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1.
Carbenes are reactive molecules of the form R1? C?? R2 that play a role in topics ranging from organic synthesis to gas‐phase oxidation chemistry. We report the first experimental structure determination of dihydroxycarbene (HO? C?? OH), one of the smallest stable singlet carbenes, using a combination of microwave rotational spectroscopy and high‐level coupled‐cluster calculations. The semi‐experimental equilibrium structure derived from five isotopic variants of HO? C?? OH contains two very short CO single bonds (ca. 1.32 Å). Detection of HO? C?? OH in the gas phase firmly establishes that it is stable to isomerization, yet it has been underrepresented in discussions of the CH2O2 chemical system and its atmospherically relevant isomers: formic acid and the Criegee intermediate CH2OO.  相似文献   

2.
Reactions of bis(acetylacetonato)aluminum(III)‐di‐μ‐isopropoxo‐di‐isopropoxo aluminum(III), [(CH3COCHCOCH3)2Al(μ‐OPri)2Al(OPri)2] with aminoalcohols, (HO R NR1R2) in 1:1 and 1:2 molar ratios in refluxing anhydrous benzene yielded binuclear complexes of the types [(CH3COCHCOCH3)2Al(μ‐OPri)2Al(O R NR1R2)(OPri)] and [(CH3COCHCOCH3)2Al(μ‐OPri)2Al(O R NR1R2)2] (R   (CH2)3 , R1 = R2 = H; R =  CH2C(CH3)2 , R1 = R2 = H; R =  (CH2)2 , R1 = H, R2 =  CH3; and R   (CH2)2 , R1 = R2 = CH3), respectively. All these compounds are soluble in common organic solvents and exhibit sharp melting points. Molecular weight determinations reveal their binuclear nature in refluxing benzene. Plausible structures have been proposed on the basis of elemental analysis, molecular weight measurements, IR, NMR (1H, 13C, and 27Al), and FAB mass spectral studies. 27Al NMR spectra show the presence of both five‐ and six‐coordinated aluminum sites. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:518–522, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10184  相似文献   

3.
A comparison of the OH chemical shifts for 1‐mono‐, 4‐mono‐, and 1,4‐diethynylated and 1,4‐buta‐1,3‐diynylated glucopyranoses with those of β‐D ‐glucopyranose ( 1 ) identified characteristic increments for the OH (downfield) shifts of the alkynylated glucopyranoses in (D6)DMSO solution. For ethynylated derivatives, the increments vary from 0.05 ppm for HO C(6) (replacement of HO C(1) by an axial ethynyl group) to 0.5 ppm for HO C(2) (replacement of HO C(1) by an equatorial ethynyl group). The increments for buta‐1,3‐diynylated derivatives are larger, and vary from 0.1 to 0.7 ppm. The influence on the shift for vicinal OH groups is stronger for such a substitution at C(1) rather than at C(4).  相似文献   

4.
Surface frustrated Lewis pairs (SFLPs) have been implicated in the gas‐phase heterogeneous (photo)catalytic hydrogenation of CO2 to CO and CH3OH by In2O3?x(OH)y. A key step in the reaction pathway is envisioned to be the heterolysis of H2 on a proximal Lewis acid–Lewis base pair, the SFLP, the chemistry of which is described as In???In‐OH + H2 → In‐OH2+???In‐H?. The product of the heterolysis, thought to be a protonated hydroxide Lewis base In‐OH2+ and a hydride coordinated Lewis acid In‐H?, can react with CO2 to form either CO or CH3OH. While the experimental and theoretical evidence is compelling for heterolysis of H2 on the SFLP, all conclusions derive from indirect proof, and direct observation remains lacking. Unexpectedly, we have discovered rhombohedral In2O3?x(OH)y can enable dissociation of H2 at room temperature, which allows its direct observation by several analytical techniques. The collected analytical results lean towards the heterolysis rather than the homolysis reaction pathway.  相似文献   

5.
Aqueous‐phase dissociation constants (Ka) for the conjugate acids of a series of 2‐azidoethanamine bases: R1N(R2)CH2CH2N3 ( 1 , R1 = CH3, R2 = H; 2 , R1 = CH3, R2 = CH3; 3 , R1 = CH2CH3, R2 = CH2CH3; 4 , R1/R2 =  CH2CH2CH2CH2 ; 5 , R1/R2 =  CH2CH2OCH2CH2 ; 6 , R1 = CH2CH3, R2 = CH2CH2N3) were measured and found to fall between those for analogous unfunctionalized and cyano‐functionalized ethanamines. To explore the possibility of a relationship existing between the constants and molecular geometry, a theoretically based study was conducted. In it, the Gibbs free energies of aqueous‐phase (equilibrium) conformers of the bases and their conjugate acids were determined via a density functional theory/polarizable continuum model method. The results indicate that an attractive interaction between the amine and azide groups that underlies the lowest‐energy gas‐phase conformer of 2 is negated in an aqueous environment by solvent–solute interactions. The magnitudes of the free energy changes of solvation and −TS (entropic) energies of the conformers of the 2‐azidoethanamines and their conjugate acids are observed to correlate with the magnitude of the separation between the conformers' amine and azide groups. However, those correlations are not by themselves sufficient to predict the relative free energies of a molecule's conformers in an aqueous environment. That insufficiency is due to the influence of the correlations being mitigated by three other parameters that arise within the thermodynamic framework employed to compute the observable. The nature of those parameters is discussed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010  相似文献   

6.
Correlated ab initio molecular orbital, DFT, QCISD, G3MP2, and QCISD(T) calculations have been used to investigate the geometries, energetics, and mechanisms governing the insertion reactions of 1CH2 into O H and N H bonds of water and ammonia, respectively, in gas phase adopting 6‐311++g(d, p) basis set. It is found that 1CH2 reacts with water and ammonia to produce the ylide‐like intermediates H2C OH2 and H2C NH3, which in turn undergo 1,2‐hydrogen shift to produce methanol and methylamine, respectively. Results obtained indicate that in the gas phase, the ylides and the transition states are located below the reactants' energy levels. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010  相似文献   

7.
The stable cationic iridacyclopentenylidene [TpMe2Ir(CHC(Me)C(Me)C H2(NCMe)]PF6 ( A ; TpMe2=hydrotris(3,5‐dimethylpyrazolyl)borate) has been obtained by α‐hydride abstraction from the iridacyclopent‐2‐ene [TpMe2Ir(CH2C(Me)C(Me)C H2)(NCMe)]. Complex A exhibits Brønsted–Lowry acidity at the Ir CH2 and proximal (relative to Ir CH2) methyl sites. The coordination of an extra molecule of acetonitrile to the iridium center initiates the reversible isomerization of the chelating carbon chain of A to the monodentate butadienyl ligand of complex [TpMe2Ir(CHC(Me)C(Me)CH2)(NCMe)2]PF6, which is capable to engage in a water‐promoted C C coupling with the MeCN co‐ligands. The product is an aesthetically appealing bicyclic structure that resembles the hydrocarbon barrelene.  相似文献   

8.
An intermolecular C(sp3) H amination using a Pd0/PAr3 catalyst was developed. The reaction begins with oxidative addition of R2N OBz to a Pd0/PAr3 catalyst and subsequent cleavage of a C(sp3) H bond by the generated Pd NR2 intermediate. The catalytic cycle proceeds without the need for external oxidants in a similar manner to the extensively studied palladium(0)‐catalyzed C H arylation reactions. The electron‐deficient triarylphosphine ligand is crucial for this C(sp3) H amination reaction to occur.  相似文献   

9.
Urethane reactions of cycloaliphatic and aromatic diisocyanates with hydroxy‐terminated fluoropolyethers (FPEs) of various molecular weights and structure, at NCO : OH = 2, have been studied by monitoring, by IR analysis, the rate of decrease in NCO absorbance at 2264–2268 cm−1. Different diisocyanates have been tested, among them the following: 4,4′‐dicyclohexylmethane diisocyanate (H12MDI); 5‐isocyanato‐1,3,3‐trimethylcyclohexylmethyl isocyanate or isophorone diisocyanate (IPDI); 2,4‐toluene diisocyanate (TDI). Ethyl acetate (EA), methyl isobutyl ketone (MIBK), and hexafluoroxylene (HFX) have been used as solvents in presence of dibutyltin dilaurate (DBTDL) or 1,4‐diazabicyclo[2.2.2]octane (DABCO) as catalysts. These reactions gave rise to NCO‐end‐capped FPE–oligourethanes. Preliminary solubility tests for HO‐terminated FPEs in various solvents made it possible to select proper candidates for carrying out reaction in homogeneous conditions at high concentrations of reagents (30–50% w/w). The second‐order kinetic mechanism was shown to be valid. Positive deviations from linearity for the second‐order kinetics around 40–80% conversion, found for most of the FPE diols, were attributed to the autocatalysis of the isocyanate–hydroxyl reaction by the arising urethane groups. Uncatalyzed reactions with cycloaliphatic diisocyanates are very slow at 40°C. The tertiary amine DABCO is a much less effective catalyst than DBTDL. FPEs having terminal OH groups separated from the perfluorinated main molecular chain by  (OCH2CH2)n segments (n = 1–2) are generally more reactive than FPEs with end  CH2OH groups. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 557–570, 1999  相似文献   

10.
A range of 4‐monosubstituted and 2,4‐disubstituted 1H‐imidazoles and 1H‐imidazole‐1‐ethanols (R C(4): CH2CH2Ph, CHOHCH2Ph, Ph, or Me; R C(2): CH2OH, CHOHCH2OH, CN, or CH2NHAc) were prepared and tested as inhibitors of α‐ and β‐glucosidases and of a β‐galactosidase. A new access to 4‐(2‐phenylethyl)‐1H‐imidazoles starting from 4‐phenylbutan‐1‐ol was elaborated. The strongest inhibitors are the 2‐substituted 4‐(2‐phenylethyl)‐1H‐imidazoles 24a and 26a (R C(2): CH2OH and CHOHCH2OH) and the 2‐phenylethanol 34 . They inhibit the β‐galactosidase from bovine liver and the β‐glucosidase from Caldocellum saccharolyticum with inhibition constants in the micromolar range, but do not inhibit the α‐glucosidase from brewer's yeast.  相似文献   

11.
Summary: The laser irradiation at 193 nm of a gaseous mixture of carbon disulfide and ethene induces the copolymerization of both compounds and affords the chemical vapour deposition of a C/S/H polymer, the composition of which indicates the reaction between two to three CS2 molecules and one C2H4 molecule. Polymer structure is interpreted on the basis of X‐ray photoelectron and FT‐IR spectra as consisting of >CS, >CC<,  CH2 CH2 , (CC)SnC4 − n,  C (CS) S ,  S (CS) S , and C S S C configurations. The gas‐phase copolymerization of carbon disulfide and ethene represents the first example of such a reaction between carbon disulfide and a common monomer.

Scheme showing the expected reaction of excited CS2 molecules with other CS2 molecules to form dimers, which then react with another CS2 molecule or add to ethene.  相似文献   


12.
In view of the prominent role of the 1H‐indol‐3‐yl side chain of tryptophan in peptides and proteins, it is important to have the appropriately protected homologs H‐β2 HTrp OH and H‐β3 HTrp OH (Fig.) available for incorporation in β‐peptides. The β2‐HTrp building block is especially important, because β2‐amino acid residues cause β‐peptide chains to fold to the unusual 12/10 helix or to a hairpin turn. The preparation of Fmoc and Z β2‐HTrp(Boc) OH by Curtius degradation (Scheme 1) of a succinic acid derivative is described (Schemes 2–4). To this end, the (S)‐4‐isopropyl‐3‐[(N‐Boc‐indol‐3‐yl)propionyl]‐1,3‐oxazolidin‐2‐one enolate is alkylated with Br CH2CO2Bn (Scheme 3). Subsequent hydrogenolysis, Curtius degradation, and removal of the Evans auxiliary group gives the desired derivatives of (R)‐H β2‐HTrp OH (Scheme 4). Since the (R)‐form of the auxiliary is also available, access to (S)‐β2‐HTrp‐containing β‐peptides is provided as well.  相似文献   

13.
The reactions of 3,3′‐diaminobenzidine with 1,12‐dodecanediol in 1 : 1–1:3 molar ratios in the presence of RuCl2(PPh3)3 catalyst give poly(alkylenebenzimidazole), [ (CH2)11 O (CH2)11 Im / (CH2)10 Im ]n (Im: 5,5′‐dibenzimidazole‐2,2′‐diyl) (Ia‐Id) in 71–92% yields. The relative ratio between the [(CH2)11 O (CH2)11 Im ] unit (A) and the [‐ (CH2)10 Im ] unit (B) in the polymer chain varies depending on the ratio of the substrates used. The polymer Ia obtained from the 1 : 3 reaction contains these structural units in a 98 : 2 ratio. The polymers are soluble in polar solvents such as DMF (N,N‐dimethylformamide), DMSO (dimethyl sulfoxide), and NMP (N‐methyl‐2‐pyrrolidone) and have molecular weights Mn (Mw) of 4,200–4,800 (4,800–6,500) by GPC (polystyrene standard). The polymerization of the diol and 3,3′‐diaminobenzidine in higher molar ratios leads to partial cross‐linking of the resulting polymers Ie and If via condensation of imidazole NH group with CH2OH group. Similar reactions of 3,3′‐diaminobenzidine with α,ω‐diols, HO(CH2)mOH (m = 4–10), in a 1 : 3 molar ratio give the polymers containing [ (CH2)m−1 O (CH2) m−1 Im ] and [ (CH2) m−2 Im ] units with partial cross‐linked structures. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1383–1392, 1999  相似文献   

14.
Cyanoacetaldehyde (NC? CH2CH?O) and its isomer, cyanovinylalcohol (NC? CH?CH? OH), as possible components of the interstellar medium, comets, or planetary atmospheres, exist in equilibrium in the gas phase, although the latter compound is very much in the minority (2 %). The recording and analysis of the gas‐phase infrared spectrum of the former compound within the 4000–500 cm?1 spectroscopic range and the potential presence of the latter isomer, which could be vital for their detection in these media, are reported. CCSD(T) and G4 high‐level ab initio methods, as well as density functional theory calculations, predict the existence of two stable rotamers of cyanoacetaldehyde. The global minimum has a structure with an unusual O‐C‐C‐C dihedral angle (150°) that falls between the antiperiplanar (180°) and anticlinal forms (120°). The second rotamer, which is about 4.0 kJ mol?1 less stable in terms of free energy, has a planar structure that corresponds to the synperiplanar form (O‐C‐C‐C dihedral angle: 0°). The absorption vibrational bands of the two aldehyde rotamers that are present in the mixture lead to a spectrum with a very complex structure in the region of deformation movements, in which several low‐intensity bands overlap. A complete and unambiguous assignment of the experimental spectrum has been achieved by using the calculated harmonic and anharmonic vibrational frequencies.  相似文献   

15.
Methoxydimethylsilane and chlorodimethylsilane‐terminated telechelic polyoctenomer oligomers (POCT) have been prepared by acyclic diene metathesis (ADMET) chemistry using Grubbs' ruthenium Ru(Cl2)(CHPh)(PCy3)2 [Ru] or Schrock's molybdenum Mo(CH CMe2Ph)(N 2,6 C6H3i Pr2)(OCMe(CF3)2)2 [Mo] catalysts. These macromolecules have been characterized by FTIR, 1H‐, 13C‐, and 29Si‐NMR spectroscopy. The molecular weight distributions of these polymers have been determined by GPC and vapor pressure osmometry (VPO). The number‐average molecular weight (Mn) values of the telechelomers are dictated by the initial ratio of the monomer to the chain limiter. The termini of these oligomers (Mn = 2000) can undergo a condensation reaction with hydroxy‐terminated poly(dimethylsiloxane) (PDMS) macromonomer (Mn = 3300) [HO Si(CH3)2 O { Si(CH3)2O }x  Si(CH3)3], producing an ABA‐type block copolymer, as follows: (CH3)3SiO [ Si(CH3)2O ]x [ CHCH (CH2)6 ]y [ OSi(CH3)2 ]x OSi(CH3)3. The block copolymers were characterized by 1H‐ and 13C‐NMR spectroscopy, VPO, and GPC, as well as elemental analysis, and were determined by VPO to have a Mn of 8600. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 849–856, 1999  相似文献   

16.
Several fluorinated allylic ethers, thioethers and diethers have been prepared in excellent yields by phase transfer catalysis (CTP). The used halogenated compounds are allyl chloride and bromide, p-chloromethylstyrene. The used fluorinated alcohols are aromatic pentafluorophenol and various aliphatics: CF3CH2OH, CF2HCF2CH2OH ClCF2CF2CH2OH,C6F13C2H4OH, HOCH2CF2CFClCF2CH2OH and HOC6H4C(CF3)2C6H4OH. All these new compounds have been characterized by 1H and 13C NMR. We conclude that CTP is the best method to obtain allylic and diallylic compounds.  相似文献   

17.
Many iron‐containing enzymes involve metal–oxygen oxidants to carry out O2‐dependent transformation reactions. However, the selective oxidation of C H and CC bonds by biomimetic complexes using O2 remains a major challenge in bioinspired catalysis. The reactivity of iron–oxygen oxidants generated from an FeII–benzilate complex of a facial N3 ligand were thus investigated. The complex reacted with O2 to form a nucleophilic oxidant, whereas an electrophilic oxidant, intercepted by external substrates, was generated in the presence of a Lewis acid. Based on the mechanistic studies, a nucleophilic FeII–hydroperoxo species is proposed to form from the benzilate complex, which undergoes heterolytic O O bond cleavage in the presence of a Lewis acid to generate an FeIV–oxo–hydroxo oxidant. The electrophilic iron–oxygen oxidant selectively oxidizes sulfides to sulfoxides, alkenes to cis‐diols, and it hydroxylates the C H bonds of alkanes, including that of cyclohexane.  相似文献   

18.
Rate coefficients have been measured at 298 ± 4 K and 1000 mbar total pressure for the reactions of OH with a series of symmetrical acetals (R O CH2 O R, R = C1 to C4) using a relative kinetic technique. The investigations have been performed in a laboratory photoreactor and also in the large outdoor EUPHORE simulation chamber facility in Valencia, Spain. The following rate coefficients (in units of 10−11 cm3 molecule−1 s−1) have been obtained: dimethoxy methane (R = CH3), 0.49 ± 0.02; diethoxy methane (R = CH3CH2), 1.84 ± 0.18; di‐n‐propoxy methane (R = CH3CH2CH2), 2.63 ± 0.49; di‐iso‐propoxy methane (R = (CH3)2CH), 3.93 ± 0.48; di‐n‐butoxy methane (R = CH3CH2CH2CH2), 3.47 ± 0.42; di‐iso‐butoxy methane (R = (CH3)2CHCH2), 3.68 ± 0.57; di‐sec‐butoxy methane (R = CH3CH2C(CH3)H), 4.68 ± 0.05. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 797–803, 1999  相似文献   

19.
OH addition reactions play a pivotal role in the atmospheric transformation of a number of phenyl and substituted phenyl‐based persistent and toxic organic pollutants. Here, we screened appropriate DFT functionals to predict reaction mechanisms and rate constants (kOH) of the OH additions by taking benzene and substituted benzenes (C6H5F, C6H5Cl, C6H5Br, C6H5CH3, C6H5OH) as model compounds. By comparing the kOH values calculated with DFT methods to experimental values, we found that the ωB97 functional is the best among the 18 functionals considered (using the basis sets 6‐31 + G(d,p) for optimizations and 6‐311++G(3df,2pd) for single point energy calculations) in the temperature range of 230‐330 K. In addition, we found that some other functionals performed well in specific conditions, e.g., BMKD3 is good for benzene, halogenated benzenes and C6H5CH3, and CAM‐B3LYP is good for the reaction of C6H5OH at room temperature. Based on the diversity of the electronic structures of the selected model compounds and the frequent occurrence of certain substituents ( CH3,  OH,  F,  Cl, and  Br) in the target compounds, the functionals recommended here can be used for future study of the reaction mechanisms and kOH values for OH addition to phenyl and substituted phenyl‐based persistent and toxic organic pollutants.  相似文献   

20.
A bimolecular rate constant,kDHO, of (29 ± 9) × 10?12 cm3 molecule?1 s?1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5‐dimethyl‐1‐hexyn‐3‐ol (DHO, HC?CC(OH)(CH3)CH2CH(CH3)2) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH3)2C?O), 3‐butyne‐2‐one (3B2O, HC?CC(?O)(CH3)), 2‐methyl‐propanal (2MP, H(O?)CCH(CH3)2), 4‐methyl‐2‐pentanone (MIBK, CH3C(?O)CH2CH(CH3)2), ethanedial (GLY, HC(?O)C(?O)H), 2‐oxopropanal (MGLY, CH3C(?O)C(?O)H), and 2,3‐butanedione (23BD, CH3C(?O)C(?O)CH3). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O‐(2,3,4,5,6‐pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O‐bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas‐phase reaction mechanisms. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 534–544, 2004  相似文献   

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