Deuteriochloroform Solution Research Articles

Solvent effects on the electronic and vibrational properties of high-valent oxomolybdenum(V) 5,10,15-triphenylcorrole probed by UV-visible and resonance Raman spectroscopy

Solution UV-visible electronic absorption and resonance Raman (RR) scattering spectra in 25 aprotic organic solvents have been measured and analyzed for a high-valent molybdenum( V ) oxo complex of 5,10,15-triphenylcorrole, (MoVO)CorPh3 . Optical absorption data in the visible region show a significant positive solvatochromism upon increasing solvent polarizability (ca. 660 cm-1 for the violet Soret band on going from acetonitrile to carbon disulfide), described by an excellent linear correlation between the bathochromic shifts of corrole π → π* electronic transitions and the solvent refractive index [Formula: see text]. Isotope labeling of the terminal oxo group with 18 O revealed the oxo-Mo(V) stretch of (MoVO)CorPh3 to vibrate at frequency ν(MoVO) ≈ 970 cm-1 [Δ(16O-18O) = 46 cm-1] , consistent with a MoV≡O triple bond. This vibration is greatly enhanced in the RR spectra with excitations within the Soret absorption band and its frequency is sensitive to solute-solvent interactions that weaken the MoV≡O triple bond by inhibiting O2- → Mo5+ electron donation. The ν(MoVO) frequency decreases in direct proportion to the Swain's solvent polarity parameter (A + B), from 969.4 cm-1 in n-hexane solution down to 955.6 cm-1 in dimethyl sulfoxide solution. However, only weak linear correlation was found when the ν(MoVO) frequencies were plotted as a function of the Gutmann's solvent acceptor numbers (ANs). A molecular association occurs between chloroform and (MoVO)CorPh3 through MoV≡O⋯H-CCl3 hydrogen-bonding interactions, manifested as an upshift of the ν(MoVO) RR band in deuteriochloroform solution. The ν(MoVO) stretching frequencies of (MoVO)CorPh3 and its fluorinated derivative (MoVO)Cor(Ph(CF3)2)3 {Cor(Ph(CF3)2)3 = 5,10,15-tris-[3,5-bis(trifluoromethyl)phenyl]corrole} are compared, and the increased strength of the MoV≡O bond in the latter oxo-Mo(V) species is attributed to the cis effect of the electron-withdrawing -C6H3(CF3)2 groups, as judged by a 6 cm-1 elevation of the ν(MoVO) frequency. Raman excitation profiles of ν(MoVO) and corrole skeletal vibrations show the presence of charge-transfer and π → π* electronic transitions within the Soret absorption band of oxomolybdenum( V ) corroles.

Di- n-octyltin(IV) complexes with 5-[( E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acid: Syntheses and assessment of solid state structures by 119Sn Mössbauer and X-ray diffraction and further insight into the solution structures using electrospray ionization MS, 119Sn NMR and variable temperature NMR spectroscopy

Reactions of 5-[( E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids (LHH′, where the aryl group is an R-substituted phenyl ring such that for L 1HH′: X = H; L 2HH′: X=2′-OCH 3; L 3HH′: X = 3′-CH 3; L 4HH′: X = 4′-CH 3; L 5HH′:X = 4′-Cl) with n Oct 2SnO in 2:1 and 1:1 molar ratios have been investigated. Two types of complexes, n Oct 2Sn(LH) 2 and {[ n Oct 2Sn(LH)] 2O} 2, were isolated and they have been characterized by 1H, 13C, 119Sn NMR, ESI-MS, IR and 119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The crystal structures of n Oct 2Sn(L 1H) 2 ( 1), {[ n Oct 2Sn(L 2H)] 2O} 2 ( 3) and {[ n Oct 2Sn(L 3H)] 2O} 2( 4) were determined. The mononuclear complex 1 was found to adopt a skew-trapezoidal bipyramidal arrangement around the tin atom while 3 and 4 are centrosymmetric tetranuclear bis(dicarboxylatotetrabutyldistannoxane) complexes containing a planar Sn 4O 2 core in which two μ 3-oxo O-atoms connect an Sn 2O 2 ring to two exocyclic Sn-atoms. The solution structures were confirmed by 119Sn NMR spectroscopy by observing one tin resonance in compound 1 and two tin resonances in {[ n Oct 2Sn(L 5H)] 2O} 2 ( 5). {[ n Oct 2Sn(L 2H)] 2O} 2 ( 3) and {[ n Oct 2Sn(L 3H)] 2O} 2 ( 4) undergo very complex exchange processes in deuteriochloroform solution, which has been confirmed by variable temperature 1H NMR spectroscopy. The cleavage of the most labile bond in the molecule was studied by ESI mass spectrometry.

Structure and tautomerism of azo coupling products from N-alkylenaminones derived from acetylacetone and benzoylacetone in solid phase and in solution

A series of azo coupling products have been prepared by reaction of substituted benzenediazonium tetrafluoroborates with N-alkyl 4-aminopent-3-en-2-ones or 3-amino-1-phenylbut-2-en-1-ones. The structure and tautomerism of the reaction products were studied by means of single-crystal X-ray study and by NMR spectroscopy in deuteriochloroform solution. The azo coupling products obtained from 4-methylaminopent-3-en-2-ones (3a–i) exist in CDCl3 solution as E/Z isomer mixtures with the Z isomer strongly predominating. The major isomer is a mixture of enamino–azo and imino–hydrazo tautomers with the former predominating. The proportion of the azo form depends on substitution of the benzene ring of the diazonium salt and decreases in the order of MeO > Me > Br > NO2. The position of tautomeric equilibrium is practically unaffected by switching from 4-methylaminopent-3-en-2-ones to 3-methylamino-1-phenylbut-2-en-1-ones. In the solid phase, the azo form always predominates; substitution of diazonium salt and at N3 nitrogen does not significantly affect the position of the tautomeric equilibrium. The azo coupling products always exist in the form of a single Z isomer. All determined structures, in the solid state, consist of a mixture of the two tautomeric forms, amino–diazenyl and imino–hydrazone, in ratios ranging from 82/18 to 91/9%. The weighed superimposition of both the hydrogen-bonded N1N2–C1C2–N3H/ HN1–N2C1–C2N3 heterodienic fragments, however, do not allow to clarify the effects of the para-substituents at the N1-phenyl ring both on the N1⋯N3 hydrogen-bond distances and on the bond lengths in the heterodienic systems within the series 3a–c,f and 4a–c,e,f.

15N NMR chemical shifts of ring substituted benzonitriles

15N chemical shifts in an extensive series of para (15) and meta (15) as well as ortho (8) substituted benzonitriles, X-C6H4-CN, were measured in deuteriochloroform solutions, using three different methods of referencing. The standard error of the average chemical shift was less than 0.03 ppm in most cases. The results are discussed for both empirical correlations with substituent parameters and quantum chemical calculations. The 15N chemical shifts calculated at the GIAO/B3LYP/6-31 + G*//B3LYP/6-31 + G* level reproduce the experimental values well, and include nitrogen atoms in the substituent groups (range of 300 ppm with slope 0.98 and R = 0.998, n = 43). The 15N shifts in hydroxybenzonitriles are affected by interaction with the OH group. Therefore, these derivatives are excluded from the correlation analysis. The resultant 15N chemical shift correlates well with substituent constants, both in the simple Hammett or DSP relationships and the 13C substituent-induced chemical shifts of the CN carbon.

Synthesis and characterization of bis[dicarboxylatotetraorganodistannoxane] units involving 5-[( E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids: An investigation of structures by X-ray diffraction, NMR, electrospray ionisation MS and assessment of in vitro cytotoxicity

Reactions of 5-[( E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids (LHH′, where the aryl group is an R-substituted phenyl ring such that for L 1HH′: R = H; L 2HH′: R = 2′-CH 3; L 3HH′: R = 3′-CH 3; L 4HH′: R = 4′-CH 3; L 5HH′: R = 4′-Cl; L 6HH′: R = 4′-Br) with n Bu 2SnO in a 1:1 molar ratio yielded complexes of composition {[ n Bu 2Sn(LH)] 2O} 2. The complexes have been characterized by 1H, 13C, 119Sn NMR, ESI-MS, IR and 119 m Sn Mössbauer spectroscopic techniques in combination with elemental analyses. The crystal structures of {[ n Bu 2Sn(L 1H)] 2O} 2 ( 1), {[ n Bu 2Sn(L 4H)] 2O} 2 ( 4), {[ n Bu 2Sn(L 5H)] 2O} 2 ( 5) and {[ n Bu 2Sn(L 6H)] 2O} 2 ( 6) were determined. The compounds are centrosymmetric tetranuclear bis(dicarboxylatotetrabutyldistannoxane) complexes containing a planar Sn 4O 2 core in which two μ 3-oxo O-atoms connect an Sn 2O 2 ring to two exocyclic Sn-atoms. The four carboxylate ligands display two different modes of coordination where both modes involve bridging of two structurally distinct Sn-atoms. The solution structures were confirmed by 119Sn NMR spectroscopy by observing two tin resonances in compounds 1, and 4– 6. The observed difference between the two tin resonances was about 3 ppm while the differences in 13C resonances were even smaller. Compounds {[ n Bu 2Sn(L 2H)] 2O} 2 ( 2) and {[ n Bu 2Sn(L 3H)] 2O} 2 ( 3) undergo a very complex exchange processes in deuteriochloroform solution. The in vitro cytotoxic activity of compounds 1 and 4 against WIDR, M19 MEL, A498, IGROV, H226, MCF7 and EVSA-T human tumour cell lines is reported.

Catalysis of aminolysis of p‐nitrophenyl acetate by 2‐pyridones

AbstractThe influence of a series of alkyl‐substituted 3‐cyano‐2‐pyridones on the kinetics of the reaction of p‐nitrophenyl acetate (10) with n‐butylamine (9) was studied. The reactions were monitored under pseudo‐first‐order conditions using an excess of n‐butylamine by 1H NMR spectroscopy at 23°C in CDCl3. A non‐linear dependence of the observed rate constants kobs on the pyridone concentration was observed in all cases. The results were analysed using two different kinetic models. The first model is based on the amine‐catalysed background reaction in combination with a pyridone‐catalysed process, whose efficiency is reduced through dimerization of the pyridone catalyst to an inactive dimer. The second model also involves the amine‐catalysed background process, now in combination with a catalysed process proceeding through pre‐equilibrium complexation of the substrate with a 1:1 amine–pyridone complex and a second (rate‐determining) step involving C—N bond formation. In addition to these kinetic studies, the aggregation behaviour of pyridones 2 and 3 was also studied in pure deuteriochloroform solutions and mixtures of n‐butylamine and deuteriochloroform. While substantial aggregation to dimers occurs for both pyridones in deuteriochloroform, no such dimerization appears to occur in deuteriochloroform solutions containing 250 × 10−3 mol l−1 n‐butylamine. This finding strongly supports kinetic model 2 as the more realistic choice. Copyright © 2005 John Wiley & Sons, Ltd.

2D 1H and 13C NMR evidences of the [2+2] autodimerization of 2-benzyl-5-benzylidene cyclopentanone yielding two different diphenyl, dispiro cyclobutane derivatives

The ene-ene [2+2] cycloaddition of 2-benzyl-5-benzylidenecyclopentanone proceeds smoothly and spontaneously in benzene-d 6 or deuteriochloroform solution to give two different diphenyl dispiro [4.1.4.1] dodecan-4,11-diones. Detailed 1H and 13C 2DNMR spectroscopy (COSY, HMQC, HMBC) were performed in order to prove the existence in solution of two cyclobutane derivatives, one a previously described photodimer obtained by the UV irradiation of crystals of 2-benzyl-5-benzylidenecyclopentanone.

Molecularly Imprinted Polymers (MIPs) Against Uracils: Functional Monomer Design, Monomer-Template Interactions In Solution And MIP Performance In Chromatography

AbstractThe interaction of N1-substituted uracils (cyclohexyl (1) and benzyl (2)) with three polymerisable recognition elements, the novel monomers 9-(3/4-vinylbenzyl)adenine (3) and 2,6-diamino-9-(3/4-vinylbenzyl)purine (4) and the previously synthesised monomer 2,6-bis(acrylamido)pyridine (5), has been studied via1H NMR in deuterio-chloroform solution. MIPs against (2) have been prepared using each of the monomers and tested in the chromatographic mode. The effect of the number and type of hydrogen bonds formed between the templates and the functional monomers is reflected in the values of the apparent association constants obtained from the solution study and by the performance of the subsequently prepared MIPs in the chromatographic mode.

Flat Peptides

We have synthesized by solution methods the first homopeptide series, pBrBz-(ΔAla)n-OMe (n = 1−6), based on a Cα,β-didehydro-α-amino acid, to determine the preferred conformation of this residue, characterized by an sp2 α-carbon atom and the smallest side chain. To this aim, we have exploited FTIR absorption and 1H NMR techniques in solution and X-ray diffraction in the crystal state. Our investigation shows that a multiple, consecutive, fully extended conformation (2.05-helix) largely predominates for all oligomers in deuteriochloroform solution and occurs in the crystal state for the monomer, dimer, and trimer as well. These peptide molecules are completely flat, including the amino acid side chains, and form planar sheets. This novel peptide structure is stabilized by two types of intramolecular H-bonds, Ni−H···OiC‘i (typical of the 2.05-helix) and Cβi+1−H···OiC‘i (characteristic of ΔAla peptides). The results obtained are compared with those of the oligopeptides based on the related Cβ-substituted, Cα,β-didehydro-α-amino acid residues.

Saturated heterocycles. 251. Determination of σ+ values of heteroaryl‐substituted phenyl groups via ring‐chain tautomerism

AbstractThe Hammett‐Brown electrophilic substituent constants σ+ for five heteroaryl‐substituted phenyl groups were estimated via the ring‐chain tautomeric equilibria of three sets of oxazolidines and 1,3‐oxazines in deuteriochloroform solution. For oxazolidines derived from norephedrine and norpseudoephedrine, the σ+ values were also determined via the gas‐phase ring‐chain equilibria, by means of mass spectrometry. The results show that the heteroaromatic substituents studied have a slight electron‐withdrawing character, with σ+ in the range ‐0.03 to 0.59. The gas‐phase σ+ values are significantly higher than the solution values.

Aryl Ring Rotation in Porphyrins. A Carbon-13 NMR Spin−Lattice Relaxation Time Study

Overall tumbling and internal rotational motions in porphyrins bearing meso aryl substituents and, in some cases, flanking alkyl groups at the β-pyrrolic positions have been determined using 13C spin−lattice relaxation time measurements. In deuteriochloroform solution at 303 K, the overall reorientation of all three porphyrins investigated occurs with diffusion coefficients of ∼1 × 109 s-1. In porphyrins with only hydrogen at the β-pyrrolic positions, the meso phenyl rings undergo rotations about their single bonds to the porphyrin with diffusion coefficients of ∼4 × 109 s-1. Introduction of methyl substituents at the β-pyrrolic positions adjacent to the phenyl rings reduces these motions, but only to ∼1 × 109 s-1. Thus, significant internal motions are present in both types of molecules. These motions occur on the time scale of many photoinduced electron and energy transfer processes in porphyrins covalently linked to electron or energy donors or acceptors through meso aryl groups. Thus, the internal lib...

Preparation and deposition of stable monolayers of fullerene derivatives

Two new fullerene derivatives have been synthesized, which tend to form Langmuir monolayers. Robust monomolecular layers are formed at the air/water interface, that can be transferred onto hydrophilic substrates by Langmuir–Blodgett or Langmuir–Schaefer techniques. The measured areas per molecule (105 Å2 for 1a dropped from a deuteriochloroform solution at 20 °C) reach those expected for a true monolayer of C60 at the air/water interface.

Silicon-29 NMR Spectra of Trimethylsilylated Alcohols

29Si NMR spectra of trimethylsilyl (TMS) derivatives of 26 simple alcohols were measured under standardized conditions (i.e., in sufficiently diluted deuteriochloroform solutions). Due to association with the solvent the chemical shifts are in almost all cases larger than those reported earlier for different solutions. This observation is in agreement with the proposed mechanism of steric effects as being due to sterically controlled association with the solvent. The use of chloroform as a solvent enhances steric effects but at the same time it can reduce small differences due to polar effects in closely related compounds. In the studied class of compounds the gross dependence of the chemical shift on polar effects is not substantially affected by the change of the solvent.

Acylaminoacetyl derivatives of active methylene compounds. 4

AbstractMeldrum's acid has been found to be effectively acylated using the imidazolides of N‐protected glycines, X‐NHCH2COOH (X = ‐COPh, ‐COMe, ‐Z, ‐Boc, ‐COOMe and ‐COOEt). The corresponding C‐acylation compounds were isolated in high yields and were readily converted to the N‐protected tetramic acids. It was shown by pmr spectroscopy that these acids exist as the enol tautomers in DMSO‐d6 solution, whereas in deuteriochloroform solution both the enol and keto tautomers can be observed.

Use of shaped pulses for semi‐selective excitation of imino 1H resonances in duplex DNA and RNA

AbstractThe application of shaped pulses, e.g. TOPHAT and hyperbolic secant, for the semi‐selective excitation of the imino 1H resonances of duplex DNA and RNA in aqueous solution is explored. The excitation profiles for the shaped pulses are calibrated on a sample containing a mixture of A:U base pairs in deuteriochloroform solution. The data obtained by performing a semi‐selective inversion‐recovery pulse sequence using a TOPHAT waveform for the 90° pulse and a hyperbolic secant waveform for the 180° pulse are fitted well by a single exponential function, are independent of transmitter offset over a 1 kHz bandwidth and are in good agreement with the value obtained with hard rectangular pulses. This approach for measuring T1 values was applied to a 2 mM sample of a self‐complementary oligoribonucleotide containing the nucleoside analogue 5‐fluorouridine in 90% H2O. The T1, values were calculated as a function of Tris concentration, a catalyst added to promote imino hydrogen exchange. The T1, values were obtained by good fits of single exponential functions to the inversion‐recovery data. The T1, values depend on the concentration of added Tris. Shaped pulses provide a convenient alternative to long rectangular pulses and hard pulse trains for the semi‐selective excitation of imino 1H resonances.

Electron‐nuclear relaxation time T1e for intramolecular distance evaluation

AbstractCarbohydrate molecules labelled by TEMPOL nitroxide radicals in dilute deuteriochloroform solutions are considered. The distances between 13C nuclei and the nitroxide free electron are related to the measured contributions to the 13C longitudinal relaxation rates which stem from the dipolar coupling with the electron spin. It is shown that a correct interpretation of these electron‐nuclear relaxation times rests on an accurate knowledge of the effective viscosity experienced by the labelled solute. This microviscosity can be roughly estimated from a simple hydrodynamic model which takes the difference in sizes of the solute and solvent molecules into account. A more accurate experimental determination is obtained by measuring the electron‐nuclear relaxation times of the cyanide 13C spin on a rigid cyano‐TEMPOL radical used as a microviscosity probe. Various models of rotational diffusion are considered. The anisotropy of the rotational motion of the labelled sugar and a possible contraction‐expansion of the electron‐13C distances due to dynamic conformational changes are examined, and their effects on the relaxation times are calculated. The delocalization of the paramagnetic free electron is taken into account, and a theoretical model for calculating its influence on the relaxation is presented. To our knowledge, this is the first study showing the importance of the electronic spin delocalization which reduces the relaxation times by a factor of 2 for the cyano‐TEMPOL. Using a theory which incorporates the correct microviscosity, rotational anisotropy and free electron delocalization, the electron‐13C distances of the labelled sugar, which give theoretical relaxation times in agreement with the experimental data, are found to be nearly equal to the values determined by X‐ray studies. The solute appears to have a stretched rigid shape in chloroform over a large temperature range. Electron‐nuclear relaxation studies allow the evaluation of intramolecular interspin distances up to 10–15 Å in length with an accuracy of about 5%.

On triazoles XXX. Synthesis of [1,2,4]triazolo‐[1,5‐d][1,2,4,6]tetrazepine‐5‐thiones

AbstractDifferent 2‐Q‐6,7,8,9‐(bi‐, tri‐ or tetra)substituted[1,2,4]triazolo[1,5‐d][1,2,4,6]tetrazepine‐5‐triione derivatives representing a novel ring system were synthesised. In the case of 8‐aryl‐substituted derivatives ring‐chain tautomerism was observed in DMSO‐d6 or deuteriochloroform solutions. In some cases both ring and chain tautomers could be isolated in crystalline form. The structure of products obtained was proved by nmr using also model compounds prepared for this purpose.

Multinuclear NMR study of some diorgano(chloro)tin(IV) oxinates and thiooxinates

The 119Sn, 15N, 13C and 1H NMR aswell as the solid state 119Sn CP-MAS NMR spectra have been used to study the structures of four diorgano(chloro)tin(IV) oxinates and thiooxinates, (C 6H 5) 2Sn(Cl)(oxin) and R 2Sn(Cl)(Txin), where R = benzyl, phenyl, or vinyl groups, oxin = 8-quinolinolate, txin = 8-quinolinethiolate, in deuteriochloroform solution and in the solid state. Both in a non-coordinating solvent (CDCl 3) and in the solid state the compounds studied are formed by monomeric molecular chelate complexes with a distorted cis-trigonal bipyramidal arrangement of coordination polyhedra centred on a five-coordinated tin atom. The fine structure of the centre-bands in the 119Sn CP-MAS spectra can qualitatively be explained as result of the combined effect of residual dipolar coupling and scalar interaction of the 119Sn nucleus with two different quadrupolar nuclei ( 14N, I = 1; 35,37Cl, I = 3 2 ).

Stability of (chloromethyl)platinum(II) complexes

The stabilities of [Pt(CH2Cl)2(cod)], [Pt(CH2Cl)Cl(cod)](cod = cycloocta-1,5-diene) and a range of phosphine-containing mono- and cis-bis-(chloromethyl)platinum(II) complexes have been investigated in deuteriochloroform at room temperature. Some of the bis(chloromethyl) derivatives appear to be indefinitely stable (cod and chelating arylphosphines), others suffer very slow decomposition to the dichlorides (non-chelating arylphosphines), and the remainder decompose relatively rapidly, and cleanly, to the dichlorides plus ethylene (alkylphosphines, non-chelating faster than chelating). Rapid decomposition of the arylphosphine complexes can be induced by adding hexafluoroisopropyl alcohol to the deuteriochloroform solutions. Attempts to generate [Pt(CH2Cl)2{P(C6H11)3}2] by addition of P(C6H11)3 to [Pt(CH2Cl)2(cod)] resulted in the formation of cis-[Pt–{CH2CH2P+(C6H11)3}Cl2{P(C6H11)3}]; a mechanism is proposed. All cis-mono(chloromethyl) derivatives studied appear to be indefinitely stable. In contrast, the trans-mono(chloromethyl) complexes, although stable in very dry solvent, undergo decomposition in the presence of moisture to the corresponding hydrides plus formaldehyde; a mechanism is proposed. The hydrides undergo subsequent conversion into a mixture of cis and trans dichlorides.

ChemInform Abstract: 29Si and 13C NMR Spectra of Trimethylsiloxy and Hydroxy Adamantanes Reinvestigated at Low Concentration in Deuteriochloroform Solutions.

29 Si and 13 C NMR chemical shifts are reported for mono- and bis(trimethylsiloxy)adamantanes as well as for mono- and dihydroxyadamantanes dissolved in deuteriochloroform. The chloroform induced changes in 29 Si and 13 C chemical shifts can be qualitatively accounted for by hydrogenbonding considering basicity and solvent accessibility of oxygen atoms in the solute molecules. The steric effects observed on the 29 Si shifts are not due to an interaction of the terminal hydrogen atoms of the trimethylsilyl groups but are due to proximity of two oxygen atoms on one cyclohexane ring of the adamantane skeleton