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
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
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
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(CHC(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
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
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
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 >CS, >CC<, CH2 CH2 , (CC)SnC4 − n, C (CS) S , S (CS) 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
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
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
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: CF3CH2OH, CF2HCF2CH2OH ClCF2CF2CH2OH,C6F13C2H4OH, HOCH2CF2CFClCF2CH2OH and HOC6H4C(CF3)2C6H4OH. 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
Many iron‐containing enzymes involve metal–oxygen oxidants to carry out O2‐dependent transformation reactions. However, the selective oxidation of C H and CC 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
•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