Reactivity of the Hydroxy Groups in Melezitose and Their Selective Protection

The reactivity of melezitose hydroxy groups was studied by tritylation in pyridine with subsequent acetylation. After partial detritylation of the products, acetyl group transfer from position 4 to 6 was observed. The structure of the prepared melezitose derivatives was established on the basis of their IR, ¹H, ¹³C, and ¹H-¹H COSY NMR, and mass spectra (fast atom bombardment), as well as from the results of model calculations performed with the aid of SGI Indigo Molecule-Pattern-Work-Station software package (Biosym) where the potential energy function was approximated with the CVFF potential. The reactivity of primary hydroxy groups in melezitose was found to decrease in the following order: 6' > 6 6' > 1'.     

The assignment of diastereotopic menthyl groups by two-dimensional NMR

The ¹³C and ¹H NMR spectra of (–)-bis[1R, 3 R, 4S]menthylphosphine (1) are assigned by two-dimensional double quantum NMR and ¹³C? ¹H shift correlation diagrams. The variable temperature spectra of 1 indicate hindered rotation about the P? C bonds.     

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

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

High-resolution NMR spectra of fluorene and its derivatives: VI—1-methylfluorene,truxene and decacyclene

The overlapping spin systems in the 220 MHz ¹H spectra of 1-methylfluorene (1) in carbon disulphide and deuteriated chloroform solutions have been analysed separately and refined by LAOCOON with the aid of methyl- and methylene-decoupled spectra. Ortho-coupling constants in the 6-membered rings are similar to each other and to those in fluorene (4). Solvent and concentration shifts suggest loose pairing of solute molecules. 220 MHz ¹H spectra of α-truxene (2) in carbon tetrachloride and deuteriated nitrobenzene, 220 MHz ¹H spectra of decacyclene (3) in carbon tetrachloride, and 90 MHz FT ¹H spectra of 3 in deuteriated chloroform show steric deshielding; the solvent dependence of shifts also suggests solute pairing in 2. Shifts in ¹H decoupled 22.6 MHz ¹³C spectra of 2 in deuteriated chloroform were assigned with the aid of Cr(acac)₃ relaxation agent.     

Carbon-13 NMR study of some isomeric n-nitroindazole derivatives

The ¹³C NMR spectra of 1,5- and 2,x-dinitroindazoles “x=4-7” and 3-bromo-1,x-dinitroindazoles are recorded and discussed. The data on he 2,x-dinitroindazoles confirm our previous structurea assignment based on ¹H NMR spectroscopy. The ¹³C NMR spectra established that in the novel 3-bromo-1,x-dinitroindazoles the N-nitro group is attached at N-1.     

1H and 13C NMR studies on 1,3,2-dioxarsolanes

The ¹H and ¹³C NMR spectra of a series of 1,3,2-dioxarsolanes have been obtained at 2.1 T and some at 9.4 T. The chemical shifts and spin-spin coupling constants have been obtained from complete spectral analyses of the ¹H and proton-coupled ¹³C spectra. The spectral data are interpreted on the basis of two rapidly interconverting half-chair conformers with a pseudoaxial substituent at arsenic. Unique assignment of syn/anti or cis/trans geometries have been made from ¹H or ¹³C NMR spectroscopy alone. The syn and trans isomers of the 4-methyl- and 4,5-dimethyl-1,3,2-dioxarsolanes, respectively, appear to be conformationally biased towards the forms with pseudoequatorial methyl groups. The general trends in the geminal and vicinal ¹H? ¹H and ¹³C? ¹H coupling constants are interpreted in terms of stereospecific, electronegativity and lone-pair effects of the oxygen heteroatoms and conformational factors. The NMR data on the 1,3,2-dioxarsolanes are discussed with reference to related 1,3-dithoxa- and 1,3-dithia- five-membered rings with As, P, S or C at the 2-position.     

Synthesis and spectroscopic characterizations of both 4b,5-dihydro-4b-methyl-11H-isoindolo[2,1-a]benzimidazol-11-ones and 2,3,3a,4-tetrahydro-3a-methyl-1H-pyrrolo[1,2-a]benzimidazol-1-ones

The complete assignment of the ¹H and ¹³C nmr spectra of some derivatives of both 4b,5-dihydro-4b-methyl-11H-isoindolo[2,1-a]benzimidazol-11-one I and 2,3,3a,4-tetrahydro-3a-methyl-1H-pyrrolo[1,2-a]-benzimidazol-1-one II was herein reported by the combined use of one and two-dimensional nmr techniques. Eight compounds, three of which are novel, 2a, 3, 6 , were thus prepared. Their uv and ir spectra were also obtained. In addition, the mass spectra of compounds 1, 2a, 2b, 3 and 6 are reported.     

1H and 13C NMR of PMMA macromonomers and oligomers - end groups and tacticity

¹H NMR and ¹³C NMR have been used to study the end groups and tacticity in PMMA macromonomers and oligomers. These macromonomers are terminated almost exclusively in one vinylidene group per chain. The end group signals from the macromonomers are identified in both the ¹³C and ¹H NMR spectra. The spectra of the purified oligomers (n = 1-4) were used to aid in assignment. The macromonomers are predominantly syndiotactic, and the tacticity measured is consistent with Bernoullian statistics. The tetramer is a mixture of r and m isomers in a 4:1 ratio. It is shown that T₁ experiments can provide a useful method of distinguishing resonances due to low molecular weight impurities from those due to stereochemical or isomeric effects in macromonomers. The absence of internal double bonds was confirmed by isomerizing the vinylidene group of several oligomers and of the macromonomer, and verifying the absence of the isomerized signals in the NMR spectra of the original materials.     

Fluoroazoles. II. Synthesis and 1H and 19F Nmr spectra of 2-, 4-, and 5-Fluoro-1-methylimidazole

The three possible ring-monofluorinated N-methylimidazoles have been prepared by photochemical irradiation of the corresponding diazonium tetrafluoroborates. 5-Fluoro-1-methyl-imidazole was also obtained by methylation of 1-acetyl-4-fluoroimidazole. The ¹H and ¹⁹F nmr spectra of these N-methylated fluoroazoles are compared, and the predominance of one tautomeric form in 4(5)-fluoroimidazole is discussed.     

Identification of some isomeric 3,5-unsymmetrically substituted 1-aroyl-pyrazole derivatives by NMR spectroscopy

The ¹H and ¹³C nmr chemical shifts are used for the structural assignment of isomeric 1-aroyl-4,5-dihydro-5-hydroxy-4,4-dimethyl-1H-pyrazoles 1 unsymmetrically substituted with phenyl or methyl in the 3,5-positions of the pyrazole ring. The ¹H nmr spectra of 1-aroyl- or 1-acetyl-4-methyl-1H-pyrazoles 2 are useful in structure elucidation of unsymmetrically 3- or 5-methyl substituted derivatives.     

Studies of C. I. Acid Red 186 and Metal Complexes with Uo++2, Ce3+ and Th6+ Ions

The electronic absorption spectra of C. I. Acid Red 186 are studied in solution of different pH. The pK values of the acid-base equilibria set are determined and commented upon. The complexes of UO⁺⁺₂, Ce³⁺ and Th⁴⁺ ions are investigated by some spectroscopic techniques and potentiometric titration. The formation of 1:1, 1:2 and 1:2 complexes (M:L) with UO₂⁺⁺, Ce³⁺ and Th⁴⁺ respectively is confirmed and their conditional stability constants are determined. The solid complexes are prepared and analysed for their metal content, their ir spectra are disussed in comparison to that of the ligand to establish the bonding between the ligand and metal ions.     

Synthesis and characterization of 7, 16‐bis(phenylazo)tetraaza[14]annulenes

The diazo coupling reaction between a tetraaza[14]annulene ( 1 ) and a series of 4‐substituted phenyl‐diazonium tetrafluoroborates yielded the corresponding 7, 16‐disubstituted products. Mass spectra indicate the presence of molecular ion peaks that substantiate the 7,16‐disubstituted products ( 4 ); the lack of olefinic proton signals corresponding to the 7,16‐ position in the ¹H nmr spectra of 4 also show that diazo coupling has taken place. Analysis of signals corresponding to the methyl groups of 4 in their ¹H and ¹³C nmr spectra indicate that the imine‐bis‐hydrazone form is present for compounds that do not contain p‐methoxyphenyl groups. However, analysis of methyl signals in the nmr specta of compounds 4 containing p‐methoxyphenyl groups show that the bis‐azo form and the imine‐bis‐hydrazone form are present through tautomerism. Complexation with nickel(II) ion induces the formation of the bis‐ azo structure.     

Conformational analysis of benzoannulated nine-membered rings. Part 3. 1,4,5,7-Tetrahydro-3H-2,6-benzodiselenine and its 4-spiro derivatives

The ¹H and ¹³C nmr spectra of 1,4,5,7-tetrahydro-3H-2,6-benzodiselenine (1) and three 4-spiro derivatives 2–4 as well as the ⁷⁷Se nmr spectra of 2 have been recorded at different temperatures in order to investigate their conformational behavior. It was found that in analogy to corresponding dithionins the molecules adopt a chiral ground state conformation (Figure 2), and coalescence effects are due to racemization.     

1H and 13C nuclear magnetic resonance study of (D3)-trishomocuban-4-ol and (D3)-trishomocubanone

The complete assignments of the ¹H and ¹³C NMR spectra for (D₃)-trishomocuban-4-ol (3) and (D₃)-trishomocubanone (4) are reported. The difference between the ¹H and ¹³C chemical shifts of 3 and 4 and those of the hydrocarbon (D₃)-trishomocubane, and the substituent effect of the hydroxy group, can be adequately explained by the unique stereochemistry of these compounds.     

Chemoselective synthesis and spectral studies of N-thiocyanatoacetyl derivatives of 3-alkyl-2,6-diarylpiperidin-4-ones

A series of N–thiocyanatoacetyl derivatives of 3–alkyl–2,6–diarylpiperidin–4–ones has been synthesized by the reaction between the N–chloroacetyl derivatives of the respective piperidin–4–ones and the ambident thiocyanate nucleophile. The synthesized compounds have been characterized through FT–IR, ¹H, ¹³C, ¹H–¹H COSY, ¹H–¹³C COSY and NOESY spectra. The spectral data reveal the conformational priority of the six-membered heterocyclic ring.     

Etude des Signes des Constantes de Couplage 3J(P?X?C?H) et 4J(F?P?X?C?H) dans les Diaza-, Dioxa- et Dithiaphospholanes Fluores

The NMR spectra of the trivalent fluorophospholanes ( 1, 2, 3 ) have been analysed at length. The absolute signs of the ³J(P? H) and ⁴J(F? H) coupling constants have been referred to the known negative sign of the ¹J(P? F) coupling constant from selective heteronuclear double resonance experiments. The ³J(P? O? C? H) and ³J(P? N? C? H) coupling are positive. The weak values observed for ³J(P? S? C? H) have opposite signs, the larger being positive. All the ⁴J(F? P? X? C? H) coupling constants are positive showing a lack of stereospecificity.     

The assignment of the 1H and the 13C NMR chemical shifts of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam

The assignment of the signals in the ¹³C and ¹H NMR spectra of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam is difficult for the signal pairs C-2 and C-4, C-1 and C-3, (C-1)? H, (C-2)? CH₃ and (C-4)? CH₃. The ¹³C NMR spectrum recorded under gated decoupling conditions provide long-range couplings which make possible an unambiguous assignment of the ¹³C NMR signal pairs. Application of the ¹H CW off-resonance decoupling technique in recording the ¹³C NMR spectra enables the assignment information from the ¹³C NMR spectrum to be transferred to the ¹H NMR spectrum.     

Carbon-13 and proton magnetic resonance spectra of 2,4-disubstituted 3,3-diphenyltetrahydrofurans derived from isomethadone and isomethadol

Proton and carbon-13 nmr spectra for cis- and trans-2-ethyl-3,3-diphenyl-4-methyltetrahydrofurans and 2-ethylidene-3,3-diphenyl-4-methyltetrahydrofuran, derived from the pyrolysis of the quaternary ammonium salts of the diastereomeric isomethadols and isomethadone, respectively, are reported. ¹H and ¹³C chemical shifts and ¹H-¹H coupling constants have been assigned in each case. The isomeric teterahydrofurans have been analyzed in terms of a half-chair conformation, and an envelope conformation for the ethylidene derivative.     

微量热法研究丹皮酚及其两种同分异构体与γ-环糊精在水溶液中的相互作用

在298.15 K下利用纳瓦级等温滴定微量热法研究了γ-环糊精与丹皮酚(Pae)及其两种同分异构体(2'-羟基-5'-甲氧基苯乙酮, Hma; 4'-羟基-3'-甲氧基苯乙酮, Ace)在水溶液中的相互作用, 并结合核磁共振对其相互作用的微观结构进行了表征. 试验表明, γ-环糊精与三种药物分子都是1∶1结合, 其中 Pae, Hma与γ-环糊精相互作用过程是焓驱动, 而Ace与γ-环糊精相互作用却是焓-熵共驱动; ¹H NMR 谱表明 Pae, Ace 与γ-环糊精形成典型的包结物, 其中 Pae 分子从 g-环糊精空穴的小口端进入, Ace分子从 g-环糊精空穴的大口端进入, 而 Hma 与γ-环糊精之间只是以弱相互作用结合而非包结作用. 结果显示γ-环糊精对三种同分异构体具有明显的分子识别功能.     

Identification of radiation‐induced radical structure in azocalix[4]arene: an EPR study

A macrocyclic azocalix[4]arene (1) based ester derivative was synthesized. The single crystals of azocalix[4]arene were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to ⁶⁰Co gamma rays with a dose rate of 0.980 kGy h^‐1 for 48 and 72 h to produce a stable free radical. Electron paramagnetic resonance (EPR) measurements were performed in three mutually perpendicular planes of the single crystal in the magnetic field, in addition, temperature dependence of the EPR signal was studied between 120 K and 450 K. The spectra were found to be temperature and angular dependent. Analysis based on the spectra recorded showed that a free radical was formed by fission of a C–H bond. This radical is described as ^?C_aHC_bH₃ The averages of the principal values of the hyperfine parameters and g‐factor are: g = 2.0034, A_Ha = 1.28 mT, A_H1=H2 = 1.00 mT, and A_H3 = 0.49 mT. Copyright © 2013 John Wiley & Sons, Ltd.