Collisionally activated mass spectra of [M?H] ions of polyhydroxy and hydroxy ether compounds

Collision-induced decomposition/mass-analyzed ion kinetic energy or collisionally activated mass spectra of [M ? H]^? ions of polyhydroxy compounds and other alcohols and ethers are reported. The [M ? H]^? ion of each compound is produced under OH^? negative ion chemical ionization mass spectrometric conditions. Characteristic fragmentations are observed that include production of [M ? H ? 2]^?, [M ? H ? 18]^? and [M ? H ? 32]^? ions. Certain other fragment ions in the collisionally activated mass spectra make it possible to distinguish among structural isomers. In polyhydroxy compounds, fragmentation increases as the number of hydroxyl groups increase, and carbon-carbon bond cleavage becomes favored.     

Studies on fungal metabolites—XXXI: Anthraquinonoid colouring matters of Penicillium islandicum sopp and some other fungi (−)luteoskyrin, (−)rubroskyrin, (+)rugulosin and their related compounds

The structures of (+)rugulosin, (?)luteoskyrin and (?)rubroskyrin have been reexamined by NMR and new structures 18, 19 and 20 proposed respectively. Their absolute structures were established on the basis of the X-ray analysis of (+)dibromodehydrotetrahydrorugulosin (27). The minor analogous metabolites, (?)4a-oxyluteoskyrin (31) of P. islandicum and (+)4a-oxyrugulosin (32) of P. brunneum, have been formulated. On oxidation of (?)luteoskyrin and (+)rugulosin with pertrifluoroacetic acid (?)4a,4a′-dioxyluteoskyrin (33) and (+>4a,4a′-dioxyrugulosin (34) were formed, while with MnO₂ (+)4a,4a′-dehydrorugulosin (35) was obtained. The structures of lumiluteoskyrin (37), and deoxylumiluteoskyrin (38), photooxidation products of luteoskyrin and deoxyluteoskyrin, respectively, have been elucidated.     

Isobutane chemical ionization mass spectra of unsaturated alcohols

Analysis of the isobutane chemical ionization mass spectra of hexenols, cyclohexenols and various syn/anti pairs of bicyclic and tricyclic homoallylic alcohols shows that: (i) the spectra of the allylic alcohols are dominated by [M + H – H₂O]⁺ and [M + C₄H₉–H₂O]⁺ ions and contain traces of [M + H]⁺ ions; (ii) [M + H]⁺ ions are prominent in the spectra of acyclic and certain cyclic homoallylic alcohols; and (iii) [M + H]⁺ ions dominate the spectra of other acyclic unsaturated alcohols. The [M + H]⁺ ions may result from either: (a) protonation of the hydroxyl group, followed by a very rapid intramolecular proton transfer from the protonated hydroxyl group to the carbon–carbon double bond or internal solvation of the protonated hydroxyl group by the carbon–carbon double bond; and/or (b) direct protonation of the carbon–carbon double bond with significant internal solvation of the resulting carbocation by the hydroxyl group, which may lead to carbon–oxygen bond formation to give a protonated cyclic ether. The consequences of placing various geometric constraints on the possible intramolecular interactions between the hydroxyl group and the carbon–carbon double bond in unsaturated alcohols are explored.     

1H, 13C, 15N and 195Pt NMR studies of Au(III) and Pt(II) chloride organometallics with 2‐phenylpyridine

¹H, ¹³C, ¹⁵N and ¹⁹⁵Pt NMR studies of gold(III) and platinum(II) chloride organometallics with N(1),C(2′)‐chelated, deprotonated 2‐phenylpyridine (2ppy*) of the formulae [Au(2ppy*)Cl₂], trans(N,N)‐[Pt(2ppy*)(2ppy)Cl] and trans(S,N)‐[Pt(2ppy*)(DMSO‐d₆)Cl] (formed in situ upon dissolving [Pt(2ppy*)(µ‐Cl)]₂ in DMSO‐d₆) were performed. All signals were unambiguously assigned by HMBC/HSQC methods and the respective ¹H, ¹³C and ¹⁵N coordination shifts (i.e. differences between chemical shifts of the same atom in the complex and ligand molecules: Δ^1H_coord = δ^1H_complex ? δ^1H_ligand, Δ^13C_coord = δ^13C_complex ? δ^13C_ligand, Δ^15N_coord = δ^15N_complex ? δ^15N_ligand), as well as ¹⁹⁵Pt chemical shifts and ¹H‐¹⁹⁵Pt coupling constants discussed in relation to the known molecular structures. Characteristic deshielding of nitrogen‐adjacent H(6) protons and metallated C(2′) atoms as well as significant shielding of coordinated N(1) nitrogens is discussed in respect to a large set of literature NMR data available for related cyclometallated compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

The Effect of C4H and C5H on the Microstructure of Aqueous Solutions of 1‐Alkyl‐3‐methylimidazolium Tetrafluoroborate Ionic Liquids

As is well‐known, the C2?H proton of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([Emim]BF₄) and 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim]BF₄) has a strong ability to form hydrogen bonds. The purpose of this work is to evaluate the effect of the interactions of the C4?H and C5?H protons on the microstructure of [Emim]BF₄ and [Bmim]BF₄ with water by using ¹H NMR spectroscopy. The differences between the relative ¹H NMR chemical shifts of C2?H, C4?H, and C5?H and between the interaction‐energy parameters obtained from these chemical shifts are minor, thus suggesting that the interactions of C4?H and C5?H may have a considerable effect on the microstructure. To confirm this, the viscosities of the systems are estimated by using the interaction‐energy parameters obtained from the ¹H NMR chemical shifts of the three studied aromatic protons and water, showing that the interactions of C4?H and C5?H also play an important role in the microstructure.     

Synthesis and electrochemical studies of heterobinuclear complexes containing copper and molybdenum nitrosyl groups linked by Schiff base ligands

The reaction of [MoCl(NO)T_p ^* = tris(3,5-dimethylpyrazolylborate] with copper Schiff base complexes derived by condensation of one mole each of 2,5-dihydroxybenzaldehyde and salicylaldehyde with α,ω diamines [NH₂(CH₂) _n NH₂, n = 2–4] yields heterobinuclear complexes with two potential redox centres. I.r., electronic and e.s.r. spectroscopic properties of these complexes are described. Cyclic voltammetric data of the base complexes in DMSO reveal that the copper redox centres undergo irreversible one electron reduction at potentials which vary slightly with the polymethylene carbon chain backbone of the Schiff base ligands. Incorporation of [MoCl(NO)T_p ^*]⁺ groups in the copper Schiff base complexes, results to a slight anodic shift (100 mV) in the reduction potential of the copper centre which remains invariant as the polymethylene carbon chain lengthens. Electrochemical data of the heterobinuclear complexes using CH₂Cl₂ and DMSO as solvents indicate the solvent dependence of the reduction potentials of these complexes. In CH₂Cl₂, the reduction potential of the copper centre shifts cathodically by 100 mV, while that of the molybdenum centre shifts anodically by 200 mV. However, accumulated electrochemical data of the heterobinuclear complexes indicate minimal electronic interactions between the copper and molybdenum redox centres. This revised version was published online in June 2006 with corrections to the Cover Date.     

13C and 1H chemical shifts in 2-benzylidene[3]ferrocenophane-1,3-diones. Elucidation of the substituent dependence of carbonyl chemical shifts in different carbonyl derivatives

The ¹³C and ¹H chemical shifts of the ferrocene moiety, as well as the carbonyl carbons and styrene moiety, of substituted 2-benzylidene[3]ferrocenophane-1,3-diones have been assigned. Correlations of ¹³C substituent chemical shifts of both carbonyl carbons with the Hammett constants have been found, and the effect of the transmission of substituent effects on these chemical shifts through the styrene moiety is discussed. An explanation is given for the different sensitivities of the carbonyl carbon chemical shifts to the electronic effect of substituents in mono- and dicarbonyl derivatives.     

The acid properties of dodecasubstituted porphyrins with a chemically active NH bond

The NH acid properties of nonplanar dodecasubstituted porphyrins (H₂P) were studied by the spectropotentiometric and spectrophotometric methods and by semiempirical quantum-chemical calculations. The reaction of H₂P with a weak organic base DMSO proceeded with the formation of the H-associated form DMSO?H?PH or DMSO?H?P?H?DMSO. Strong bases KOH[222] and [NR₄]OH reacted with the formation of mono-(HP^?) or dianionic (P^2?) forms. An increase in NH acidity along the series tetraphenylporphin < tetraphenyltetrabenzoporphin < β-octaethyltetraphenylporphin < dodecaphenylporphin < β-octabromotetraphenylporphin was to a great extent caused by the polarization of molecules, which accompanied saddle-nonplanar distortions of their structure, rather than β-substituent electronic effects. The quantitative characteristics obtained using the suggested system of criteria of the chemical activity of NH bonds (¹H NMR spectral, kinetic, and quantum-chemical criteria) linearly correlated with H₂P acid dissociation constants and could be used for alternative estimation of the acidity of tetrapyrrole compounds.     

Selenium-77 NMR chemical shifts of five-membered selenium and sulphur heterocycles with CSe,CS,and CO groups

This paper reports the ⁷⁷Se NMR chemical shifts of 1,3-dithiole-, 1,3-thiaselenole- and 1,3-diselenole-2-ones, -thiones and -selones, of the corresponding saturated compounds 1,3-diselenolane-2-one, -thione and -selone, and the 1,3-thiaselenolium tetrafluoroborates, either unsubstituted or substituted by morpholino, ethylthio or ethylseleno groups in the 2-position. The ⁷⁷Se chemical shift values of the ring selenium and the C?Se groups are compared with the ¹³C chemical shift values of neighbouring carbon atoms. The relationships between the ⁷⁷Se chemical shifts of the C?Se groups and the wavelengths of their n→* absorption in the UV-visible spectrum are discussed with respect to the significance of the δE term in the contribution of the paramagnetic screening and the electron density distribution.     

1H NMR spectra part 31: 1H chemical shifts of amides in DMSO solvent

The ¹H chemical shifts of 48 amides in DMSO solvent are assigned and presented. The solvent shifts Δδ (DMSO‐CDCl₃) are large (1–2 ppm) for the NH protons but smaller and negative (?0.1 to ?0.2 ppm) for close range protons. A selection of the observed solvent shifts is compared with calculated shifts from the present model and from GIAO calculations. Those for the NH protons agree with both calculations, but other solvent shifts such as Δδ(CHO) are not well reproduced by the GIAO calculations. The ¹H chemical shifts of the amides in DMSO were analysed using a functional approach for near ( ≤ 3 bonds removed) protons and the electric field, magnetic anisotropy and steric effect of the amide group for more distant protons. The chemical shifts of the NH protons of acetanilide and benzamide vary linearly with the π density on the αN and βC atoms, respectively. The C=O anisotropy and steric effect are in general little changed from the values in CDCl₃. The effects of substituents F, Cl, Me on the NH proton shifts are reproduced. The electric field coefficient for the protons in DMSO is 90% of that in CDCl₃. There is no steric effect of the C=O oxygen on the NH proton in an NH…O=C hydrogen bond. The observed deshielding is due to the electric field effect. The calculated chemical shifts agree well with the observed shifts (RMS error of 0.106 ppm for the data set of 257 entries). Copyright © 2014 John Wiley & Sons, Ltd.     

The NMR spectra of the carbanions of xanthene and thioxanthene. Evidence for paratropism

The proton NMR spectra of the carbanions of xanthene [XH]^? and thioxanthene [TxH]^? have been recorded and interpreted. Paratropism in the central rings of [XH]^? and [TxH]^? is inferred from a comparison of the chemical shifts with those of the carbanion of 9,10-dihydroanthracene [AH]^?. The contributions to the chemical shifts arising from n-electron excess charges, local dipoles and magnetic anisotropies are discussed. Numerical values for the various ring currents have been estimated by a least squares analysis of the observed chemical shifts after applying corrections for the excess charge effect. The results point to a strongly increasing paramagnetic ring current in the central ring in the order [AH]^?, [TxH]^?, [XH]^?.     

Charge transfer polymerization of 2-vinyl pyridine initiated by n-butyl amine and carbon tetrachloride

2-Vinyl pyridine (2-VP) can be initiated by a charge-transfer complex formed by the interaction of aliphatic amines such as n-butylamine (nBA) and carbon tetrachloride (CCl₄) in a solvent like NN-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). This article describes the polymerization of 2-VP by n-butylamine (nBA) in the presence of carbon tetrachloride in DMSO at 60°C. The rate of polymerization R_p increases rapidly with carbon tetrachloride (CCl₄) up to a concentration of 3.93 mol/L, but for a higher concentration it is almost independent of the carbon tetrachloride concentration; R_p is proportional to [nBA]^0.5 and [2-VP]^1.5 when [CCl₄]>[nBA]. The average rate constant k is 1.03 × 10^?5 L/mol s. When [CCl₄] < [nBA] the rate constant in terms of [2-VP] was 1.06 × 10^?5 s^?1 at 60°C and the overall rate constant was 1.035 × 10^?5 L/mol s at 60°C.     

Observed and calculated 1H and 13C chemical shifts induced by the in situ oxidation of model sulfides to sulfoxides and sulfones

A series of model sulfides was oxidized in the NMR sample tube to sulfoxides and sulfones by the stepwise addition of meta‐chloroperbenzoic acid in deuterochloroform. Various methods of quantum chemical calculations have been tested to reproduce the observed ¹H and ¹³C chemical shifts of the starting sulfides and their oxidation products. It has been shown that the determination of the energy‐minimized conformation is a very important condition for obtaining realistic data in the subsequent calculation of the NMR chemical shifts. The correlation between calculated and observed chemical shifts is very good for carbon atoms (even for the ‘cheap’ DFT B3LYP/6‐31G* method) and somewhat less satisfactory for hydrogen atoms. The calculated chemical shifts induced by oxidation (the Δδ values) agree even better with the experimental values and can also be used to determine the oxidation state of the sulfur atom (? S? , ? SO? , ? SO₂? ). Copyright © 2010 John Wiley & Sons, Ltd.     

Ortho effects in organic molecules on electron impact. Part 16. Novel oxygen transfers from the nitro group to acetylenic carbons in 2-nitrodiphenylacetylenes

Oxygen transfers to both acetylene carbons are noticed in parallel fragmentation pathways during the electron impact induced decompositions of 2-nitrodiphenylacetylene. The oxygen transfer to β-acetylenic carbon leads to the most abundant ion corresponding to benzoyl cation while transfer to the α-acetylenic carbon affords less intense fragments corresponding to [M? OH]⁺, [M? CO]^{+ ˙} and [M? CO₂]^{+ ˙}. The proposed fragmentation pathways and ion structures are supported by high-resolution data, linked-scan spectra and chemical substitution.     

Correlation between C and O chemical shifts and torsional strain in spiroacetals

The relationship between the ¹³C and ¹⁷O NMR chemical shifts and the dihedral energies (non-bonding interactions) of 1,4-dioxaspiro[4.4]nonane, 1,4-dioxa- and 6,10-dioxaspiro[4.5]decane, 1,4-dioxa- and 6,11-dioxaspiro[4.6]undecane, 1,5-dioxaspiro[5.5]undecane, 1,5-dioxa and 7,12-dioxaspiro[5.6]dodecane and 1,6-dioxaspiro[6.6]tridecane were analyzed. These data showed correlation of the non-bonding interactions with the chemical shift of the spiranic carbon, as well as a linear relationship between ¹³C and ¹⁷O.     

Structures de modeles de polyesters—I. Separation et etude par RMN [13C]des dihydroxy-2,3 butane, 2,4 pentane et 2,5 hexane et de leurs benzoates

[¹³C]NMR spectra have been obtained for a series of diols and benzoates, models of 2,3-dihydroxybutane, 2,4-dihydroxypentane and 2,5 dihydroxyhexane terephthalates after separation of diastereoisomers by gas and liquid-liquid chromatography. Chemical shifts for the meso and racemic derivatives have been interpreted in terms of rotational isomers. The results indicate that [¹³C]NMR is more sensitive than [¹H]NMR for the differentiation of diastereoisomers. Carbonyl and aromatic quaternary carbon chemical shifts are sensitive to the stereochemistry of the chain (long range effects) but relaxation times and nuclear Overhauser enhancements are identical in the two diastereoisomers.     

Long-range deuterium isotope effects on fluorine-19 chemical shifts of 4-substituted bicyclo[2.2.2]octyl- and bicyclo[2.2.1]heptyl-1-fluorides : Deuterium as a substituent

²H/¹H isotope effects on the ¹⁹F chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl and bicyclo[2.2.1]hept-1-yl fluoride are significantly shielding and deshielding, respectively. This result is consistent with deuterium being viewed as an $\text{electronegative}$ substituent relative to hydrogen when attached to an sp³ hybridised carbon.     

Carbon-13 nuclear magnetic resonance spectra of some mesoionic xanthine analogs

Natural abundance ¹³C NMR chemical shifts have been experimentally determined for a series of mesoionic thiazolo[3,2-a]pyrimidine-5,7-diones. The spectral data are compared with those of related mesoionic dihydrothiazolo[3,2-a]pyrimidine-5,7-diones and mesoionic 1,3,4-thiadiazolo[3,2-a]pyrimidine-5,7-diones. Resonable correlation between the observed ¹³C NMR chemical shifts and CNDO/2 total charge densities have been obtained for the different carbon atoms of 8-methylthiazolo[3,2-a]pyrimidine-5,7-dione.     

A study of lanthanide p-toluene sulphonic acid complexes in solution

Lanthanide p-toluene sulphonic acid (ptsa) complexes were prepared for La, Pr, Nd, Sm, Eu, Dy, Ho, Er and Yb, and found to exist as Ln(ptsa)₃. Conductivity studies of La(ptsa)₃ in DMSO and DMF suggest 1:2 and, possibly, 1:1 electrolyte behaviour in these solvents, respectively. NMR lanthanide-induced chemical shifts (LIS) for aromatic protons in (ptsa)^? and methyl protons in DMSO, were measured for all complexes as a function of the [Ln³⁺[DMSO] in a medium consisting of CCl₄, DMSO, and CH₃CN. Analysis of the LIS data suggests a change in (ptsa)^? coordination round Ln₃₊ across the lanthanide series.     

Linear Free‐Energy Relationships Applied to the 13C NMR Chemical Shifts in 4‐Substituted N‐[1‐(Pyridine‐3‐ and ‐4‐yl)ethylidene]anilines

Two series of 4‐substituted N‐[1‐(pyridine‐3‐ and ‐4‐yl)ethylidene]anilines have been synthesized using different methods of conventional and microwave‐assisted synthesis, and linear free‐energy relationships have been applied to the ¹³C NMR chemical shifts of the carbon atoms of interest. The substituent‐induced chemical shifts have been analyzed using single substituent parameter and dual substituent parameter methods. The presented correlations describe satisfactorily the field and resonance substituent effects having similar contributions for C1 and the azomethine carbon, with exception of the carbon atom in para position to the substituent X. In both series, negative ρ values have been found for C1′ atom (reverse substituent effect). Quantum chemical calculations of the optimized geometries at MP2/6‐31G++(d,p) level, together with ¹³C NMR chemical shifts, give a better insight into the influence of the molecular conformation on the transmission of electronic substituent effects. The comparison of correlation results for different series of imines with phenyl, 4‐nitrophenyl, 2‐pyridyl, 3‐pyridyl, 4‐pyridyl group attached at the azomethine carbon with the results for 4‐substituted N‐[1‐(pyridine‐3‐ and ‐4‐yl)ethylidene]anilines for the same substituent set (X) indicates that a combination of the influences of electronic effects of the substituent X and the π₁‐unit can be described as a sensitive balance of different resonance structures.