Etude des copolymeres (ethylene-hexene-1) par resonance magnetique nucleaire du proton et du carbone 13

Ethylene 1-hexene copolymers obtained by catalytic polymerization have been examined by ¹H and ¹³C NMR. Copolymer compositions have been determined by ¹H NMR and i.r. and the sequence distributions for 1-hexene by ¹³C NMR. Variations of the copolymer microstructure have been related to the experimental conditions for copolymerization.     

Synthesis,Spectroscopic Studies,and In Vitro Antifungal Activity of Organosilicon(IV) and Organotin(IV) Complexes of 4-Amino-5-mercapto-3-methyl-S-triazole Schiff Bases

The Schiff bases derived from condensation of s-triazole with heterocyclic aldehydes and their 1:1 and 1:2 complexes have been synthesized. These complexes have been characterized by elemental analyses, molar conductance and spectroscopic studies, including UV, IR, ¹H, ¹³C, ²⁹Si, and ¹¹⁹Sn NMR spectroscopy. On the basis of these studies, the resulting complexes have been proposed to have trigonal bipyramidal and octahedral geometries. The biological activity of these complexes against various fungi has been investigated.     

Synthèse de la désamino1-Orn8-vasopressine,de la désamino1-Phe2-Orn8-vasopressine,de la désamino1-Ile3-Orn8-vasopressine (= désamino1-Orn8-oxytocine) et de la désamino1-Phe2-Ile3-Orn8-vasopressine (= désamino1 -Phe2-Orn8-oxytocine)

Four analogues of the vasopressins have been synthesised: Deamino¹-Orn⁸-vasopressin, Deamino¹-Phe²-Orn⁸-vasopressin, Deamino¹-Ile³-Orn⁸-vasopressin (= Deamino¹-Orn⁸-oxytocin) and Deamino¹-Phe²-Ile³-Orn⁸-vasopressin (= Deamino¹-Phe²-Orn⁸-oxytocin). The two former have been prepared by condensation of tripeptide azides with an hexapeptide. The two latter have been obtained from the hexapeptide by the recurring method, using active trichlorophenyl esters.     

Synthesis and characterization of some α-naphthyl selenium/tellurium derivatives: X-ray crystal structure of benzyl-1-naphthyl selenide and diphenylmethyl-1-naphthyl selenide

A large number of α-naphthyl selenium and tellurium compounds (1-14) have been prepared through two different methods. The first method involves the alkylation of sodium 1-naphthylselenolate/tellurolate, generated in situ using hydrazine hydrate as reducing agent while the second method involves the reaction of in situ generated α-naphthylseleno/telluromagnesium bromide with an appropriate electrophile. The synthesized alkyl-1-naphthyl selenides/tellurides and some α,ω-bis(1-naphthylseleno)alkanes have been characterized with the help of elemental analysis and using various spectroscopic techniques viz., NMR (¹H, ¹³C, ⁷⁷Se and ¹²⁵Te), IR, UV/vis spectroscopy and mass spectrometry (only in few representative cases). Interpretation of ¹H, ¹³C NMR spectra and assignment of individual resonances for tris(1-naphthylseleno)methane have been done with the help of [¹H-¹H] and [¹H-¹³C] correlation spectroscopy (COSY). X-ray crystallographic results and molecular geometry of benzyl-1-naphthyl selenide, 2 and diphenylmethyl-1-naphthyl selenide, 3 have also been illustrated.     

NMR study of 1-azatricyclo[3.3.1.13-7]decane derivatives

1-Azatricyclo[3.3.1.1^3-7]decan-4-one (4-oxo-1-azaadamantane) and 1-azatricyclo[3.3.1.1^3-7]decane-4-α(β)-ol (4-α-(β)-hydroxy-1-azaadamantane) have been studied by ¹H and ¹³C nmr methods. From this study several stereo and stereoelectronic effects have been deduced. The complete proton and carbon chemical shift assignments for the title compounds have been made, with the aid of two-dimensional nmr techniques.     

Aromatic imine stereochemistry as studied by 13C and 1H NMR of 15N-enriched materials

A series of thirteen ¹⁵N-enriched N-aryl imines derived from benzaldehydes and acetophenones have been prepared and examined by ¹³C and ¹H NMR. Preferred conformations of the C-arvl and N-aryl rings have been deduced from ¹³C chemical shifts and ¹³C-¹⁵N couplings. Evidence for steric inhibition of resonance in O-alkylated materials is presented. Relative signs of ¹J(CN) and ²J(CCN) have been determined in some compounds. An E: Z interconversion barrier of 21.6 kcal mol^?1 has been obtained from ¹H NMR coalescence data.     

Diode laser spectra of cis-HONO near 850 cm−1 and trans-HONO near 1700 cm−1

Tunable diode laser spectra have been measured for the ν₄ band of cis-HONO near 850 cm^?1 and the ν₂ band of rans-HONO near 1700 cm^?1. The ν₄ band is completely unperturbed and 355 well-resolved transitions have been fit with a standard deviation of 0.0007 cm^?1. The ν₂ band appears to have some small perturbations, but about 190 transitions have been fit with a standard deviation of 0.0027 cm^?1. Rotational and centrifugal distortion constants are given for both bands.     

A route to magnetically separable nanocatalysts: Combined experimental and theoretical investigation of alkyl substituent role in ligand backbone towards epoxidation ability

We have prepared two chiral Schiff base ligands, H₂L¹ and H₂L², and one achiral Schiff base ligand, H₂L³, by treating 2,6‐diformyl‐4‐methylphenol separately with (R )‐1,2‐diaminopropane, (R )‐1,2‐diaminocyclohexane and 1,1′‐dimethylethylenediamine, in ethanolic medium, respectively. The complexes MnL¹ClO₄ ( 1 ), MnL²ClO₄ ( 2 ), MnL³ClO₄ ( 3 ), FeL¹ClO₄ ( 4 ), FeL²ClO₄ ( 5 ) and FeL³ClO₄ ( 6 ) have been obtained by reacting the ligands H₂L¹, H₂L² and H₂L³ with manganese(III) perchlorate or iron(III) perchlorate in methanol. Circular dichroism studies suggest that ligands H₂L¹ and H₂L² and their corresponding complexes have asymmetric character. Complexes 1 – 6 have been used as homogeneous catalysts for epoxidation of alkenes. Manganese systems have been found to be much better than iron counterparts for alkene epoxidation, with 3 as the best catalyst among manganese systems and 6 as the best among iron systems. The order of their experimental catalytic efficiency has also been rationalized by theoretical calculations. We have observed higher enantiomeric excess product with catalysts 1 and 4 , so they were attached to surface‐modified magnetic nanoparticles to obtain two new magnetically separable nanocatalysts, Fe₃O₄@dopa@MnL¹ and Fe₃O₄@dopa@FeL⁴. They have been characterized and their alkene epoxidation ability has been investigated. These catalysts can be easily recovered by magnetic separation and recycled several times without significant loss of catalytic activity. Hence our study focuses on the synthesis of a magnetically recoverable asymmetric nanocatalyst that finds applications in epoxidation of alkenes and at the same time can be recycled and reused.     

Reactions of (E)-4-Stilbenethiole with Dibromoalkanes

New substituted stilbenes have been prepared by reactions of (E)-4-stilbenethiole with dibromoalkanes. ¹H and ¹³C NMR spectra of new compounds have been assigned unambiguously on the basis of a combination of homo- (¹H?¹H COSY) and heteronuclear (¹ H?¹³C COSY-HETCOR) two-dimensional methods, chemical shifts, and spin-coupling constants.     

Vibrational spectra,methyl torsional potential functions,internal rotational potential functions,and conformational properties of ethyl vinyl ether

The vibrational spectra of ethyl vinyl ether in both the fluid and solid states have been recorded from 20 to 3500 cm^?1. The 33 fundamental modes of vibration have been assigned. Three rotational isomers have been observed and their structures have been determined. The most stable conformer, s-cis/s-trans, is planar and of C_s symmetry. The two less stable rotamers, skew/s-trans and skew/gauche, are non-planar and of C_i molecular symmetry. The barrier to internal rotation of the methyl rotor has been determined for each conformation; these barriers are 3.43 kcal mol^?1 (s-cis/s-trans), 3.35 kcal mol^?1 (skew/s-trans) and 3.19 kcal mol^?1 (skew/gauche). A potential function for each of the two asymmetric internal rotations has been calculated and barriers to conformer interconversion have been determined. From the asymmetric potential function calculations, ΔH, the enthalpy difference between the conformers, has been determined. The s-cis/s-trans conformer is 1.87 kcal mol^?1 more stable than the skew/s-trans conformer; the skew/s-trans conformer is more stable than the skew/gauche conformer by 1.10 kcal mol^?1. The energetics of conformer interconversion and methyl internal rotation have been described in terms of molecular geometry and non-bonded interactions. These results are compared to those found in other alkyl vinyl and dialkyl ethers.     

Synthesis of Indeno[2′,1′:5,6]pyrido[2,3‐d]pyrimidine Derivatives and Their Recognition Properties as New Type Anion Receptors

A new type anion receptors containing indeno[2′,1′:5,6]pyrido[2,3‐d]pyrimidine have been synthesized via three‐component reaction of aldehyde, 6‐aminopyrimidine‐2,4‐dione, and 1,3‐indanedione in aqueous media. The binding properties of the receptors with anions such as F^?, Cl^?, Br^?, AcO^?, HSO₄^?, and H₂PO₄^? have been investigated by UV–vis spectroscopy methods. The results have shown that receptors have good selectivity to F^? and AcO^?, and a 1:1 stoichiometry complex has been formed between compounds and anions.     

Theoretical structure of the low‐laying electronic states of the molecule YBr

An ab initio CASSCF and MRCI (single and double excitation plus Davidson correction) calculation have been performed for the molecule YBr. The potential energy curves of 20 electronic states in the representation ^2s+1Λ^(+/?) (neglecting the spin‐orbit effects) and 41 states in the representation Ω^(+/?) [including the spin‐orbit (SO) effects] have been calculated along with the corresponding spectroscopic constants. The SO effects are taken into account via a semi‐empirical SO pseudo‐potential for the yttrium atom, while they have been neglected for bromine. Very good agreement is displayed by comparing the present results with those obtained experimentally, up to now, of the three states X¹Σ⁺, (1)²Π, and (2)¹Σ⁺. New results have been obtained for 17 states ^2s+1Λ^(+/?), and their SO components yet not observed or calculated. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

New Oenotheralanosterol A and B Constituents from the Oenothera biennis Roots

Two new compounds oenotheralanosterol A and B along with four known compounds have been isolated from the roots of Oenothera biennis. Their structures have been elucidated with the help of 300 MHz NMR using 1D and 2D spectral methods viz: ¹H and ¹³C NMR, ¹H‐¹H COSY, ¹H‐¹³C HETCOR and DEPT aided by EIMS, ESI Mass and IR spectroscopy.     

Enthalpies of fusion and solid-to-solid transition,entropies of fusion for urea and twelve alkylureas

Enthalpies and temperatures of fusion have been measured by differential scanning calorimetry for urea and a number of its mono- and di-alkyl derivatives. Enthalpies obtained are: urea, 14.79 kj mol⁻¹; monomethylurea, 15.75 kJ mol⁻¹ ; monoethylurea, 13.94 kJ mol⁻¹ ; monopropylurea, 14.63 kJ mol⁻¹ ; monoisopropylurea, 17.40 kJ mol⁻¹ ; monobutylurea, 14.55 kJ mol⁻¹ ; monotertbutylurea, 33.13 kJ mol⁻¹ ; dimethyl-1,1 urea, 29.61 kJ mol⁻¹ ; dimethyl-1,3 urea, 13.62 kJ mol⁻¹; diethyl-1,1 urea, 16/78 kJ mol⁻¹ ; diethyl-1,3 urea, 12.46 kJ mol⁻¹ ; dibutyl-1,3 urea, 14.87 kJ mol⁻¹; trimethyl-1,1,3 urea, 14.30 kJ mol⁻¹. Entropies of fusion have been derived from the experimental results.By temperature scanning starting from r.t. some solid-to-solid transitions for four alkylureas have also been detected, all hitherto unreported. Temperatures and enthalpies of transition are: for monoisopropylurea, 375.5 K and 2.31 kJ mol ⁻¹ ; for monobutylurea (two transitions), 313.1 K and 7.02 kJ mol⁻¹ , 344.9 K and 0.88 kJ mol⁻¹ ; for diethyl-1,3 urea, 339.4 K and 1.87 kJ mol⁻¹ ; for dibutyl-1,3 urea, 311.5 K and 11.10 kJ mol⁻¹.     

Ab initio potential energy curves and transition dipole moments for the interaction of a ground state He with Na(3s–3p)

Potential energy curves of the states X ²Σ⁺, B (1)²Σ⁺ and A (1)²Π of the NaHe molecule have been calculated accurately in a large range of internuclear distances R from SA-CASSCF-MRCI calculations, using molecular orbitals expanded in cc-pV5Z basis sets. Transition dipole moments have also been calculated for the X–B, X–A and A–B transitions, in the same range of R. Their long-range behaviour have been considered.     

β-Diketonates of Cyclopalladated Arylazonaphthalenes: Synthesis, Characterization and Redox Activity

The synthesis of monomeric mixed species of the type [PdLK] (L = cyclopalladated arylazonaphthalenes) have been achieved by splitting the halogeno-bridge in [Pd₂L₂Cl₂] by β-diketones (HK). The compounds have been characterized on the basis of spectral (IR, UV–VIS, FAB mass, ¹H and ¹³C{¹H}NMR) and elemental analysis data. Some of the [PdLK] cyclometallates occur as isomeric mixtures whose composition have been established by ¹H-NMR data. Electron transfer properties of the cyclopalladates in DMF have been thoroughly examined using cyclic voltammetry.     

Raman and resonance-Raman spectra of CsI/I−3

Raman and resonance-Raman spectra of the I^?₃ ion isolated within CsI crystals have been studied using 647 nm and 488 nm exciting radiation. Sample temperatures between 300 and 20 K have been used. Eleven overtones of the symmetric stretching mode (nν₁) have been observed in the resonance-Raman spectrum excited by the 488 nm Ar⁺ laser line. Bands centred at 153, 170, 264 and 304 cm^?1 have been assigned as ν₃, 2ν₂, ν₁+ν₃ and 2ν₃(Σ⁺) respectively. The remaining structure between the nν₁ lines has been assigned as due to combinations of these lines with the lattice vibrations of the CsI crystal.     

Two-color excitation of NO in a supersonic free jet. Autoionization of high rydberg states

High Rydberg states of NO above the ionization limit have been measured for the isolated molecule in a supersonic free jet by two-color multiphoton ionization. Three Rydberg series (ns, np and nf) were identified, which appeared by rotational and the vibrational autoionization. The rotational structures of the 13s(υ = 1), 13p(υ = 1) and 12f(υ = 1) states have been analyzed in detail. The fluorescence dip spectra for the intermediate A²Σ⁺(3sσ) state have been measured simultaneously and the cross sections of the one-photon absorption to the high Rydberg states from the A²Σ⁺(υ = 1) state have been determined.     

Spectra and structure of organophosphorus compounds: XVII. Infrared and Raman spectra. vibrational assignment and barriers to internal rotation for t-butylphosphine

The infrared spectra of gaseous and solid tertiary-butylphosphine, [(CH₃)₃CPH₂], have been recorded from 50 cm^?1 to 3500 cm^?1. The Raman spectra of gaseous, liquid and solid (CH₃)₃CPH₂ have been recorded from 10 to 3500 cm^?1. A vibrational assignment of the 42 normal modes has been made. A harmonic approximation of the methyl torsional barrier from observed transitions in the solid state gave a result of 4.22 kcal mol^?1 and 3.81 kcal mol^?1 in the gaseous state. Hot band transitions for the phosphino torsional mode have been observed. The potential function for internal rotation about the C-P bond has been calculated. The two potential constants were determined to be: V₃ = 2.79 ± 0.01 kcal mol^?1 and V₆ = 0.07 ± 0.01 kcal mol^?1.     

Synthesis of (2-hydroxo-5-chlorophenylaminoisonitrosoacetyl)phenyl ligands and their complexes: Spectral,thermal and solvent-extraction studies

Four different types of new ligands Ar[COC(NOH)R] _n (Ar=biphenyl, n = 1 H₂L¹; Ar=biphenyl, n = 2 H₄L²; Ar=diphenylmethane, n = 1 H₂L³; Ar=diphenylmethane, n = 2 H₄L⁴; R=2-amino-4-chlorophenol in all ligands) have been obtained from 1 equivalent of chloroketooximes Ar[COC(NOH)Cl] _n (HL¹-H₂L⁴) and 1 equivalent of 2-amino-4-chlorophenol (for H₂L¹ and H₂L³) or 2 equivalent of 2-amino-4-chlorophenol (for H₄L² and H₄L⁴). (Mononuclear or binuclear cobalt(II), nickel(II), copper(II) and zinc(II) complexes were synthesized with these ligands.) These compounds have been characterized by elemental analyses, AAS, infra-red spectra and magnetic susceptibility measurements. The ligands have been further characterized by ¹H NMR. The results suggest that the dinuclear complexes of H₂L¹ and H₂L³ have a metal:ligand ratio of 1:2; the mononuclear complexes of H₄L² and H₄L⁴ have a metal:ligand ratio of 1:1 and dinuclear complexes H₄L² and H₄L⁴ have a metal:ligand ratio of 2:1. The binding properties of the ligands towards selected transition metal ions (Mn^II, Co^II, Ni^II, Cu^II, Zn^II, Pb^II, Cd^II, Hg^II) have been established by extraction experiments. The ligands show strong binding ability towards mercury(II) ion. In addition, the thermal decomposition of some complexes is studied in nitrogen atmosphere.