Vinyl Hydrogen Research Articles

Functionalization of poly(vinyl alcohol) by addition of methacryloyl groups: characterization by FTIR and NMR and optimization of reaction conditions by RSM

AbstractThe modification of poly(vinyl alcohol) (PVA) with glycidyl methacrylate (GMA) in DMSO catalyzed by TEMED is reported in this paper. PVA was dissolved in DMSO and reacted with GMA at 30 ºC in a closed vessel under N2 gas bubbling for 24 hours. The reaction was characterized by FTIR and NMR (1H, 13C/DEPT and HETCOR) spectroscopies. The reaction occurs by transesterification through the insertion of methacryloyl groups into PVA chains and probably with the formation of glycidol as a by-product. The degree of substitution (DS) that represents the number of methacryloyl groups inserted was determined through 1H NMR spectra based on the ratio between the averaged area due to the vinyl hydrogen from methacryloyl groups at δ̣ 5.6 ppm and δ 6.0 ppm and the total area of the vinyl hydrogen and hydroxyl hydrogen of PVA. By use of response surface methodology the experimental conditions were optimized. The optimum conditions were 62 ºC with a reaction time of 6 hours. In these optimized conditions, the reactions using the molar ratios [-OH(PVA)/GMA] equal to 1/0.10, 1/0.25, 1/0.50, 1/0.75 and 1/1 were investigated. The response surface was based on the model DS= −19.70 + 6.09x10−1T +1.93 t − 3.89x10−3 T2 − 5.21x10−2t2 − 2.14x10−2 T * t, where T is the temperature (°C) and t the reaction time (hours). This model explained 99.20 % of the 99.64 % explainable statistical data. Using the optimized conditions, it is possible to produce a desired modified PVA, (or PVA-Ma), because DS raises linearly to the ratio [-OH(PVA)/GMA] up to 25 mol-% and the respective yield ranged from 83 to 92 %. It is difficult to obtain more than 50 mol-% substitution of PVA hydroxyl by methacryloyl groups even in these optimized conditions due to increased steric hindrance by the large number of the methacryloyl groups inserted into PVA.

Highly Activated Vinyl Hydrogen in a Significantly Twisted Styrene

The novel example of a vinylic hydrogen more reactive than a benzylic hydrogen was found by treatment of a twisted styrene derivative with a strong base followed by D(2)O quenching. In this paper, the full details of the examples of the highly activated vinyl hydrogens in twisted styrene derivatives are described, with a discussion on the correlation between the reactivity of the vinyl hydrogens and the magnitude of the twist. The highly reactive vinyl hydrogens could be rationalized by considering the novel orbital interaction between the pi(*) orbital of the benzene ring and the pi(*) orbital of the vinylic C-H bond in the twisted styrene derivatives.

Synthesis and Use of Probes to Investigate the Cryptoregiochemistry of the First Animal Acetylenase

Thaumetopoea pityocampa pheromone glands contain an unusual Delta(11) acetylenase that produces an alkynoic fatty acid intermediate in the sex pheromone biosynthetic pathway of this species. In this article, we describe the synthesis and use of the deuterated (Z)-11-hexadecenoic acid probes required to decipher the cryptoregiochemistry of this enzyme. The label in the olefinic bonds was introduced by Wittig reaction between the appropriate deuterated reagents. Besides the vinyl deuterium atoms, for reliable GC-MS analyses these compounds bear a tetradeuterium tag, which was introduced by deuteration of an alkyne intermediate in the presence of the Wilkinson catalyst. Pheromone gland metabolization studies of these probes provided experimental evidence that the transformation of (Z)-11-hexadecenoic acid into 11-hexadecynoic acid by the Delta(11) acetylenase takes place by a stepwise mechanism, in which a significant perturbation of the strong vinyl C11-H bond occurs prior to a fast elimination of the vinyl hydrogen at C-12.

One‐Pot β‐Substitution of Enones with Alkyl Groups to β‐Alkyl Enones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structure and Chiral Recognition Ability of endo-3-Benzamidonorborn-5-ene-2-carboxylic Acid

Abstract The absolute configuration of endo-3-benzamidonorborn-5-ene-2-carboxylic acid was determined by X-ray single crystal analysis of the diastereomeric salt with cis-2-(benzylamino)cyclohexylmethanol. It was demonstrated that the CH–π interaction between the vinylic hydrogen atom of the acid and the aromatic ring of the amine worked as an additional interaction for the stabilization of the structure formed by the hydrogen bond network. The chiral recognition ability was studied using a 1H NMR titration technique and the intermolecular interactions were discussed based on the results of its saturated counterpart, endo-3-benzamidonorbornane-2-carboxylic acid.

Prosthetic Heme Modification during Halide Ion Oxidation. Demonstration of Chloride Oxidation by Horseradish Peroxidase

Myeloperoxidase (MPO), eosinophil peroxidase (EPO), and chloroperoxidase can oxidize iodide, bromide, and chloride, but most peroxidases, including the prototypical horseradish peroxidase (HRP), reportedly only oxidize iodide and, in some cases, bromide. We report here that incubation of HRP with Br(-) and H(2)O(2) at acidic pH results in both bromination of monochlorodimedone and modification of the heme group. Mass spectrometry indicates that the heme 2- and 4-vinyl groups are modified by either replacement of a vinyl hydrogen by a bromide or addition of HOBr to give a bromohydrin. These reactions do not occur if protein-free heme and Br(-) are co-incubated with H(2)O(2) or if the HRP reaction is carried out at pH 7. Surprisingly, similar prosthetic heme modifications occur in incubations of HRP with H(2)O(2) and Cl(-). A mechanism is proposed involving oxidation of Br(-) or Cl(-) to give HOBr or HOCl, respectively, followed by addition to a vinyl group. In the reaction with Cl(-), a meso-chloro heme adduct is also formed. This first demonstration of Cl(-) oxidation by HRP, and the finding that prosthetic heme modification occurs when Br(-) or Cl(-) is oxidized in the absence of a cosubstrate, show that only modest tuning is required to achieve the unique chloride oxidation activity of MPO and EPO. The results raise the question of how the prosthetic hemes of MPO and EPO, whose function is to produce oxidized halide species, escape modification.

Facile Preparation of the Water-Soluble Singlet Oxygen Traps Anthracene-9,10-divinylsulfonate (AVS) and Anthracene-9,10-diethylsulfonate (AES) via a Heck Reaction with Vinylsulfonate

An easy 2-step method for the synthesis of the water-soluble singlet oxygen trap AES has been developed. The method is based on a novel Heck reaction with sodium vinylsulfonate followed by vinyl hydrogenation. It is shownthat the Heck product AVS is also suitable as a water-soluble and colored singlet oxygen trap that allows singlet oxygen to be detected specifically and simply by visual inspection. The cumulative amount of 1 O 2 generated into the solution can be determined unambiguously by measuring the concentration of the endoperoxides AVSO 2 or AESO 2 by HPLC or by 1 H NMR.

One-pot β-substitution of enones with alkyl groups to β-alkyl enones

Vinylic hydrogens at the beta-position of enones were effectively substituted with alkyl groups in a one-pot procedure to afford beta-alkyl enones in good to high isolated yields by conjugate addition of higher-order dialkyl cyanocuprates to enones, followed by a reaction with N-tert-butylbenzenesulfinimidoyl chloride at -78 degree C.

A characterisation of the complex vinyl fluoride⋯hydrogen fluoride by rotational spectroscopy and ab initio calculations

Combined use of rotational spectroscopy and ab initio calculations at the MP2/6-311++G(d,p) level of theory shows that the complex formed between vinyl fluoride and hydrogen fluoride has a planar geometry in which HF forms a hydrogen bond to the F atom of vinyl fluoride. With ϕ = the angle CF⋯H = 121.4° assumed from the ab initio calculation, the distance r(FH) = 1.892(14) Å and the angular deviation θ = 18.7(15)° of the F⋯H–F nuclei from collinearity were obtained by fitting the principal moments of inertia of the two isotopomers C 2H 3F⋯HF and C 2H 3F⋯DF investigated.

Vibrational analysis, conformational stability, force constants, barriers to internal rotations, RHF, MP2 and DFT calculations of trans,trans‐2,4‐hexadiene

AbstractSix conformers are proposed for the trans,trans‐2,4‐hexadiene (TTHD) molecule. Utilizing the 6–31G(d) and 6–311 + G(d) basis sets at the levels of RHF, MP2 with full electron correlation and DFT‐B3LYP, five conformers are found to be transition states, due to the calculated imaginary wavenumber(s). Accordingly, the totally symmetric TTT conformer where the two methyl groups are staggered to all trans vinylic hydrogen's (C2h symmetry) is the stable conformer in the gaseous, liquid and crystalline phases. Aided by MP2(full)/6–311 + G(d) geometric parameters, a chosen value of the kinetic parameter F = 6.11284856 was determined. Utilizing the observed band at 148 cm−1 in the far‐infrared spectrum of the gas, a value of 1.41 ± 0.06 kcal mol−1 was obtained for the C3v internal rotor (V3), compared with 1.83 ± 0.07 kcal mol−1 predicted from a potential energy surface scan (1 kcal = 4.184 kJ). Aided by normal coordinate analysis and quantum chemistry (QC) calculations, the scaled quantum mechanical (SQM) force field was obtained employing five scaling factors for different types of vibrational motions. The scaled vibrational wavenumbers from both MP2(full) and B3LYP levels using the 6–31G(d) basis set provides an excellent approach to the observed fundamentals in either infrared or Raman spectra of the TTT conformer. Thus, confident vibrational assignments and potential energy distributions (PEDs) were provided for all fundamental modes of the TTT conformer. Moreover, the conformational stabilities, structural parameters, rotational constants, infrared intensities and Raman scattering activities are also reported. These results are discussed and compared with the experimentally determined values for some related conjugate systems when appropriate. Copyright © 2004 John Wiley & Sons, Ltd.

Specific adhesion model for bonding hot-melt polyamides to vinyl

Hot-melt polyamides are an important market for the dimer acid made from the tall oil fatty acids liberated during the Kraft pulping process. These polyamides bond well to many substrates, but not to polyvinyl chloride (PVC), commonly called vinyl. Dimer-based polyamides made from secondary amines such as piperazine bond well to vinyl. No model for this unique adhesion has been proposed even though many commercial adhesives and other patents have utilized this feature of dimer-based polyamides. This paper examines the validity of models based on mechanical interlock, rheological properties, solubility parameters, and acid–base interactions. Available data are consistent with the acid–base model, which depends on the availability of tertiary amides made from secondary amine to bond to the vinyl hydrogen in contrast to the strong internal polyamide hydrogen bonding of secondary amides made from primary amines. Poly(ester-amides) with a similar proton acceptor ability also bond to vinyl.

Unique Reactivity of Twisted 1,3‐Diene

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium catalyzed transformations of monoterpenes: stereoselective deuteriation and oxidative dimerization of camphene

Camphene undergoes a highly regio and stereoselective palladium catalyzed deuteriation in deuteriated acetic acid solutions of Pd(OAc) 2. NMR reveals that an outward oriented vinylic hydrogen is selectively exchanged for 2H, resulting in 90% camphene- d 1 (ca. 100% stereoselectivity) and 10% camphene- d 2 at 75% conversion of camphene (6 h, 25 °C). Neither π-allyl nor π-olefin palladium complexes are formed in detectable concentrations during the reaction, whereas palladium hydride (singlet at −6.86 ppm) and palladium deuteride (singlet at −6.78 ppm) intermediates have been detected by 1H and 2H NMR, respectively. At higher temperature, oxidative coupling of camphene readily occurs giving the ( E, E)-diene, i.e., bis(3,3-dimethyl-2-norbornylidene)ethane, which formally originates by abstracting the outward oriented vinylic hydrogens and coupling the resulting fragments of two camphene molecules. The reaction is catalytic at palladium in the Pd(OAc) 2–LiNO 3(cat)–O 2 and Pd(OAc) 2–benzoquinone systems. Similar mechanisms for the deuteriation and oxidative coupling of camphene are proposed, which involve the formation of σ-vinyl palladium hydride intermediates. No deuteriation neither oxidative coupling of limonene, myrcene and β-pinene were observed under the same conditions.

A First-Principles Analysis of Acetylene Hydrogenation over Pd(111)

Nonlocal gradient-corrected periodic density functional theory (DFT) calculations have been carried out to examine the hydrogenation of acetylene over Pd(111). The binding energies of acetylene, atomic hydrogen, vinyl, and ethylene at 25% (33%) coverage were computed to be −172 (−136), −260 (−248), −274 (−235), and −82 (−62) kJ/mol, respectively. The reaction energy for acetylene hydrogenation to vinyl over Pd(111) was found to be −26 (−43) kJ/mol at 25% (33%) coverage. The overall reaction energy for vinyl hydrogenation to ethylene was calculated to be −58 and −731 kJ/mol at 25% and 33% coverages, respectively. Acetylene hydrogenation to vinyl is therefore less exothermic than vinyl hydrogenation to ethylene. The intrinsic activation barrier for the addition of atomic hydrogen to acetylene over Pd was calculated to be +66 kJ/mol at 25% coverage and +50 kJ/mol at 33% coverage. The barrier for vinyl hydrogenation to form ethylene over Pd(111) at 25% coverage was computed at +85 kJ/mol while that at 33% cov...

1,3-Cycloaddition of pyrazole to the allenylidene ligand in [Re{CCCPh 2}(CO) 2{MeC(CH 2PPh 2) 3}] +

The reaction of the allenylidene complex [Re{CCCPh 2}(CO) 2(triphos)]OTf ( 1) (triphos=MeC(CH 2PPh 2) 3; OTf= −OSO 2CF 3) with pyrazole gave the 1,2,3-diheterocyclization product [Re{CCHCPh 2(N 2C 3H) 3}(CO) 2(triphos)]Y (Y=OTf, 2OTF; Y=BPh 4, 2BPh 4 ). The molecular structure of this complex was determined by a single-crystal X-ray analysis. Treatment of 2 with sodium methoxide gave the pyrazolyl-functionalized alkynyl derivative [Re{CCCPh 2(N 2C 3H 3)}(CO) 2(triphos)] ( 3) via selective deprotonation of the vinylic hydrogen, followed by back opening of the metal-bound heterocycle. Protonation of 3 with triflic acid in dichloromethane re-generated 1 and free pyrazole. The overall result of this deprotonation/protonation sequence allowed us to propose a reliable mechanism for the formation of the 1,2,3-diheterocyclization product 2OTf.

捻れた１，３−ジエンが示すユニークな反応性

We have recently found the novel character of twisted 1, 3-dienes in two types of reactions; one is photosensitized oxygenation and another is anion formation with base. In the former reaction, the selective allene formation resulting from the ene reaction of the vinyl hydrogen rather than the allyl hydrogen was disclosed. On the basis of MM and MO calculations, the abnormally higher reactivity of the vinyl hydrogen would be rationalized by considering the σ-π orbital interaction between the vinyl C-H bond and another double bond. Diastereoselective allene formation resulting from the chiral projection from sp3 carbon into an allene was also realized. In the latter reaction, the selective vinyl anion formation rather than benzylic anion formation was observed in the twisted styrene derivatives. In this paper, we will describe our recent study on twisted 1, 3-dienes in detail, in addition to the recent topics by another research groups.

Activation of alkenes and H2 by [Fe]-H2ase model complexes.

The established ability of the Fe(II) bridging hydride species (micro-H)(micro-pdt)[Fe(CO)2(PMe3)]2+, 1-H+, to take-up and heterolytically activate dihydrogen, resulting in H/D scrambling of H2/D2 and H2/D2O mixtures (Zhao et al. Inorg. Chem. 2002, 41, 3917) has prompted a study of simultaneous alkene/H2 activation by such [Fe]H2ase model complexes. That the required photolysis produced an open site was substantiated by substitution of CO in 1-H+ by CH3CN with formation of structurally characterized [(micro-H)(micro-pdt)[Fe(CO)2(PMe3)][Fe(CO)(CH3CN)(PMe3)]]+[PF6]-. Under similar photolytic conditions, H/D exchange reactions between D2 and terminal alkenes (ethylene, propene and 1-butene), but not bulkier alkenes such as 2-butene or cyclohexene, were catalyzed by 1-H+ and the edt (SCH2CH2S) analogue, 2-H+. Substantial regioselectivity for H/D exchange at the internal vinylic hydrogen was observed. The extent to which the olefins were deuterium enriched vs deuterated was catalyst dependent. The stabilizing effect of the binuclear chelating ligands, SCH2CH2CH2S, pdt, and SCH2CH2S, edt, is required for the activity of binuclear catalysts, as the mono-dentate micro-SEt analogue decomposed to inactive products under the photolytic conditions of the catalysis. Reactions of 1 and 2 with EtOSO2CF3 yielded the S-alkylated products, [(micro-SCH2CH2CH2SEt)[Fe(CO)2(PMe3)]2]+[SO3CF3]- (1-Et+), and 2-Et+, rather than micro-C2H5 analogues to the micro-H of 1-H+. The stability and lack of reactivity toward H2 of 1-Et+ and 2-Et+, indicates they are not on the reaction path of the olefin/D2 H/D exchange process. A mechanism with olefin binding to an open site created by CO loss and formation of an Fe-(CH2CHDR) intermediate is indicated. A likely role of a binuclear chelate effect is implicated for the unique S-XXX-S cofactor in the active site of [Fe]H2ase.

Phase behavior of binary polybutadiene copolymer mixtures as an example of weakly interacting polymers

Binary blends of statistical polybutadiene copolymers of different vinyl content and molar volume were explored by small-angle neutron scattering. These samples represent the most simple class of statistical copolymer mixtures. In spite of this simplicity, changes in vinyl content, molar volume, and deuterium and hydrogen content of the chains give rise to strong effects; phase separation occurs from minus 230 °C to more than plus 200 °C and can even reverse from an enthalpically driven one at low temperatures to an entropically driven one at high temperatures. The entropic and enthalpic terms of the Flory–Huggins parameter as determined from the experiment are in excellent agreement with lattice cluster theory calculations.

Gas-phase ozonolysis of alkenes: formation of OH from anti carbonyl oxides.

Gas-phase ozone-alkene reactions are known to produce the hydroxyl radical (OH) in high yields. Most mechanistic studies to date have focused on the role of syn carbonyl oxides; however, OH production from ethene ozonolysis indicates a second, poorly understood OH-forming channel, which may contribute to OH production in the ozonolysis of substituted alkenes as well. Using laser-induced fluorescence, we have measured OH and OD yields from the ozonolysis of two partially deuterated alkenes, cis- and trans-3-hexene-3,4-d2. OD is formed from both alkenes, indicating a pathway of hydroxyl-radical formation involving vinylic hydrogens, accounting for one-third of total OH formation from cis-3-hexene. The lack of a significant kinetic isotope effect suggests this pathway is the "hot acid" channel, arising from rearrangement of anti carbonyl oxides. Measured yields also allow for the estimation of syn:anti carbonyl oxide ratios, approximately 50:50 for trans-3-hexene and approximately 20:80 for cis-3-hexene, qualitatively consistent with our understanding of ozonide decomposition pathways.

Simple entry to 3'-substituted analogues of anti-HIV agent stavudine based on an anionic O --> C stannyl migration.

Reaction of 5'-O-protected derivatives of the anti-HIV agent stavudine (d4T) with LTMP was investigated with the aim to lithiate the vinylic hydrogens (H-3' and H-2'). When the lithiation of the 5'-O-tert-butyldiphenylsilyl derivative 5 was carried out in the presence of HMPA, an anionic silyl migration took place to give the 3'-C-silylated product 4a. The stannyl version of this reaction was found to be also possible, which has disclosed a highly simple entry to the d4T analogues variously substituted at the 3'-position by manipulating the 3'-C-stannyl d4T as a common intermediate.