereochemistry.
Carbon‐13 and proton nuclear magnetic resonance studies of (E)‐ and (Z)‐ azetidinones
Authors: Hinz W. , Just G. , Sacripante G.
Published: May 2005

Carbon‐13 and proton NMR spectra of a variety of E and Z pairs of mono‐ and bi‐cyclic polysubstituted azetidinones have been measured. The effect of E/Z isomerism on the chemical shift values of ring carbon atoms and of proton substituents attached to the azetidinone nucleus is discussed.
Influence of the 1,1,3,3‐tetramethylguanidinyl substituent on the charge distribution in chlorobenzenes, studied by 35Cl NQR
Authors: Nogaj Boleslaw , Pruszyński Przemyslaw
Published: May 2005

35Cl NQR measurements were carried out on a series of chlorobenzenes with the 1,1,3,3‐tetramethylguanidinyl substituent {TMG = –N=C[N(CH3)2]2}. The substituent constants σp, σm, σaI, and σR for the TMG group were estimated from the relationships between the NQR resonance frequencies, νQ, and substituent constant values, σ. The νQ value for 2‐(4‐chlorophenyl)‐1,1,3,3‐tetramethylguanidine is the lowest observed for all chlorobenzenes, and arises from the strong positive conjugative effect of the TMG group. This effect is attributed to the possible resonance stabilization of the positive charge. Steric inhibition of resonance is observed for the ortho‐substituted isomers.
13C NMR spectroscopy of indole derivatives
Authors: Morales‐Ríos M. S. , Espiñeira J. , Joseph‐Nathan P.
Published: May 2005

The chemical shifts of 298 naturally occurring and synthetic compounds containing the indole chromophoric group are listed. Substituent effects on 13C chemical shifts (SCS) induced by substitution on the heteroaromatic five‐membered ring are discussed. The data provide a reference set for future 13C NMR investigations and highlight the need for unambiguous experimental evidence to resolve controversial assignments for differently substituted representative indole derivatives. Many original assignments have been changed, and values not considered to be unambiguously assinged are delineated. The 1 J(CH) values for the parent indole were measured.
13C and 1H NMR study of N‐5′‐methylsalicylideneanilines
Authors: Kishore K. , Sathyanarayana D. N. , Bhanu V. A.
Published: May 2005

The 13C and 1H NMR spectra of six N‐5′ ‐methylsalicylideneanilines have been studied. Correlations of the chemical shifts of C‐α (azomethine carbon) and C‐4′ with the σ, F, R, σ1 and σ parameters have been examined for N‐5′‐methylsalicylideneanilines, and also for N‐benzylideneanilines and N‐salicylideneanilines. The results suggest that the first compounds have a nearly planar conformation whereas the second and third type of derivatives have a twisted conformation.
Use of NOE difference spectra to determine configurations and conformations of imidate esters
Authors: Gallis David E. , Crist Delanson R.
Published: May 2005

A new method for determining conformations and configurations of imidate esters was developed based on NOE difference spectra in CDCI3. As a test of the method, methyl N‐methylacetimidate was determined to exist in the E configuration, ap conformation, in agreement with assignments by homoallylic coupling and dipole moment data. Methyl N‐tert‐butylformimidate, for which existing methods were not suitable, was also determined to exist as E‐ap. Two methyl benzimidates were investigated, the N‐methyl derivative 2, which was E‐ap, and the N‐tert‐butyl derivative 6, which exhibited an unusually easy E/Z isomerization at room temperature (Tc = 24°C). At ‐58 °C, resolved spectra showed the E/Z isomers of 6 in a 40:60 ratio. From NOE data (E)‐6 was determined to exist mostly as the ap conformer and (Z)‐6 as the sp conformer. These results, in agreement with chemical shift data, can be interpreted in terms of the unusual steric requirements of the tert‐butyl group.
NMR study of substituent effects in platinum(II) intercalating agents
Authors: Brownlee Robert T. C. , McFadyen W. David , O'Connor Maxwell J. , Rook Trevor J. , Roos Ian A. G. , Wakelin Laurence P. G.
Published: May 2005

A series of (4‐X‐thiophenolato) (2,2′:6′,2″‐terpyridine)platinum(H) complexes [X = H, F, Cl, Br, CH3, OCH3, NH2, N(CH3)2, NO2, COOCH3, CN, NH], which have potential as DNA intercalators, have been synthesized. 13C and 195Pt NMR spectra of these complexes have been obtained in both D2O and DMSO‐d6. The 195Pt shifts are highly sensitive to both solvent and distant substituent effects and span a chemical shift range of 72 ppm. The propagation and transmission of substituent effects within the complexes have been studied, and the 195Pt and thiophenolato C‐1 13C chemical shifts correlated with Hammett substituent constants, using the dual substituent approach. The results show that the (terpy)Pt—S— group is an effective π‐donor to the aromatic ring. Further, a normal substituent chemical shift effect is seen with the thiophenol C‐1, whereby electron‐withdrawing groups cause a decrease in electron density, whereas the platinum centre shows the reverse effect, i.e. electron‐withdrawing groups cause an increase in electron density. The latter effect has been explained in terms of a π‐polarization effect, with electron density from the terpyridine ligand being supplied to the platinum centre in response to demand by the thiophenol substituent.
Carbon‐13 NMR study of some triterpene hydrocarbons of the hopane group
Authors: Wilkins Alistair L. , Bird Peter W. , Jager Peter M.
Published: May 2005

The 13C NMR assignments of ten triterpene hydrocarbons of the hopane group are presented. Assignments for eight of the hydrocarbons are reported for the first time, whilst revisions to the published assignments of hopane and 17 α‐hopane are described.
NMR structural investigation of cellobiose and glucose
Authors: Lepri A. , Marchettini N. , Pogliani L. , Rossi C. , Ulgiati S.
Published: May 2005

T1(13C) NMR measurements on cellobiose and glucose in aqueous solutions at pH 5 at 276° and 296° K suggest that cellobiose molecules assume a nearly spherical shape in solution. NOE‐2D HETCOR and HOMCOR proton spectra of cellobiose confirm that cellobiose assumes a folded structure in aqueous solutions.
17O NMR spectra of methyl‐substituted 2‐oxo‐1,3,2‐dioxathianes
Authors: Mattinen Jorma , Pihlaja Kalevi
Published: May 2005

17O NMR chemical shifts of 2‐oxo‐1,3,2‐dioxathiane and 13 of its methyl‐substituted derivatives are reported. The chemical shifts depend strongly on temperature and to a much smaller extent on concentration. As a whole, however, they strongly support the predominance of chair conformations in these compounds and indicate some misinterpretations in a previous report.
Complexation of lanthanide(III) ions with a β‐diphosphorylated ligand: Nonamethylimidodiphosphoramide (NIPA). A 1H and 31P NMR study
Authors: Rubini P. , Nasr C. Ben , Rodehüser L. , Delpuech J.‐J.
Published: May 2005

Trivalent lanthanide ions form complexes of different stoichiometries with the bidentate ligand nonamethyl‐imidodiphosphoramide (NIPA). Depending on the method of preparation, compounds with two or three NIPA molecules may be obtained, which can be distinguished and characterized on the basis of their NMR spectra. The method of preparation for the tris‐chelates and an analysis of the isotropic paramagnetic shifts for these compounds are reported; the results allow the conclusion that the complexes in solution are isostructural along the lanthanide series. The same conclusion is drawn for the bis‐chelates. In both cases the contact and pseudo‐contact contributions to 31P shifts are important, whereas for the 1H nuclei the dipolar contribution is largely predominant.
Studies of 13C NMR spectra of 13C‐enriched cycloartenol biosynthesized from [1‐13C]‐, [2‐13C]‐and [1,2‐13C2]‐acetate. Revised 13C NMR spectral assignments of cycloartenol and cycloartanol and 13C NMR spectral support for the generally accepted skeleton formation mechanism of cycloartenol
Authors: Kamisak Wasuke , Honda Chie , Suwa Kiyoko , Isoi Koichiro
Published: May 2005

Previously proposed 13C NMR spectral assignments of cycloartenol (9,19‐cyclolanost‐24‐en‐3β‐ol) (1) and cycloartanol (9,19‐cyclolanostan‐3β‐3‐ol) (2) were re‐examined by means of 13C‐enrichment experiments and LIS measurement of 13C chemical shifts. Revised signal assignments are proposed for C‐7, C‐11, C‐16, C‐18, C‐21 and C‐28 of 1 and C‐7, C‐11, C‐12, C‐15 and C‐16 of 2. Experimental proof for the skeleton formation mechanism of 1 based on 13C NMR spectral findings is presented.
13C NMR study of the structures of open‐chain bis‐reissert analogues and their salts
Authors: Iyer Radhakrishnan P. , Ratnam Rakesh K. , Kulkarni Subodh P. , Zubair M. A. , Coutinho Evans C. , Sonaseth Mariam S. , Gopalan Balasubramanian
Published: May 2005

The structures of open‐chain bis‐Reissert analogues and their salts were investigated using 13C NMR spectroscopy. Evidence is presented to show that the former exists in the acyclic form in solution. Detailed structural studies and the 13C NMR data clearly show that, in solution, the open‐chain bis‐Reissert salt analogues exist predominantly as the amino tautomer.
Carbon‐13 spectra of some heterocyclic analogues of biphenylene
Authors: MacBride J. A. Hugh , Leow Mei Ling , Wright (the late) Peter M. , Kilcoyne John P. , Wakefield Basil J.
Published: May 2005

The 13C chemical shifts for 2,7‐, 1,8‐ and 1,6‐diazabiphenylenes are reported, together with some coupling constants and the 13C chemical shifts of a benzothiophene analogue of biphenylene. The results can be explained by the existence of a paramagnetic ring current in the four‐membered ring of the nitrogen‐containing compounds which is absent in the case of the benzothiophene. A possible explanation is offered.
Long‐range 13C1H spin—spin coupling constants in the conformational analysis of formyl derivatives of furan and thiophene
Authors: Benassi Rois , Folli Ugo , Mucci Adele , Schenetti Luisa , Taddei Ferdinando
Published: May 2005

Long‐range coupling constants, nJ(C, H), involving the formyl proton or carbon and the carbons or protons of the heterocyclc ring, were measured in the two isomeric formyl‐furans and ‐thiophenes by employing coupled 13C NMR spectra. In furan‐2‐carboxaldehyde these coupling constants, obtained in solutions of different polarity, show conformational dependence and quantitatively reproduce the trend of conformer populations obtained from proton‐proton coupling constants. Even in thiophene‐2‐carboxaldehyde, 3J(C, H), where H is the formyl proton, shows that the very biased equilibrium is further shifted toward the S,O‐cis form in polar media. For the 3‐formyl derivatives the changes of nJ(C, H) in different solvents are small, at the limit of experimental error; even so, comparison with the values measured for 4‐iodofuran‐ and 4‐iodothiophene‐3‐carboxaldehyde, which show an equilibrium significantly dependent on solvent polarity, enables one to verify that in these derivatives the X,O‐trans form, prevailing in the equilibrium mixture, increases with increasing solvent polarity. From a least‐squares analysis of the experimental values, the conformer populations in the different solvents and the coupling constants of the separate conformers were estimated. The coupling constants obtained show the effectiveness of each nJ(C, H) in the conformational analysis of these compounds. Larger changes, as a function of conformer populations, are expected for 3J(C, H) relative to the formyl proton, and this proves to be the observable quantity which best demonstrates small changes in the conformational equilibrium. The thermodynamic aspects of the equilibrium for the 3‐formyl derivatives are discussed and, by employing classical reaction‐field theory, it is tentatively shown that the increase of the less polar X,O‐trans form in polar media should be due to the fact that quadrupolar contributions prevail over dipolar effects.
Aromatic ring currents in benzotriptycenes, studied by high‐resolution deuterium NMR at high fields
Authors: Bastiaan E. W. , Wegman M. A. M. , MacLean C.
Published: May 2005

In order to study the aromatic ring currents in triptycene and tribenzotriptycene, the magnetic susceptibility anisotropies of these molecules have been determined by the NMR analogue of the Cotton‐Mouton effect: Δ χ(triptycene) = 24.0 x 10‐34 m3 (1.91 x 10‐28 emu), Δ χ(tribenzotriptycene) = 44.5 x 10‐34 m3 (3.54 x 10‐28 emu). These values are well predicted from a model of independent fragment molecules, showing that the ring currents in the rings of triptycene and tribenzotriptycene are essentially the same as in planar aromatic molecules.
Rate of degenerate rearrangement of the 2‐methyl‐2‐norbornyl cation studied by 13C selective pulse transfer and two‐dimensional NOESY spectroscopy
Authors: Baine Peter , Domenick Robert L. , Servis Kenneth L.
Published: May 2005

The rate of the degenerate 6,1‐hydride shift and rearrangement of the 2‐methyl‐2‐norbornyl cation has been determined using selective pulse transfer experiments and 2D NOESY experiments over the temperature range 200–220 K. Least‐squares analysis of the data gives a free energy of activation of 11.3 kcal mol−1. The results are compatible with the presence of σ‐delocalization in the 2‐methyl‐2‐norbornyl cation.
2D NMR studies of the phenyldichloroarsine—british anti—lewisite adduct
Authors: Dill Kilian , Adams Earle R. , O'Connor Richard J. , McGown Evelyn L.
Published: May 2005

One‐ and two‐dimensional NMR spectroscopy was used to determine the structure of the phenyldichloroarsine‐British anti‐lewisite adduct. The major component had the hydroxymethyl group in the anti orientation with respect to the phenyl ring on the arsenous atom. This structure was based on the chemical shifts of the 1H and 13C resonances and on the respective homonuclear coupling constants.
Structure elucidation of a hexahydrocannabinol derivative via 13C13C homonuclear correlation and 1H13C heteronuclear correlation with proton detection
Authors: Zetta Lucia , De Marco Antonio , Anklin Clemens , Cornia Mara , Casiraghi Giovanni
Published: May 2005

Two‐dimensional carbon‐carbon correlated spectra (2D‐INADEQUATE) and proton‐carbon correlated spectra obtained with proton detection have been used to determine the absolute configuration and conformation of a hexahydrocannabinol derivative obtained with highly stereocontrolled synthesis. From the proton‐proton coupling constants the junction between rings B and C was found to be trans and the relative stereodisposition of C‐10a, C‐9 and C‐6a was deduced to be R.
13C NMR of diterpenes: Use of the C‐19 methyl group as a probe for locating a tetrasubstituted double bond
Authors: Taran Martine , Miguel Bernadette Arreguy‐San , Delmond Bernard , Petraud Michel , Barbe Bernard
Published: May 2005

The 13C NMR spectra of diterpenic derivatives having pimarane, isopimarane and the (13S) rosane skeleton have been recorded. This analysis has shown that the chemical shift of the 19‐CH3 group depends on the position of the tetrasubstituted double bond in these skeletons. The C‐19 methyl group can be used as a probe for distinguishing the isopimarane from the rosane skeleton.
Unequivocal assignment of the position of sulphonation in DL‐camphor by 1H and 13C NMR spectroscopy
Authors: Stanley P. D. , Cremlyn R. J. , Nangle J. , Swinbourne F. J.
Published: May 2005

The 1H and 13C NMR spectra of a sulphamoyl derivative of DL‐camphor have been examined. The unequivocal assignment of the position of substitution has been achieved by the attached proton test, 2D correlation spectroscopy and NOE difference spectroscopy.
13C NMR spectra of substituted pyridine N‐oxides. Substituent and hydrogen bonding effects
Authors: Brycki B. , Nowak‐Wydra B. , Szafran M.
Published: May 2005

Aromatic 13C chemical shifts of 4‐ and 3‐substituted pyridine N‐oxides in aprotic and protic solvents are reported and discussed. Changes in chemical shifts caused by hydrogen bonding and protonation are much smaller than those induced by a substituent, and are not related to the pKa values of N‐oxides. Since the effect of hydrogen bonding is not in the same direction as that due to the substituent effect, the estimation of proton transfer from measured chemical shifts is not possible in complexes of pyridine N‐oxides with trifluoroacetic acid. A linear correlation is obtained between the ipso carbon substituent chemical shifts of 4‐ and 3‐substituted pyridine N‐oxides and mono‐substituted benzenes, which supports the suggestion that electronic factors other than Δq are more important for the ipso carbon.
Distinction of 15N resonances based on differences in small 15N, 1H coupling constants. An application of 1H‐decoupled INEPT experiments
Authors: Glemarec C. , Remaud G. , Chattopadhyaya J.
Published: May 2005

A modified 1H‐decoupled INEPT pulse sequence has been used for assigning 15N resonances, based on differences in small 15N, 1H coupling constants (1–12 Hz). Both enhancement and distinction of the 15N lines are achieved. The usefulness of this method is demonstrated for wyosine triacetate and caffeine.
NMR spectra of the porphyrins. 34—Determination of the conformational equilibria of monosubstituted piperidines at room temperature using cobalt(III) porphyrin shift reagents
Authors: Abraham Raymond J. , Medforth Craig J.
Published: May 2005

The 1H and 13C NMR spectra of piperidine and eight monosubstituted piperidines and their spectra with cobalt(III) mesotetraphenylporphyrin chloride (CoTPPCl) and cobalt(III) octaethylporphyrin chloride (CoOEPCl) were assigned using a range of NMR techniques. When complexed to the porphyrin shift reagent the axial and equatorial conformers were in slow exchange at room temperature, allowing the determination of conformational equilibria and substituent chemical shifts (SCS).

Conformational free energy differences (−ΔG°, kcal mol−1) obtained for 4‐substituted piperidines using CoOEPCl at 298 K were 0.5 (X = Br), 0.7 (X = OH), 0.8 (X = carbethoxy), 1.8 (X = Me) and > 1.6 (X = Ph). These were in good agreement with literature values. For CoTPPCl the corresponding values were −0.2 (axial conformation favoured), 0.3, 0.7, 1.4 and > 1.6, indicating that an axial orientation of the 4‐substituent was more favoured than with CoOEPCl. This difference was rationalized in terms of steric and electrostatic interactions between the piperidine substituent and the phenyl rings of CoTPPCl. In both cases proton and 13C SCS values were in good agreement with those in the literature.

With 1‐, 2‐ and 3‐methylpiperidines unusual results were obtained for both porphyrins. For 3‐methylpiperidine −ΔG° was only 0.8 kcal mol−1 compared with a literature value of 1.6 kcal mol−1, whilst for 1‐ and 2‐ methylpiperidine reduction of the shift reagent to cobalt(II) occurred. With 1‐methylpiperidine the reduction was complete and no complexation was observed, but only some of the shift reagent was reduced by 2‐methylpiperidine and the remaining shift reagent complexed to the amine.
Structure and conformation of α‐bromobutyrolactones in the solid state and solution
Authors: Gharbi‐Benarous Josyane , Dana Gilbert , Philoche‐Levisalles Michele , Bois Claudette
Published: May 2005

X‐ray diffraction of a single crystal of 4β‐phenyl(or mesityl)‐3β‐methyl‐2α(or 2β)‐bromobutyrolactone confirmed the envelope conformation of the butyrolactone unit. In both cases the aryl group is equatorial and the methyl group is axial; the 2α‐bromine is axial and the 2β‐bromine is equatorial. The coupling constants observed by 1H NMR for a series of α‐bromobutyrolactones show two types: with a mesityl group at C‐4 there is always a pure conformation with an equatorial mesityl group; with a phenyl group at C‐4 the two reverse envelope forms are possible, the favoured effects being equatorial Ar > axial Br > equatorial Me. In the generalized Karplus equation a strong influence of the relative orientation of the bromine and the carbonyl on the corresponding electronegativity parameters was observed. These parameters were evaluated by means of the electronegativity group concept and weighted by a stereochemistry‐dependent coefficient (cis or trans).
ESR and ENDOR investigations of phenanthrenesemiquinones
Authors: Stegmann Hartmut B. , Dao‐Ba Hoang , Mäurer Manfred , Scheffler Klaus , Buchner Hans , Hartmann Erwin , Mannschreck Albrecht
Published: May 2005

A series of phenanthrenesemiquinone–diphenylthallium complexes were prepared in solution from the corresponding quinones. ESR, ENDOR and TRIPLE spectra provided the proton coupling constants and the unambiguous assignment to distinct molecular positions. The thallium splitting becomes considerably less negative if the semiquinones are twisted by steric hindrance in the 4‐ and 5‐positions. On the other hand, substitution in the 1‐ and 8‐positions renders aTI more negative. These results are interpreted in terms of steric hindrance of the ion‐pair solvation.
Unambiguous assignment of the 13C NMR spectra of methylindoles
Authors: Morales‐Ríos M. S. , Del Río R. E. , Joseph‐Nathan P.
Published: May 2005

The 13C NMR spectra of all possible indoles substituted with one, two or three methyl groups on the pyrrole ring were assigned from heteronuclear two‐dimensional 13C/1H contour plots and homonuclear hydrogen‐hydrogen decoupling experiments at a specific concentration of 0.83 M in CDCl3 and in DMSO‐d6. The results confirm controversial assignments for some compounds, and provide the assignments for those compounds not previously studied by this technique. In addition, deuterium/hydrogen NMR isotope effect on 13C chemical shifts (DHIECS) for indoles, wherein the labile NH was partially exchanged to ND, are reported. In this way DHIECS values over two, three, four and five bonds were measured. The results in each solvent are discussed in terms of the number of bonds between the exchanged hydrogen and the observed carbon, and also according to their geometric dependence. This provides some evidence of the vibrational origin of the DHIECS.
13C NMR assignment of dammarane triterpenes and dendropanoxide: Application of 2D long‐range 13C1H correlation spectra
Authors: Tori Motoo , Matsuda Reiko , Sono Masakazu , Asakawa Yoshinori
Published: May 2005

The 13C NMR chemical shifts of some dammarane‐type triterpenes, produced by oxidation of dammaran‐20(S)‐ol and 20(S)‐hydroxydammaran‐3β‐yl acetate with m‐chloroperbenzoic acid, were assigned by complete analysis of these compounds using 2D long‐range 13C1H correlation spectra and 2D INADEQUATE; it was found necessary to revise previous assignments. The 13C NMR signals of dendropanoxide were also analysed by 2D techniques including HHC relayed 13C1H correlation spectra.
13C NMR and 1H NMR chemical shifts of bis(1,1‐dimethylethyl) disulfide and bis(1,1‐dimethylethyl) trisulfide and their oxide derivatives
Authors: Freeman Fillmore , Lee Choonsun
Published: May 2005

The 13C NMR and 1H NMR spectra of bis(1,1‐dimethylethyl) disulfide and bis(1,1‐dimethylethyl) trisulfide and their oxygenated derivatives, including sulfinothioic acid S‐esters and sulfonothioic acid S‐esters, have been studied. Deshielding βSO and β effects and shielding γSO and γ effects are observed. The NMR spectra of tert‐butyl polysulfides and the influences of sulfur atoms are also compared and discussed.
Application of two‐dimensional NMR spectroscopy in the determination of solution conformation of nucleic acids
Authors: Hosur R. V. , Govil Girjesh , Miles H. Todd
Published: May 2005

Two‐dimensional NMR has developed into an important tool for the study of solution structures of nucleic acids. The conformational information is generally derived from the three bond coupling constants (J) and interproton distances (r). Strategies have been developed to obtain J values using COSY and J‐resolved spectroscopy. Estimation of interproton distances involves measurement of NOESY build‐up curves as a function of mixing time. This information can be coupled with structural refinement techniques to obtain the three‐dimensional structure of nucleic acids. Here we have described the current status of this important field with particular reference to advancements in applications to DNA structures.
Application of 1H NMR bi‐selective relaxation times to conformational analysis in solution
Authors: Sugiura Makiko , Takao Narao , Fujiwara Hideaki
Published: May 2005

The usefulness of 1H bi‐selective relaxation times (T) and selective relaxation times (T) for structure and conformation determination is emphasized. A pulse sequence has been devised which provides the apparent observed T. The cross‐relaxations (σij) or Fij values are derived from the observed T and T values. The σij values can be correlated with the HH distances (rij) and can be used for conformational analysis or structure determination. The Fij values, which indicate the fractional contribution to the dipolar relaxation of proton i via the interaction with proton j(i ≠ j), can be compared with the NOE values. 2‐Vinylpyridine was chosen as a model compound and three types of T1 values were measured for its protons. Its conformation in CDCl3 solution is discussed based on the correlation between the σij obtained and the rij values. A conformational equilibrium is suggested.
Utility of 1H/2H isotope shifts for the 13C NMR assignments of indole derivatives
Authors: Morales‐Ríos M. S. , Joseph‐Nathan P.
Published: May 2005

The deuterium/hydrogen NMR isotope effects on the 13C chemical shift (DHIECS) of the cycloalkano[b]indoles 1,2,3,4‐tetrahydro‐9H‐carbazole, 3‐tert‐butyl‐1,2,3,4‐tetrahydro‐9H‐carbazole and 1,2,3,4‐tetrahydrocyclopent‐[b]indole, wherein the labile NH was partially exchanged to ND, were measured at a concentration of 0.83 M in CDCI3 and in DMSO‐d6 solutions. The DHIECS values show defined trends that allow definitive 13C NMR assignments. The isotope effects over three and four bonds for the sp3 hybridized carbons are linearly interdependent, even when one of these isotope effects becomes negative.
High‐resolution 1H and 13C NMR spectroscopy of some hydrazo compounds
Authors: Al‐Rawi J. M. A. , Khayat M. A. R.
Published: May 2005

o‐Benzenediazonium carboxylates couple with methylene‐active compounds to yield hydrazo derivatives with high purity. The 1H and 13C NMR data of eleven such products are presented and analysed. The predominance of the hydrazo over the azo form is consistent with accepted criteria. Furthermore, evidence for the preference of the carbethoxy group over the acetyl group for intramolecular hydrogen bonding is suggested.
Proton nuclear magnetic resonance studies of dibenzo‐p‐dioxins: Substituent effects
Authors: Ashley David L. , Reddy V. Vikram , Patterson Donald G.
Published: May 2005

High‐resolution proton nuclear magnetic resonance through heptachlorinated dibenzo‐p‐dioxins are presented. Chemical shifts from dioxins that were synthesized separately are used to assign congeners formed in mixtures. Linear multiple regression analysis was applied to the chemical shift results and the model yielded excellent shift predictability once substituent interactions had been included in the analysis. The average deviation from experimental values was 0.004 ppm. The intra‐ring substituent effects can be explained by a combination of through‐space and ring current effects. Inter‐ring substituent effects showed a dependence on distance, but the reason for this trend is not clear. These measurements demonstrate a reproducible chemical shift effect over nine bonds.
Phosphorus–nitrogen compounds. Part 59. Aromatic carbon‐13 NMR spectra of phenyl‐substituted cyclotriphosphazatrienes. Second‐order effects with phosphorus‐31 nuclei
Authors: Deutsch W. Francis , Parkes Harold G. , Shaw Robert A.
Published: May 2005

The 13C NMR spectra were obtained for the geminal series N3P3Cl6−nPhn (n = 2, 4, 6) and for the mono spiro series N3P3Ph2[X(CH2)n Y]Cl2 (X = Y = O, n = 2, 3, 4; X = Y = NH, n = 2, 3, 4; X = Y = NMe, n = 2, 3; X = O, Y = NH, n = 3, 4; X = NH, Y = NMe, n = 2, 3; X = O, Y = NMe, n = 2). Multiplet structures were observed in the 13C NMR spectra of N3P3Ph2[HN(CH2)3NH]Cl2 at 0°C. The complexity of these resonances could be altered by a change in temperature. These observations have been rationalized in terms of second‐order interactions with remote phosphorus nuclei, which can be systematically altered with temperature. Inductive and resonance substituent coefficients have been calculated using the dual substituent parameter method from the relative shelding of the meta (C‐3) and para (C‐4) nuclei in the phenyl ring.
NMR study of backbone rearrangements in gibberellins
Authors: Avent Anthony G. , Hanson James R. , d'Oliveira Bras H.
Published: May 2005

The 1H and 13C NMR spectra of the rearrangement product of gibberellic acid obtained in concentrated sulphuric acid confirm the structure which had previously been assigned by chemical degradation. The triene produced from methyl gibberellate by the action of methanolic hydrogen chloride is shown to possess the 5α, 6β‐H stereochemistry. The incorporation of deuterium into the latter is described.
Epoxidation‐induced shifts in the carbon‐13 NMR spectra of steroids: Lanostane derivatives
Authors: Martynow Jacek , Paryzek Zdzisław
Published: May 2005

The 13C chemical shifts of triterpenoidal olefins and epoxides related to lanosterol are described and discussed. The epoxide function located in the central part of the tetracyclic steroidal skeleton allows the evaluation of epoxidation‐induced shifts (EIS) for several carbons. The most characteristic and valuable for stereochemical assignments are the EIS values for γ‐carbons C‐1, C‐5, C‐12, C‐19 and C‐28 in 8α,9α‐epoxides, and C‐1 and C‐19 in 9α,11α‐epoxides. The C‐α effect (EIS −55 to −79 ppm) is found to be susceptible to minor conformational distortions of the molecular framework. Characteristic signals are discussed in terms of their predictive value for each group of analysed compounds.
2H NMR study of the behaviour of water in a reversed micellar system. Hydrogen bond breaking and clathrate formation by an inhalation anaesthetic
Authors: Yoshino Akihiro , Yoshida Tadayoshi , Takahashi Kensuke
Published: May 2005

The behaviour of water in the reversed micelles of the glycerol α‐monooleate (GMO)–decane‐2H2O system was investigated by deuteron nuclear magnetic resonance. The chemical shifts (δ) and the spin–lattice relaxation times (T1) of heavy water were found to be dependent on temperature. The temperature dependence of the T1 and δ values reveals that the structural change in heavy water induced by the inhalation anaesthetic enflurane is very different below and above ca. 300 K. Below ca. 300 K a cage of a water polyhedron builds up around an enflurane molecule. Above ca. 300 K there is no water polyhedron cage because of the cleavage of the hydrogen bonds in the polyhedron water, and some of the water molecules are tightly adsorbed on the enflurane molecules.
Two‐dimensional NMR studies of Pt(2‐methallyl)(SnCl3)(styrene). Recognition and interpretation of simultaneous exchange processes via 1H noesy
Authors: Ammann Christian , Pregosin Paul S. , Rüegger Heinz , Grassi Mariella , Musco Alfredo
Published: May 2005

The 1H NMR spectrum of Pt[η3‐CH2C(CH3)CH2](SnCl3)(PhCHCH2) (1), which is complicated by the existence of two isomers, has been interpreted using (195Pt, 1H)‐INVERSE, J‐resolved, COSY‐90 and NOESY two‐dimensional methods. The two isomers are shown to be involved in slow exchange processes, and one intermediate in the exchange, Pt[CH2C(CH3)CH2](SnCl3) (4), has been identified and characterized via 1H, 13C, 119Sn and 195Pt spectroscopy. NOESY measurements show that neither 1 nor 4 is involved in an η3 →η1 isomerization, so that 4 must be involved in the dynamics with 1 via loss of a tin‐containing fragment, presumably SnCl3−. Uncoordinated PhCHCH2 has been detected in solution and shown to exchange with the complexed PhCHCH2 in both isomers of 1.
1H and 13C NMR studies on mono‐ and polybrominated biphenyls
Authors: Anklam Elke
Published: May 2005

The 400 MHz 1H and 13C NMR parameters of 15 mono‐ and polybrominated biphenyls were determined and compared with those of the corresponding chlorinated biphenyls.
Establishing long‐range connectivities in polynuclear aromatics through the use of two‐dimensional MLEV‐17‐based isotropic mixing
Authors: Johnston Milton D. , Martin Gary E.
Published: May 2005

A method for observing long range 1H;1H coupling pathways of polynuclear aromatics using the HOHAHA (TOCSY) experiment is described. The method affords a potentially superior alternative to the more established long range optimized COSY (LRCOSY) experiment. Hexahelicene derived phenanthro[3′,4′:3,4]phenanthro[2,1‐b]thiophene is employed as a model compound to demonstrate the method.
13C NMR studies of cis–trans isomerization of N‐benzylidene‐propyl‐ and ‐substituted aryl‐amines induced by a lanthanide shift reagent
Authors: Al‐Rawi Jasim M. A. , Saleem L. M. N.
Published: May 2005

The 13C chemical shifts of cis‐ and trans‐benzylidenepropylamine and substituted benzylideneanilines were analysed after additons of Eu(fod)3. The cis/trans ratio increases as the amount of lanthanide shift reagent increased. The cis isomers showed large lanthanide‐induced shifts, whereas the trans isomers showed little or no effect.
13C nuclear magnetic resonance study of some phosphinolipids: Assignments and conformational studies
Authors: Kallinowski Georg , Vogt Walter
Published: May 2005

13C chemical shifts and 31P, 13C spin‐spin coupling constants are reported for six model phosphinates and eight synthetic phosphinolipids. The complex spectra of the synthetic phosphinolipids could be assigned from increments and couplings derived from the model compounds. Based on these investigations the 3J(PC) couplings of 7–15 Hz indicate a preferential trans orientation of the respective head‐group carbon relative to the phosphorus. This behaviour is similar to that of natural phosphatidylcholine lipids.
Studies on the benzoxazine series. 2—Preparation and1H and13C NMR structural study of some substituted 1,2‐dihydro‐4H‐3,1‐benzoxazines
Authors: Neuvonen Kari , Pohtola Riitta , Pihlaja Kalevi
Published: May 2005

In addition to the parent compounds, nine methyl‐substituted 1,2‐dihydro‐4H‐3,1‐benzoxazines with and withoutN‐methyl substitution were prepared. The chain tautomer could only be detected in the case of 1,2‐dihydro‐2‐(p‐nitrophenyl)‐4H‐3,1‐benzoxazine in solution. The configurational and conformational assignments were based on1H and13C NMR data. The calculations of the methyl substituent effects on the heterocyclic ring (half‐chair structure) carbons gave a good fit between the observed and calculated shifts and made in possible to estimate that 1,2‐dihydro‐4‐methyl‐4H‐3,1‐benzoxazine is a 75:25 and itsN‐methyl derivative a 69:31 mixture of the 4eq′‐ and 4ax′‐ forms. 1,2‐Dihydro‐trans‐1,2,4‐trimethyl‐4H‐3,1‐benzoxazine is also not conformationally homogeneous, but is a 43:57 mixture of the 2eq,4ax′‐ and 2ax,4eq′‐ forms. A comparison of the13C chemical shift correlations with those of 3,4‐dihydro‐2H‐1,3‐benzoxazines also improves the structural knowledge about the latter series. Whereas theN‐methyl groups in 3,4‐dihydro‐2H‐1,3‐benzoxazines are axially orientated, model calculations reveal that theN‐methyl substitutions in the title compounds can be orientationally heterogeneous.
Synthesis and conformational analysis of dibenzodithiocin derivatives
Authors: Sohár P. , Kövesdi I. , Szabó J. , Katócs Á. , Fodor L. , Szücs E. , Bernáth G. , Tamás J.
Published: May 2005

N‐(3,4‐Dialkoxyphenylthiomethyl)aroylamides (la, b) reacted with phosphoryl chloride to give not only the expected 4H‐ and 2H‐1,3‐benzothiazine derivatives (4a, b and 5a, b), but also dibenzodithiocins of new (dibenzo[d,g][1,3]dithiocins 2a, b) and known (dibenzo[b,f][1,5]dithiocins 3a, b) types. The analogous reaction of the 4‐methylaroylamide 8a furnished the 4H‐1,3‐benzothiazine 9a, the dibenzo[b, f][1,5]dithiocin derivative 10a and benzonitrile. In contrast, 8b (the chloro analogue of 8a) furnished only benzonitrile and bis(4‐chlorophenylmercapto)methane (11). The structures of the new compounds were confirmed by IR, 1H and 13C NMR, and (in part) by mass spectrometry. Temperature‐dependent 1H NMR studies were used for the conformational analysis of 2a and its disulphone 6a; the nature and free enthalpies of activation of the two different conformational motions occurring at higher temperatures were determined.
13C NMR study of 2‐iodoso‐ and 2‐iodoxy‐benzoic acids and their sodium salts
Authors: Katritzky Alan R. , Duell Bradley L. , Gallos John K. , Durst H. Dupont
Published: May 2005

The 13C NMR spectra for selected 2‐iodosobenzoic acids, their sodium salts and the sodium salts of the corresponding iodoxybenzoic acids were measured and carbon assignments made using 2D and NOE experiments and relaxation times. Iodoso and iodoxy groups deshielded the ipso‐carbon in these compounds by approximately 25 and 55 ppm, respectively, relative to the corresponding iodo compounds. The 13C NMR spectra of the 2‐iodosobenzoate anions were almost identical with those of the corresponding free acids, both possessing cyclic structures. The iodoxybenzoic acids are either insoluble in, or oxidize, suitable NMR solvents (i.e. DMSO‐d6, DMF‐d7). The cyclic structure postulated for iodoxybenzoate anions is supported by their 13C chemical shifts.
Substituent chemical shifts in NMR. Part 4—1H SCS in some 2‐substituted norbornanes and bornanes
Authors: Abraham Raymond J. , Barlow Andrew P. , Rowan Alan E.
Published: May 2005

The 1H chemical shifts and substituent chemical shifts (SCS) were recorded for several monosubstituted norbornanes and bornanes. The observed substituent effects are generally similar for the two ring systems, but difter considerably from those observed for the cyclohexanoid systems in steroids. A consistent trend for the eclipsed C‐2—C‐3 fragment in this ring system is that all the substituents produce the largest SCS on the trans oriented proton, rather than the spatially nearer cis oriented proton. Indeed, for the OH substituent these SCS are opposite in sign, that for the cis oriented proton being negative (i.e. to high field). This trend is not observed in the cyclo‐hexane system, in which the distance dependence of the vicinal SCS is as expected. The major cross‐ring SCS are of the 2‐endo substituents with the C‐6 protons, giving a large positive SCS at the 6n proton and a small negative SCS at the 6x proton. This trend is very similar to that observed in the cyclohexane ring (axial‐axial SCS), and suggests a similar electric field mechanism.
Improvement of carbon‐detected H,H‐TOCSY experiments by employing a DEPT transfer
Authors: Kessler H. , Gemmecker G. , Köck M. , Osowski R. , Schmieder P.
Published: May 2005

A new version of the 2D combination of TOCSY and H,C‐COSY is proposed which uses the DEPT technique for the heteronuclear transfer. Hence the resulting 2D spectrum can be easily corrected to pure absorption mode for optimum resolution in both dimensions. In contrast to an earlier published version with a partially refocused INEPT sequence and delayed heteronuclear decoupling in F2, the new variant does not generate any base‐line distortions interfering with interesting signals. In addition, experimental spectra obtained from cyclosporin A and a cyclic hexapeptide also show improved sensitivity compared with the INEPT version. In all these experiments, the information about direct HC connectivities is lost owing to the TOCSY transfer preceding the heteronuclear transfer. This information can, however, be provided by a version with only partial heteronuclear decoupling in F1, which can be easily obtained by shifting the refocusing 180° 13C pulse out of the centre of t1. Thus all couplings can be reduced to a fraction of their original value, as long as the large 1J coupling still causes a visible doublet splitting in the 2D spectrum. The reduced heteronuclear couplings lead to a spectrum which is easy to interpret, since the resulting small splittings of the direct cross‐peaks are unlikely to interfere with other signals. In addition, all long‐range couplings in F1 are also scaled down, thus causing less line broadening and therefore higher sensitivity.
13C CP‐MAS study of the polymorphs of naphthazarin and of some methyl derivatives
Authors: Olivieri Alejandro , Paul Iain C. , Curtin David Y.
Published: May 2005

The high‐resolution 13C solid‐state NMR spectra of naphthazarin polymorphs and some of its derivatives having methyl substituents are discussed. Differences observed between the spectra of the A and B forms and that of the C modification of naphthazarin are explained by invoking hydrogen‐bonding effects. The 2‐methyl and 2,3‐dimethyl derivatives show spectra consistent with their x‐ray‐determined structure as being mainly composed of the tautomer bearing the substituents on the quinonoid ring. The 2,7‐dimethyl‐substituted compound undergoes a fast intramolecular proton migration at room temperature between tautomers present in nearly equal amounts.
Selection and chromatographic removal of paramagnetic relaxation reagents
Authors: Herzog H. , Gosciniak B. , Buddrus J.
Published: May 2005

Both Cr(acac)3 and Fe(acac)3 can be used as relaxation reagents in INADEQUATE 13C NMR measurements. Removal of the reagents is accomplished by silica gel chromatography, the choice of the eluent being dependent on the polarity of both the reagent and the organic compound.
Complete assignments of the 1H and 13C NMR spectra of testosterone and 17α‐methyltestosterone and the 1H parameters obtained from 600 MHz spectra
Authors: Hayamizu Kikuko , Kamo Osamu
Published: May 2005

Complete sets of 1H chemical shifts and spin coupling constants of testosterone and 17α‐methyltestosterone were determined by analysis of the 600 MHz 1H NMR spectra. The spin coupling constants of the two compounds have similar values, but the substitution of a methyl group at the 17α‐position changes the 1H chemical shifts of some protons on the C and D rings: low‐field shifts for H‐12α, H‐14α and H‐16α and high‐field shifts for H‐12β and H‐16β. The two‐dimensional 1H‐1H COSY and NOESY methods were used for unambiguous assignments, including those for the signals of H‐16α and H‐16β which are interchanged in the present paper from the assignment reported previously. Two‐dimensional 1H‐13C shift correlated spectroscopy was also used to complement the 1H and 13C assignments. The effect on the 13C chemical shifts of methyl substitution at the 17α‐position is briefly discussed.
Two‐dimensional NMR spectral study of the tautomeric equilibria of D‐fructose and related compounds
Authors: Jaseja Mahesh , Perlin Arthur S. , Dais Photis
Published: May 2005

The use of two‐dimensional NMR techniques and spin simulation afforded a detailed set of chemical shift and spin–spin coupling data for the main tautomeric forms of D‐fructose in dimethyl sulfoxide and aqueous solutions. Differences in vicinal coupling parameters for β‐D‐fructofuranose in the two solvents are taken as evidence that this tautomer incorporates intramolecular hydrogen bonding in dimethyl sulfoxide, which helps to account for its exceptional prominence in this solvent. The enhanced proportion of α‐D‐fructofuranose in dimethyl sulfoxide over that in water also receives comment. Also described are corresponding data from NMR measurements on the tautomeric equilibria of disaccharides that contain a D‐fructose reducing‐end residue, and of the homomorphic ketose, L‐galacto‐2‐heptulose, i.e. structurally related compounds that may entail different kinds of hydrogen‐bonding possibilities. Evidence indicating the presence of extensive inter‐residue hydrogen bonding within the individual tautomers of the disaccharide turanose is provided by the pattern of hydroxyl proton chemical shifts in dimethyl sulfoxide.
2D NMR studies on mortonin A, C and D. Unambiguous assignment of 13C chemical shifts
Authors: Rodríguez‐Hahn L. , Jiménez M. , Díaz E. , Jankowski K. , Davoust D. , Fagerness P.
Published: May 2005

High‐field 2D NMR studies of mortonins were performed at 500 MHz (1H) and 125 MHz (13C). Unambiguous assignment both of the 13C data to the carbon skeleton and that of the proton chemical shifts in these molecules was achieved, together with the establishment of the configuration of the asymmetric centres. Some previously reported signals have been reassigned.
13C NMR study of quipazines
Authors: Joseph‐Nathan P. , García‐Martínez C.
Published: May 2005

The complete assignment of the 13C NMR spectra of a series of biologically active quipazines substituted at position C‐5, C‐6 or C‐7 of the quinoline moiety provides evidence for a strong conjugation between the π‐electron cloud of the pyridine ring and the nitrogen lone pair of the piperazinyl residue. The SCS values of these quipazines are compared with those of the analogous quinolines, and their deviations are discussed in terms of conjugation effects.
13C,1H spin–spin coupling. X—Norbornane: A reinvestigation of the karplus curve for3J(13C,1H)
Authors: Aydin Rafet , Günther Harald
Published: May 2005

13C,2H spin–spin coupling constants over one, two and three bonds were measured from the 100‐MHz13C NMR spectra of deuteriated isotopomers of norbornane‐d1, (1) and fenchane‐2‐d1(2) and also of a number of mono‐deuteriated alkyl‐substituted adamantanes. The magnitudes of the correspondingJ(13C,1H) values derived from these data by application of the well known relationshipJ(X,1H) = 6.5144J(X,2H) are discussed with respect to the structural data for the hydrocarbons, which were taken from force field calculations with the Allinger MM2 method. In particular, the dihedral angle dependence and the Karplus curve for3J(13C,1H) are investigated. Coupling constants calculated by the FP‐INDO method are compared with the experimental data, and the effect of substitution by additional CC bonds in α‐, β‐ and γ‐positions of the13C‐αC‐βC‐γH bond fragment is elucidated. If substituent effects that arise through branching and methyl substitution in 1 and 2 are taken into account for dihedral angles ϕ > 90°, one derives3J(13C,1H) = 4.50 − 0.87 cos ϕ + 4.03 cos 2ϕ withJ(0°) = 7.7,J(60°;) = 2.0 andJ(180°) = 9.4 Hz.
1D and 2D NMR study of some allenic carotenoids of the fucoxanthin series
Authors: Englert Gerhard , Bjørnland Terje , Liaaen‐Jensen Synnøve
Published: May 2005

The allenic carotenoid all‐trans‐(3S,5R,6S,3′S,5′R,6′R)‐19′‐butanoyloxyfucoxanthin, isolated from the marine chrysophyte Pelagococcus subviridis, and its 9′‐cis isomer, obtained in 45% yield on iodine‐catalysed stereomutation, were submitted to a detailed 1H and 13C NMR analysis. For comparison, all‐trans‐fucoxanthin [(3S,5R,6S3′S,5′R,6′R)‐5,6‐epoxy‐3,3′,5′‐trihydroxy‐6′,7′‐didehydro‐5,6,7,8,5′,6′‐hexahydro‐β,β‐caroten‐8 ‐one‐3′‐acetate] was included in the study. The complete assignments of the 400 MHz 1H NMR spectra and of the 100.6 MHz 13C NMR spectra, including the stereochemistry, were possible by application of two‐dimensional 1H,1H chemical shift correlated spectroscopy (2D COSY), 1D and 2D total correlation spectroscopy (TOCSY, HOHAHA), rotating‐frame nuclear Overhauser spectroscopy (ROESY, CAMELSPIN) and 1H‐detected one‐bond (with and without 13C decoupling) and multiple‐bond 1H, 13C‐correlated 2D spectroscopy. The 9′‐trans to 9′‐cis stereomutation was unequivocally proved for 19′‐butanoyloxyfucoxanthin, mainly by 1D and 2D ROESY experiments; this is in contrast to a previously claimed 6′R → 6′S stereomutation in related allenic carotenoids.