1,6-六亚甲基二异氰酸酯自聚产物的结构表征

用IR与NMR表征了用醋酸钾为催化剂时 1,6 六亚甲基二异氰酸酯 (HDI)自聚产物的结构 .结果表明 ,自聚主产物是三聚体异氰脲酸酯 ,主要含有三聚体异氰脲基、异氰酸根 ,同时含有由杂质带来的微量氨基甲酸酯、脲基甲酸酯基、取代脲基、缩二脲基 .一维核磁谱及二维化学位移相关谱分辨出 7种羰基 ,一种NCO基 ,确定了氮上 8种不同取代结构的分子链连接情况 .通过建立理论模型 ,定量地描述了自聚产物的结构 .     

Solution structure of the palladium(II) complex of 1,4,7,10-tetrathiacyclododec-2-ene-2,3-dicarbonitrile

The solution structure of the Pd(II) complex of mn-12-S4 was studied in detail by NMR spectroscopy. The stoichiometry of the complex was determined by 1H NMR titration experiments. 3J(H,H) coupling constants were extracted from the 2D J-resolved NMR spectrum of the complex providing information concerning the S-C-C-S torsional angles. Further conclusions about the conformation of [Pd(mn-12-S4)](BF4)2 were drawn from experimental NOEs. The results of the NMR study were corroborated by molecular modelling.     

2D NMR studies of acrylonitrile-methyl acrylate copolymers

The microstructure of acrylonitrile-methyl acrylate copolymers prepared by the solution polymerization using 2,2′-azobisisobutyronitrile (AIBN) as free radical initiator was investigated by two-dimensional NMR techniques. 2D-heteronuclear single quantum correlation (HSQC) and the total correlation spectroscopy (TOCSY) have been utilized to resolve the complex ¹H NMR spectrum and to establish the compositional and configurational sequences of acrylonitrile-methyl acrylate copolymers. 2D HSQC and TOCSY showed compositional and configurational sensitivity of methine protons of A and M units upto the triad level. Heteronuclear multiple-bond correlation (HMBC) spectroscopy has been used to study carbon (carbonyl/nitrile)-proton coupling. The carbonyl and nitrile carbons showed compositional sensitivity upto the triad level. The values of reactivity ratios were determined by Kelen-Tudos (KT) and non-linear error in variable method (RREVM).     

氧氟沙星的核磁共振波谱性质研究

结合1H, 13C NMR, DEPT, COSY, HSQC, HMBC谱和碳氟偶合裂分行为, 对酸性及碱性溶液中氧氟沙星(Ofloxacin, OFL)的1H和13C谱分别进行归属, 研究了哌嗪环亚甲基构成的AA'BB'复杂自旋体系中各H的化学位移. 发现噁嗪环上的甲基处于直立键; 5H在酸性溶液中化学位移移向低场, 这可能与形成C—H…O弱氢键有关; 在碱性溶液中, OFL的羧基变为羧酸根, 造成羧基和羰基周围碳原子上π电子重新分布, 导致相应C的化学位移和碳氟偶合常数发生明显变化.     

Scalar Coupling between the 15N Centres in Methylated 1,8‐Diaminonaphthalenes and 1,6‐Diazacyclodecane: To What Extent is 2HJNN a Reliable Indicator of N?N Distance?

The scalar couplings between hydrogen bonded nitrogen centres ((2H)J(NN)) in the free-base and protonated forms of the complete series of [(15)N(2)]-N-methylated 1,8-diamino naphthalenes in [D(7)]DMF solution have been determined, either directly (15N[1H] NMR), or, indirectly (13C[1H] NMR and simulation of the X part of the ABX spectrum (X=13C, A,B=15N)). Additionally, the (2H)J(NN) value in the HBF(4) salt of [(15)N(2)]-1,6-dimethyl-1,6-diazacyclodecane was determined, indirectly by 13C[(1H] NMR spectroscopy. As confirmed by DFT calculations and by reference to CSD, the rigid nature of the naphthalene scaffold results in rather low deviations in N,N distance or H-N,N angle within each series, apart from the free base of the permethylated compound (proton sponge) where the naphthalene ring is severely distorted to relieve strain. Despite such restrictions, the (2H)J(NN) values increase smoothly from 1.5 to 8.5 Hz in the protonated series as the degree of methylation increases. The effect in the free-base forms is much less pronounced (2.9 to 3.7 Hz) with no scalar N,N coupling detected in the permethylated compound (proton sponge) due to the lack of hydrogen bond between the N,N centres. Neither the pK(a) nor the N-N distance in the protonated forms correlates with (2H)J(NN). However, the sum of the (13)C NMR shifts of the naphthalene ring C(1,8) carbons which are attached directly to the nitrogen centres correlates linearly with (2H)J(NN) and with the degree of methylation. The gas-phase computed (2H)J(NN) is almost constant throughout the homologous series, and close to the experimental value for the tetramethylated ion. However, the computed coupling constant is attenuated in structures involving microsolvation of each N-H unit, and the trend then matches experiment. These experimental and computational observations suggest that Fermi contact between the two N centres is decreased upon formation of strong charge-dispersing intermolecular hydrogen bonds of the free N-H groups with the solvent.     

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.     

Conformational evaluation and detailed 1H and 13C NMR assignments of eremophilanolides

Extensive application of 1D and 2D NMR methodology, combined with molecular modeling, allowed the complete 1H and 13C NMR assignments of eremophilanolides from Senecio toluccanus. Comparison of the experimental 1H, 1H coupling constant values with those generated employing a generalized Karplus-type relationship, using dihedral angles extracted from MMX and DFT calculations, revealed that the epoxidized eremophilanolides 1 and 2 show conformational rigidity at room temperature, whereas molecules 3-6, containing an isolated double bond, are conformationally mobile.     

Different types of hydrogen bonds in 2-substituted pyrroles and 1-vinyl pyrroles as monitored by (1)H, (13)C and (15)N NMR spectroscopy and ab initio calculations

According to the (1)H, (13)C and (15)N NMR spectroscopic data and ab initio calculations, the strong N--H...O intramolecular hydrogen bond in the Z-isomers of 2-(2-acylethenyl)pyrroles causes the decrease in the absolute size of the (1)J(N,H) coupling constant by 2 Hz in CDCl(3) and by 4.5 Hz in DMSO-d(6), the deshielding of the proton and nitrogen by 5-6 and 15 ppm, respectively, and the lengthening of the N--H link by 0.025 A. The N--H...N intramolecular hydrogen bond in the 2(2'-pyridyl)pyrrole leads to the increase of the (1)J(N,H) coupling constant by 3 Hz, the deshielding of the proton by 1.5 ppm and the lengthening of the N--H link by 0.004 A. The C--H...N intramolecular hydrogen bond in the 1-vinyl-2-(2'-pyridyl)-pyrrole results in the increase of the (1)J(C,H) coupling constant by 5 Hz, the deshielding of the proton by 1 ppm and the shortening of the C--H link by 0.003 A. Different behavior of the coupling constants and length of the covalent links under the hydrogen bond influence originate from the different nature of the hydrogen bonding (predominantly covalent or electrostatic), which depends in turn on the geometry of the hydrogen bridge. The Fermi-contact mechanism only is responsible for the increase of the coupling constant in the case of the predominantly electrostatic hydrogen bonding, whereas both Fermi-contact and paramagnetic spin-orbital mechanisms bring about the decrease of coupling constant in the case of the predominantly covalent hydrogen bonding.     

Comparative analysis of hydrogen bonding with participation of the nitrogen, oxygen and sulfur atoms in the 2(2'-heteroaryl)pyrroles and their trifluoroacetyl derivatives based on the 1H, 13C, 15N spectroscopy and DFT calculations

The N-H...X (X = N,O,S) intramolecular hydrogen bond in the series of 2(2'-heteroaryl)pyrroles and their trifluoroacetyl derivatives is examined by the (1)H, (13)C, (15)N spectroscopy and density functional theory (DFT) calculations. The influence of the hydrogen bond on coupling and shielding constants is considered. It is shown that the N-H...N intramolecular hydrogen bond causes a larger increase in the absolute size of the (1)J(N,H) coupling constant and a larger deshielding of the bridge proton than the N-H...O hydrogen bond. The effect of the N-H...S interaction on the (1)J(N,H) coupling constant and the shielding of the bridge proton is small. The NMR parameter changes in the series of the 2(2'-heteroaryl)pyrroles due to N-H...X hydrogen bond and the series of the 1-vinyl-2-(2'-heteroaryl)-pyrroles due to C-H...X hydrogen bond have the same order. The proximity of the nitrogen, oxygen or sulfur lone pair to the F...H hydrogen bridge quenches the trans-hydrogen bond spin-spin couplings (1h)J(F,H-1) and (2h)J(F,N).     

Hartree-Fock, Møller-Plesset calculations and dynamic NMR study of 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one

The experimental (1)H, (13)C NMR spectra of 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one were recorded in CDCl(3) at temperature range 213-323 K. The variable temperature spectra revealed a dynamic NMR effect which is attributed to restricted rotation around the C=C double bond. Fast exchange processes of deuterium atoms between CDCl(3) and 3,3-dimethoxy-1-(imidazolidin-2-ylidene)propan-2-one or fast exchange of proton between nitrogen and oxygen atoms of carbonyl group is also revealed by broadening of N-H (singlet) proton NMR signals. Proton and carbon theoretical chemical shifts of the title molecule were calculated by using RHF and MP2-GIAO levels and different basis sets in gas phase at 298 K. The calculated proton chemical shifts show that the experimental values have no agreement with theoretical values, but for carbon chemical shifts a good agreement achieved by using RHF with 6-31G basis set and MP2/3-21G, 6-31G basis sets. Discrepancies are attributed to either the limitations of calculating program, because the change of the structure while rotation are not considered. The results showed that to select of basis set has more important rule, because RHF-GIAO level calculation with 6-31G basis set in gas phase can excellently reproduce the (13)C NMR spectrum. Moreover, MP2/3-21G, 6-31G calculation has not significant influence on (13)C NMR chemical shifts with respect to RHF-6-31G.     

GIAO,DFT, AIM and NBO analysis of the N?H···O intramolecular hydrogen‐bond influence on the 1J(N,H) coupling constant in push–pull diaminoenones

In the series of diaminoenones, large high‐frequency shifts of the ¹H NMR of the N? H group in the cis‐position relative to the carbonyl group suggests strong N? H···O intramolecular hydrogen bonding comprising a six‐membered chelate ring. The N? H···O hydrogen bond causes an increase of the ¹J(N,H) coupling constant by 2–4 Hz and high‐frequency shift of the ¹⁵N signal by 9–10 ppm despite of the lengthening of the relevant N? H bond. These experimental trends are substantiated by gauge‐independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3‐bis(isopropylamino)‐1‐(aryl)prop‐2‐en‐1‐one (12) for conformations with the Z‐ and E‐orientations of the carbonyl group relative to the N? H group. The effects of the N? H···O hydrogen‐bond on the NMR parameters are analyzed with the atoms‐in‐molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the N? H···O hydrogen bond as compared with that of 1,1‐di(pyrrol‐2‐yl)‐2‐formylethene (13) where N? H···O hydrogen bridge establishes a seven‐membered chelate ring, and the corresponding ¹J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) →σ*_{N? H} hyperconjugative interaction is weakened on going from the six‐membered chelate ring to the seven‐membered one due to a more bent hydrogen bond in the former case. A dominating effect of the N? H bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the ¹J(N,H) value as a consequence of the N? H···O hydrogen bonding in the studied diaminoenones. Copyright © 2010 John Wiley & Sons, Ltd.     

1H NMR studies of maltose,maltoheptaose, alpha-, beta-, and gamma-cyclodextrins,and complexes in aqueous solutions with hydroxy protons as structural probes

The (1)H NMR chemical shifts, coupling constants, temperature coefficients, and exchange rates have been measured for the hydroxy protons of aqueous solutions of alpha-, beta-, and gamma-cyclodextrins, maltose, and maltoheptaose. In cyclodextrins (CDs), the high chemical shift of the O(3)H signal and its small (3)J(OH,CH) value suggest that O(3)H is involved in a hydrogen bond. The small temperature coefficients and rate of exchange values of O(2)H and O(3)H confirm the involvement of O(3)H in hydrogen bonding and indicate that O(2)H is the hydrogen bond partner. In maltose, two distinct NMR signals with two different vicinal coupling constants are found for O(2')H. A cross-peak in the ROESY spectrum indicates chemical exchange between the O(2')H and O(3)H protons. The existence of two distinct NMR signals with different J values for O(2')H shows the influence of anomeric configuration on the O(2')H-O(3)H interaction. The effect of complexation with methyl benzoate, adamantane-1-carboxylic acid, adamantane-1-ol, and l- and d-tryptophane on the NMR spectra of the hydroxy protons of alpha-, beta-, and gamma-cyclodextrins and of maltose has been investigated. No significant spectral changes were observed upon addition of methyl benzoate and adamantane-1-carboxylic acid. The addition of adamantane-1-ol resulted in an upfield shift and a strong broadening of the O(2)H signal from alpha-CD, and a small temperature coefficient was measured upon complexation. The O(2)H and O(3)H signals in beta-CD were broadened and shifted downfield upon addition of l- and d-tryptophane.     

Ab initio EOM-CCSD spin-spin coupling constants for hydrogen-bonded formamide complexes: bridging complexes with NH3, (NH3)2, H2O, (H2O)2, FH, and (FH)2

EOM-CCSD spin-spin coupling constants across hydrogen bonds have been computed for complexes in which NH3, H2O, and FH molecules and their hydrogen-bonded dimers form bridging complexes in the amide region of formamide. The formamide one-bond N-H coupling constant [(1)J(N-H)] across N-H...X hydrogen bonds increases in absolute value upon complexation. The signs of the one-bond coupling constants (1h)J(H-X) indicate that these complexes are stabilized by traditional hydrogen bonds. The two-bond coupling constants for hydrogen bonds with N-H as the donor [(2h)J(N-X)] and the carbonyl oxygen as the acceptor [(2h)J(X-O)] increase in absolute value in the formamide/dimer relative to the corresponding formamide/monomer complex as the hydrogen bonds acquire increased proton-shared character. The largest changes in coupling constants are found for complexes of formamide with FH and (FH)2, suggesting that bridging FH monomers and dimers in particular could be useful NMR spectroscopic probes of amide hydrogen bonding.     

J(F,H), J(C,H) and J(H,H) couplings involving the individual methyl group protons in 1,2,3,4-tetrachloro-5,6,7,8-tetrafluoro-9-methyltriptycene. Evidence of blue-shifting hydrogen bond

1,2,3,4-tetrachloro-5,6,7,8-tetrafluoro-9-methyltriptycene was studied in NMR spectra at low temperatures where the methyl group dynamics is frozen. Values of 5J(19F,1H), 1J(13C,1H), and 2J(1H,1H) for the individual methyl protons were measured. They are in a fair agreement with the corresponding theoretical values calculated at a density functional theory (DFT) level. The 5J(19F,1H) couplings involve the peri-F nucleus and occur via the 'through space' mechanism. Both the natural bond orbital analysis (at a HF level) and the observed pattern of 1J(13C,1H) coupling values corroborate occurrence in this molecule of intramolecular, blue-shifting hydrogen bonds engaging the methyl hydrogens. The 'through space' 5J(19F,1H) couplings may indicate the routes of electron density transfers that escape detection by the natural bond analysis. A consideration of these effects can enrich the chemical intuition involving this specific sort of H-bonds.     

Complete basis set B3LYP NMR calculations of CDCl3 solvent's water fine spectral details

The assignment of singlet at 1.55 ppm and the 1:1:1 triplet at 1.519 ppm to H(2)O and HOD in the 400 MHz (1)H NMR spectrum of CDCl(3) solvent were supported by complete basis set (CBS) GIAO-B3LYP calculated chemical shift and the CBS B3LYP estimated (2)J(D,H) spin-spin coupling constant (SSCC). The CBS fitting of B3LYP/cc-pCVxZ and B3LYP/pcJ-n predicted SSCC values, the accurate value of (2)J(D,H) = -1.082 +/- 0.030 Hz of HOD in chloroform-d(1) and the H/D isotopic shift of 0.0307(1) ppm were reported for the first time. The agreement between CBS B3LYP predicted chemical shift, spin-spin values and experiment was good.     

Characterization of Doubly Ionic Hydrogen Bonds in Protic Ionic Liquids by NMR Deuteron Quadrupole Coupling Constants: Differences to H‐bonds in Amides,Peptides, and Proteins

We present the first deuteron quadrupole coupling constants (DQCCs) for selected protic ionic liquids (PILs) measured by solid‐state NMR spectroscopy. The experimental data are supported by dispersion‐corrected density functional theory (DFT‐D3) calculations and molecular dynamics (MD) simulations. The DQCCs of the N−D bond in the triethylammonium cations are the lowest reported for deuterons in PILs, indicating strong hydrogen bonds between ions. The NMR coupling parameters are compared to those in amides, peptides, and proteins. The DQCCs show characteristic behavior with increasing interaction strength of the counterion and variation of the H‐bond motifs. We report the similar presence of the quadrupolar splitting pattern and the narrow liquid line in the NMR spectra over large temperature ranges, indicating the heterogeneous nature of PILs.     

用核磁共振技术研究氢键的键合方式

为了了解怎样利用核磁共振技术研究氢键的键合方式,本文以联酰胺衍生物为例,分别运用变温核磁共振氢谱和变浓度核磁共振氢谱分析了羰基(CO)与氨基(H—N)之间形成氢键的形式。结果表明,本文举例中联酰胺基团中的CO与H—N以分子间氢键形式存在。     

1H-1H scalar coupling across two stacked aromatic rings: DFT calculations and experimental proof

1H-1H scalar coupling across two stacked (parallel and eclipsed) aromatic rings has been revealed through the 1D and 2D 1H NMR analysis of a [2,2]paracyclophane and rationalized by means of density functional theory (DFT) calculation of the J values.     

Variation in protein C(alpha)-related one-bond J couplings

Four types of polypeptide (1)J(C alpha X) couplings are examined, involving the main-chain carbon C(alpha) and either of four possible substituents. A total 3105 values of (1)J(C alpha H alpha), (1)J(C alpha C beta), (1)J(C alpha C'), and (1)J(C alpha N') were collected from six proteins, averaging 143.4 +/- 3.3, 34.9 +/- 2.5, 52.6 +/- 0.9, and 10.7 +/- 1.2 Hz, respectively. Analysis of variances (ANOVA) reveals a variety of factors impacting on (1)J and ranks their relative statistical significance and importance to biomolecular NMR structure refinement. Accordingly, the spread in the (1)J values is attributed, in equal proportions, to amino-acid specific substituent patterns and to polypeptide-chain geometry, specifically torsions phi, psi, and chi(1) circumjacent to C(alpha). The (1)J coupling constants correlate with protein secondary structure. For alpha-helical phi, psi combinations, (1)J(C alpha H alpha) is elevated by more than one standard deviation (147.8 Hz), while both (1)J(C alpha N') and (1)J(C alpha C beta) fall short of their grand means (9.5 and 33.7 Hz). Rare positive phi torsion angles in proteins exhibit concomitant small (1)J(C alpha H alpha) and (1)J(C alpha N') (138.4 and 9.6 Hz) and large (1)J(C alpha C beta) (39.9 Hz) values. The (1)J(C alpha N') coupling varies monotonously over the phi torsion range typical of beta-sheet secondary structure and is largest (13.3 Hz) for phi around -160 degrees. All four coupling types depend on psi and thus help determine a torsion that is notoriously difficult to assess by traditional approaches using (3)J. Influences on (1)J stemming from protein secondary structure and other factors, such as amino-acid composition, are largely independent.     

Stereochemical analysis of the 3α‐ and 3β‐hydroxy metabolites of tibolone through NMR and quantum‐chemical investigations. An experimental test of GIAO calculations

The configuration at C‐3 of the 3α‐ and 3β‐hydroxy metabolites of tibolone was studied by extensive application of one‐ and two‐dimensional ¹H and ¹³C NMR spectroscopy combined with molecular modeling performed at the B3LYP/6–31G(d) level. Using HF and DFT GIAO methods, shielding tensors of the two molecules were computed; comparison of the calculated NMR chemical shifts with the experimental values revealed that the density functional methods produced the best results for assigning proton and carbon resonances. Although steroids are relatively large molecules, the present approach appears accurate enough to allow the determination of relative configurations by using calculated ¹³C resonances; the chemical shift of pairs of geminal α/β hydrogen atoms can also be established by using calculated ¹H resonances. Copyright © 2002 John Wiley & Sons, Ltd.