1H NMR spectra (600 MHz) and structure of an industrial isobutylene-isoprene copolymer (butyl rubber)

Industrial samples of a copolymer of isobutylene with isoprene (butyl rubber) produced through cationic polymerization via the conventional slurry process (a Lewis acid (AlCl₃) as a coinitiator, methyl chloride as a diluent) have been studied with the use of proton magnetic resonance spectroscopy at an Larmor frequency of 600 MHz. Spectra were recorded for different types of deuterated solvents and concentrations of test solutions. The signals were processed via selective improving the resolution and signal-to-noise ratio. The use of these procedures, in combination with conformational representations, made it possible to increase the information content of the spectra.     

Towards the automatic analysis of NMR spectra: part 7. Assignment of 1H by employing both 1H and 1H/13C correlation spectra

A reliable method of automatically assigning one-dimensional proton spectra is described. The method relies on the alignment of the proton spectrum with an associated heteronuclear single-quantum coherence (HSQC) spectrum, transferring the stoichiometry and couplings to the HSQC. The HSQC spectrum is then assigned using a linear assignment procedure in which a fitness function incorporating (1)H chemical shifts, (1)H couplings and (13)C shifts are employed. The method uniquely employs a sequential procedure in which only correlations of like stoichiometry are assigned at the same time.     

60, 90 and 250 MHz 1H NMR spectra of sultams and sultones

The high-field ¹H NMR spectra of 1,3-propanesultams (2), 2,4-butanesultams (3) and 2,4-dimethyl-1,3-butadienesultams (6) are reported. Comparison of 2,3 and 6 with 1,3-propanesultone (1) and 2,4-dimethyl-1,3-butadienesultone (5) reveals that the paramagnetic shift induced by the NH group is smaller than that induced by oxygen. NMR spectra at lower temperature show coupling effects with the NH proton. A half-chair conformation was deduced for 2,4-butanesultam from coupling constants and from a conformational analysis based on the R values, but a chair-chair interconversion could not be detected in the temperature range between 210 and 330 K. An unambiguous assignment was carried out for the methyl signals in the spectrum of 5 by homodecoupling experiments.     

1H chemical shifts in NMR: Part 23, the effect of dimethyl sulphoxide versus chloroform solvent on 1H chemical shifts

The 1H chemical shifts of 124 compounds containing a variety of functional groups have been recorded in CDCl3 and DMSO-d6 (henceforth DMSO) solvents. The 1H solvent shift Delta delta = delta(DMSO) - delta(CDCl3) varies from -0.3 to +4.6 ppm. This solvent shift can be accurately predicted (rms error 0.05 ppm) using the charge model of alpha, beta, gamma and long-range contributions. The labile protons of alcohols, acids, amines and amides give both, the largest solvent shifts and the largest errors. The contributions for the various groups are tabulated and it is shown that for H.C.C.X gamma-effects (X = OH, NH, =O, NH.CO) there is a dihedral angle dependence of the gamma-effect. The group contributions are discussed in terms of the possible solvent-solute interactions. For protic hydrogens, hydrogen bonding is the dominant interaction, but for the remaining protons solvent anisotropy and electric field effects appear to be the major factors.     

Assignment of the NMR Parameters of the Branch-Point Trisaccharide of Ahylopectin Using 2-D NMR Spectroscopy at 500 MHz

Abstract

The proton and carbon nuclear magnetic resonance spectroscopic data for methyl 4-O-α-d-glucopyranosyl-[6-O-a-u-glucopyranosyl]-β-d-glucopyranoside (1), a model for the branch-point trisacch-aride of amylopectin, have been analysed using 2-D-heteronuclear correlated spectroscopy. Similar data are presented for the related disaccharide structures methyl β-d-maltopyranoside and β-d-isomal topyranoside.     

Assignment of relative configurations to acyclic diastereomeric carbinols with the lanthanide shift reagent Eu (fod)3 by 1H and 13C NMR

An assignment of relative configurations has been achieved for the diastereomeric racemates (1R2R,1S2S) and (1R2S,1S2R) of 3,3-dimethyl-1,2-diphenylbutan-1-ol through the comparative analysis of the respective chemical shifts induced by Eu(fod)₃ in the ¹H and ¹³C NMR spectra, and the corresponding conformational distribution.     

配合物Zn(II)-BPHA的^1H NMR谱

测定了各pD值下BPHA[BPHA是N,N'-bis(2-aminoethyl)-1,3-propanediaminehexaaceticacid的简称,中文名称为二胺乙基丙二胺六乙酸]和Zn^2^+-BPHA的^1HNMR谱。BPHA两端羧甲基上亚甲基质子的化学位移δ~a和中间羧甲基上亚甲基质子的化学位移δ~b随pD值交替变化。Zn^2^+-BPHA的^1HNMR谱有3种情况:pD<6,对应Zn(II)-H~2BPHA^4^-,有一特征尖峰,显示自由-NH^+(CH~2COO^-)~2残基存在;pD=6-9,对应Zn(II)-HBPHA^5^-,该峰消失,显示4个胺基全部配位;pD>9,对应Zn(II)-BPHA^6^-,该峰再次出现,1个N(CH~2COO^-)~2脱离配位体系。在3种形态的配合物中,Zn-N键都是非活性的,Zn-O键在后两种形态配合物中是非活性的。     

500 MHz 1H NMR studies on the configuration and conformation in the piezoelectric copolymer of vinylidene cyanide and vinyl acetate

The 500-MHz ¹H NMR spectrum of vinylidene cyanide-vinyl acetate copolymer, P(VDCN/VAc), provided detailed information concerning the configuration (ϵ-tacticity) and conformations. The ¹H NMR data also demonstrated that P(VDCN/VAc) is an equimolar and highly alternating copolymer without the regioirregular defects (complete head-to-tail arrangement), which is in good agreement with the previous C-13 NMR result. The calculated ϵ-isotacticity σ(ϵ) is equal to 0.5, suggesting that P(VDCN/VAc) is completely atactic. Due to this nonstereoregular structure, P(VDCN/VAc) in the bulk shows the amorphous phase by X-ray and DSC measurements. Making use of ¹H-homodecoupling, the splittings due to ϵ-tacticity as well as proton-proton spin coupling could be separately assigned. From the vicinal coupling constants, J(AX) and J(BX), obtained in methylene proton resonance, conformer populations around H(A)H(B)C-CH(X)-CH(A ‘)H(B’ ), were calculated. The conformation of P(VDCN/VAc) in DMF solution consists of only TG and TT, forming not a random coil structure but a helical structure with a large radius of curvature.     

13C and proton NMR spectra of 2(1H)pyrazinones

¹³C and proton NMR spectra data are given for eleven 2(1H)pyraziones. Assignments of chemical shifts were made by methods which included: deuterium exchange with certain protons of 3-alkyl substituents; change of chemical shifts of certain carbon atoms with change in pH; the use of long-range coupling constants for ¹³C to protons; and various correlations among assigned spectra.     

Diels-alder adducts of a spirocyclopentenotriazoloazodienophile. Assignment of their 1H and 13C NMR spectra

1-Phenyl-cyclopenteno[1,2-d]-1,2,3-rriazolo-5-spiro-4′-[perhydropyrazolino-3′,5′-dione] (5) afforded in situ, by oxidation with lead tetraacetate, the corresponding cyclopentenotriazolo-spiropyrazolodione 6 , which was trapped with dienes giving the hetero-Diels-Alder adducts 10–12 in good yields. The Diels-Alder reactions were examined on the basis of AM1 MO calculations. Total assignment of the ¹H- and ¹³C-nmr chemical shifts as well as the relative configuration of these adducts was accomplished with the help of 2D (¹H-¹H COSY, ¹H -¹ H NOESY, ¹H-¹³C XHCORR, ¹H-¹³C COLOC) and NOE difference spectroscopy. The structures of compounds 11a and 11b were also examined by molecular modeling.     

Dicondensed indolinobenzospiropyrans as precursors of thermo- and photochromic spiropyrans. Part II: Assignment of (1)H and (13)C NMR spectra

The (1)H and (13)C NMR spectra of dicondensed indolinobenzospiropyrans as precursors of thermo- and photochromic spiropyrans, DC1-DC5, were completely assigned. Especially, the (1)H assignment and coupling characteristics of the diastereotopic protons at the carbon-3 position of the benzopyran rings were achieved by conducting (1)H-(1)H COSY and nOe experiments. The dihedral angles (theta(1), theta(2) and theta(3)) calculated from the experimental values of the vicinal coupling constants ((3)J) of DC5 are in good agreement with the observed values in the solid state. All of the carbons in the DC dye molecules were investigated through a combination of heteronuclear 2D-shift correlation spectroscopy (HETCOR) and DEPT135.     

Assignment of the 1H and 13C NMR of tocotrienols

Vitamin E is a family of chromanols that vary by the degree of methylation of the chroman ring as well as the nature of the hydrophobic side chain at C2 that serves to anchor these lipids in biological membranes. The tocopherols contain saturated side chains, whereas the tocotrienols contain three sites of unsaturation and are derived from geranylgeranyl diphosphate. A growing interest in the unique biological activities of the tocotrienols has led us to begin syntheses of isotopically substituted forms and other derivatives that will be useful for probing the metabolism and membrane behavior of the tocotrienols. In order to be certain of our ability to selectively modify sites on the parent molecules it was necessary to make as complete an assignment of the 1H and 13C NMR as possible. Herein we report multidimensional NMR data (HSQC, COSY, ADEQUATE(1,1), C--H HMBC, and NOESY) that have allowed us to assign the identity of almost all the resonances for alpha-, beta-, gamma-, and delta-tocotrienol.     

NMR experiments for the analysis of mixtures: beyond 1D 1H spectra

State-of-the-art technologies and methodologies in NMR spectroscopy make it possible to obtain very informative and high-quality spectra in much less experimental time than classical methods by making better choices of NMR pulse sequences and acquisition parameters. This review presents some recent NMR methods allowing rapid identification, assignment and structural characterization of the components in mixtures. The relative merits of the different NMR pulse sequences are briefly discussed and recommendations are made for the preferred choice of sequences to obtain rapidly artifact-free data. This review covers diffusion experiments (DOSY), HSQC and HMBC experiments, ultra-resolved 2D spectra exploiting the property of aliasing and NOESY/ROESY experiments. It will be in particular shown that selective 1D NOESY/ROESY sequences can be more informative and reach higher resolution in less experimental time than the corresponding 2D sequences.     

Assignment of proton NMR spectra and conformational analysis by two-dimensional heteronuclear relayed correlation NMR spectroscopy

The method of two-dimensional heteronuclear relayed correlation spectroscopy was used to establish the assignment of the severely overcrowded part of the proton spectrum of menthol by relating it to the previously assigned carbon spectrum. Extrapolation of the signal-to-noise ratio obtained with overnight data accumulation on a 10 mM solution suggests that this experiment should be feasible on as little as 10 mg of a moderate-sized organic compound.     

The 1H NMR spectra of 8-quinolinolato complexes of Mn(III)

¹H NMR spectra are reported for tris(8-quinolinolato)manganese(III), tris(2-methyl-8-quinolinolato)manganese(III) and mixtures of tris(acetylacetonato)manganese(III) and tris(8-quinolinolato)manganese(III). In the latter case, mixed complexes are formed in equilibrium, with only one of the three possible isomers of acetylacetonato bis(8-quinolinolato)manganese(III) being present in detectable amounts. The spectra were assigned making extensive use of selective deuteriation.     

Polarographic behaviour of some organotin(IV) compounds in dimethyl sulphoxide

The differential pulse polarographic behaviour in dimethyl sulphoxide (DMSO) of 14 organotin(IV) compounds having the general formula R₃SnX (R = Me, Ph; X^? = NCS^?, N₃^?, N₃^?, NO₃^?, OH^?, NCO^? and OAc^?) and ⁿBu₃SnCl and ⁿBu₂SnCl₂ has been studied. The peak potential was found to depend markedly on the organic group and to a lesser extent on the nature of the anion X. The phenyltin compounds were reduced at lower potentials than the corresponding methyltin compounds. The data obtained could be used for trace determination of these compounds. Linear calibration curves were obtained over the concentration range of 2.8 × 10^?4 to 1.9 × 10^?6 mol dm^?3.     

Conformational analysis of 2,2'-bithiophene: a (1)H liquid crystal NMR study using the (13)C satellite spectra

We have obtained a very large data set of spectral parameters from the analysis of (1)H NMR and (13)C satellite spectra of 2,2'-bithiophene dissolved in anisotropic, partially orienting mesophases. In particular, this parameter set includes 33 dipolar couplings, which are directly related to the interatomic distances, the dihedral angle phi between the two thiophenic rings, and the anisotropic solute-solvent interaction potential. This allows an exhaustive investigation of the conformational equilibrium of 2,2'-bithiophene in a liquidlike phase. Comparison with the predictions of high-level theoretical calculations for the isolated molecule provides evidence of a strong flattening as well as the sharpening effect of the medium on the conformer population. The approximations needed to apply vibrational corrections to flexible molecules are discussed in detail and some general conclusions concerning their effect on structure and conformational equilibria are proposed.     

Assignment of finely resolved 13C NMR spectra of poly(vinyl acetate)

¹³C NMR spectra of two poly(vinyl acetate)s (PVAC) with different tacticities (r‐diad, 0.54 and 0.57) were measured, and their peak intensities were compared with the calculated ones. The methine carbon signals were assigned with pentads in the order of mmmm, mmmr + rmmr, rmrr + mmrr, rrrr, mmrm, rmrm, mrrr, mrrm from low field. The methylene carbon signals were assigned with tetrads (partly with hexads) as rmr, rrr(mrrrm, mrrrr, rrrrr), mmr + mrr, mrm and mmm from low field. Some assignments are different from those previously reported. The methyl carbon signals showed splittings which were partly assigned.