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1.
A series of RuII polypyridyl complexes of the structural design [RuII(R?tpy)(NN)(CH3CN)]2+ (R?tpy=2,2′:6′,2′′‐terpyridine (R=H) or 4,4′,4′′‐tri‐tert‐butyl‐2,2′:6′,2′′‐terpyridine (R=tBu); NN=2,2′‐bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO2 to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes’ reactivities. Whereas electron‐donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [RuII(tpy)(6‐mbpy)(CH3CN)]2+ (trans‐[ 3 ]2+; 6‐mbpy=6‐methyl‐2,2′‐bipyridine) and [RuII(tBu?tpy)(6‐mbpy)(CH3CN)]2+ (trans‐[ 4 ]2+), in which the methyl group of the 6‐mbpy ligand is trans to the CH3CN ligand, show electrocatalytic CO2 reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer–chemical reaction–electron transfer), and is a direct result of steric interactions that facilitate CH3CN ligand dissociation, CO2 coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.  相似文献   

2.
The valence vibrations C? H and C? D of a number of alkanes and of (CH3)3CX are studied using compounds deuterated in specific positions. For the methyl and the methylene groups an experimental model of group frequencies is proposed, which allows some general conclusions to be drawn concerning the assignation of the frequencies. The methyl group always shows a Fermi resonance between νs and 2δas in the region of 2930–2870 cm?1. In consequence the unperturbed νsCH3 frequency may be situated at ∽2915 cm?1 and the absence of a coupling with other groups can be checked. The vibrations of the methylene group adjacent to a methyl group have higher frequencies than those of CH2 groups further removed. The coupling of the methylene group with other groups is always strong and may amount to 10 cm?1. For a chain of methylene groups, the coupling is the larger the longer the chain; being relatively small for symmetrical modes (∽3 cm?1) for the antisymmetric mode. A correlation is found between protonated and deuterated groups which leads to isotope effects comparing well with recorded values.  相似文献   

3.
Ab initio SCF and SCF -CI calculations have been performed to investigate substituent effects on ground- and excited-state properties of 4-R-pyrimidines, and to compare these with substituent effects in 2- and 4-R-pyridines, with R including the π donating and σ withdrawing groups CH3, NH2, OH, F, and C2H3 and the σ and π electron-withdrawing groups CHO and CN. Substitution leads to significant changes in the internal angles of the pyrimidine ring, which are independent of the nature of the substituent. The geometry of the pyrimidine ring is more sensitive to substitution in the 4 position than the pyridine ring geometry is to substitution in either the 2 or the 4 position. The isodesmic reaction energies for substituent transfer from the 4 position of pyrimidine to the 2 or 4 position of pyridine indicate that all R groups except CN have a relative stabilizing effect in pyrimidine. The presence of a π donating group leads to an increase in the n→π* transition energy of 4-R-pyrimidines, while the π withdrawing group CN leads to a decrease in the transition energy relative to pyrimidine. Orbital energy differences and virtual excitation energies tend to correlate with n→π* transition energies of 4-R-pyrimidines with saturated R groups, but such correlations are masked by π conjugation, n orbital interaction, and configurational mixing when the unsaturated groups C2H3, CHO, and CN are present. The electronic effects of a π donating group are stronger when the group is bonded to pyrimidine than to pyridine, but those of a π withdrawing group are weaker when the group is bonded to pyrimidine.  相似文献   

4.
A series of (hydroxymethyl)hydroxyphenyldimethylsiloxanes of linear and branched structures were synthesized by the reaction with formaldehyde in aqueous alkaline medium of organosilicon phenols of general formula R′[Si(CH3)2O] n [Si(CH3)RO] m SiMe2R′, where R′ was 4-hydroxy-3-methoxyphenylpropyl, R was methyl or 4-hydroxy-3-methoxyphenylpropyl. The structure and composition of the siloxanes were confirmed by elemental analysis, NMR and IR spectroscopy. The homocondensation of (hydroxymethyl)hydroxyphenyldimethylsiloxanes at the hydroxymethyl groups was investigated. A possibility of reaction of (hydroxymethyl) hydroxyphenyldimethylsiloxanes with phenol-formaldehyde resin to form copolymers was demonstrated.  相似文献   

5.
The properties of various atomic groups of molecules containing a carbonyl unit (XCOY) consisting of an ester (Y=OR) or amide function (Y=NHR) in different molecular environments (X=H, Me, Et, OH, OMe, NH2, NHMe, F, Cl), as well as their influence on the properties of the alkyl chain (R=C8H17) in the molecule, were analyzed by use of the theory of atoms in molecules (AIM). To this end, the main atomic and bond properties for each atom in 18 carbonyl compounds of the aforementioned types were determined on the basis of 6-31++G**//6-31G* wave functions. The properties of the C and O atoms in the carbonyl group, and those of their bonds, are directly related to the nature and electronegativity of the X substituent and to the character of the Y group. The nature of the C Y bond and the properties of the Y group are also dependent on the proximity of the X group. Based on the precision with which integrated properties were determined, assessed by L(Ω), the properties of the methylene groups of the R chain located in α and β with respect to Y are essentially dependent on the nature of Y and, to a lesser extent, on that of X. The methylene group in γ with respect to Y exhibits a dependence on the nature of the latter that vanishes in more distinct groups; therefore, the methylene in ε can be assimilated to one in an alkane. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1444–1454, 1999  相似文献   

6.
The kinetics of the Diels-Alder additions of CH2 = CHCN, CH2 = C(CH3) CN, and cis- and trans-CH3CH = CHCN to cyclohexa-1, 3-diene have been studied in the gas phase. The stereochemistry of these reactions is discussed. In terms of a biradical mechanism, a minimum value of 4.1 ± 0.8 kcal mol?1 for the stabilizing effect of a CN group vis-à-vis a methyl group is shown to fit the experimental activation energies.  相似文献   

7.
A series of 6-X-3,8-dioxatricyclo[3.2.1.02,4]octanes (X?CO2CH3, CN, Cl and CN) are studied by NMR, after their syntheses by epoxidation of the corresponding 7-oxabicyclo[2.2.1]heptenes. The NMR parameters (J, δ) are determined, and also the anisotropy effects of methyl groups at the 1,5 bridgehead positions. The results allow an unambiguous identification of the diastereo-isomers having a gem-chlorocyano group in the 6 position.  相似文献   

8.
The RPLC retention of 1,n-halo(alkylthio)alkanes on an ODS phase with methanol/water (95%/5%) has been investigated. Replacement of a methyl group in a dialkyl sulphide R-S-R by a halogen atom X, to yield the title compounds X-(CH2)n-S-R, generally results in a retention decrease. This retention loss results either from the halogen atom proper, or from its immediate vicinity, or from a reduced retention contribution of the alkyl units. The methylene groups (n) between halogen and sulphur produce somewhat greater retention than the methylene groups in the alkyl groups R.  相似文献   

9.
《合成通讯》2013,43(8):1135-1144
ABSTRACT

The title compounds wherein R = Me or i-Pr function as efficient promoters for the formation of coumarins in good to excellent yields (80–95%) from salicylaldehydes and di-activated methylene compounds of the type R′CH2CO2Et (R′ = CO2Et, COMe, CN). Although the yields are not generally superior to those reported in the literature, our methodology is more convenient in that milder conditions and shorter reaction times are facilitated by the use of the aforementioned commercially available catalysts.  相似文献   

10.
Excess enthalpies of sixteen binary mixtures between one each of methyl methylthiomethyl sulfoxide (MMTSO) and dimethyl sulfoxide (DMSO) and one of ketone {CH3CO(CH2)nCH3, n=0 to 6 and CH3COC6H5} have been determined at 298.15 K. All the mixtures showed positive excess enthalpies over the whole range of mole fractions. Excess enthalpies of ketone+MMTSO or DMSO increased with increasing the number of methylene radicals in the methyl alkyl ketone molecules. Excess enthalpies of MMTSO+ketone are smaller than those of DMSO+ketone for the same ketone mixtures. The limiting excess partial molar enthalpies of the ketone, H 1 E,∞, in all the mixtures with MMTSO were smaller than those of DMSO. Linear relationships were obtained between limiting excess partial molar enthalpies and the number of methylene groups except 2-propanone.  相似文献   

11.
A relation between the inductive and steric effects (concepts of the classical theory of molecular structure) and electron density distribution parameters was revealed by quantum chemistry methods. The propagation of the inductive and steric influence of the (CH3)3C and CH3 groups along carbon chains in tert-butylalkanes was analyzed. The steric effect of the (CH3)3C group was shown to extend to two CH2 groups, and the inductive effect, to one CH2 group. Definitions of the standard (CH3)3CCH2 and (CH3)3C(CH2)2 groups were given. Configurations of transferable groups decreasing additive approach errors were suggested. Additive procedures for calculating the properties of molecules containing (CH3)3C were refined.  相似文献   

12.
Triphenylantimony(V) heteroleptic derivatives containing substituted oximes and morpholine dithiocarbamate of the type Ph3Sb[R(R′)C:NO]2[S2CN(CH2CH2)2O] (where R = ─C6H5, R′ = ─CH3 (I); R = ─C6H4CH3, R′ = ─CH3 (II); R = ─C6H4Cl, R′ = ─CH3 (III); R = ─C6H4Br, R′ = ─CH3 (IV); R = ─C6H4OH, R′ = ─H (V); R(R′)C = CCH2(CH2)3CH2 (VI)) were synthesized by successive substitution reactions of triphenylantimony(V) dibromide with the sodium salt of substituted oximes and morpholine dithiocarbamate in unimolar ratio. All these newly synthesized derivatives were characterized using physicochemical and elemental analyses and tentative structures have been proposed on the basis of infrared, (1H, 13C) NMR and liquid chromatography–mass spectra. Spectral data revealed that the oxime behaves in a monodentate manner whereas morpholine dithiocarbamate behaves in an anisobidentate manner and thus distorted octahedral geometry has been proposed for these derivatives. Nanometric particle size (ca 25 nm) and monoclinic crystal system have been determined using power X‐ray diffraction data of two representative derivatives. Furthermore, these newly synthesized derivatives were screened against two bacteria, Bacillus subtilis (Gram‐positive) and Escherichia coli (Gram‐negative), to evaluate their antibacterial potential. Derivative VI exhibited maximum zone of inhibition (30 mm) against E. coli. Additionally two derivatives (I and II) were tested for their antioxidant potential, with derivative II exhibiting higher antioxidant potential (233 μM g?1). Structure–activity relationships were also investigated.  相似文献   

13.
Primary and secondary alcohols are easily protected as diphenylmethyl (DPM) or bis(methoxyphenyl)methyl (BMPM) ethers in good yield using PdCl2(CH3CN)2 as catalyst in dichloroethane at 60 or 20 °C, respectively. These conditions are compatible with other functional and protecting groups such as halides, esters, acetal, benzyl, para-methoxybenzyl, benzyloxycarbonyl, and tert-butyldiphenylsilyl. Good selectivity was observed in favor of primary over secondary alcohols. Deprotection of diphenylmethyl or bis(4-methoxyphenyl)methyl ethers was efficiently achieved at room temperature using PdCl2(CH3CN)2 in dichloroethane in the presence of 10 equiv of ethanol.  相似文献   

14.
在本文中,提出了极性基团电子相关能贡献的定义,并在MP2-OPT2/6-311++G(d)水平上计算了CH3(CH2) mOH( m=0-4)体系中HO-、CH3-和-CH2-基团电子相关能贡献值。计算结果表明,在CH3(CH2) mOH( m=0-4)体系中端基HO-、CH3-基团电子相关能贡献值 Ecorr(HO-)和 Ecorr(cH3-)的数值随着 m的增加而逐渐减小。同一体系中a -CH2-基团电子相关能贡献值大于其它-CH2-基团电子相关能贡献值,在CH3(CH2) mOH( m=1-4)体系中,距离端基HO-基团越远的-CH2-基团其电子相关能贡献值越小;通过计算结果可以推断,在CH3(CH2) mOH体系中随着 m的逐渐增加,相对远离端基HO-的-CH2-基团的电子相关能贡献值表现出收敛趋向并将趋于不变,此-CH2-基团可看作一个标准的亚甲基而且其 Ecorr(-cH2-)的数值在CH3(CH2) mOH体系中具有传递性。在MP2-OPT2/6-311++G(d)水平上对CH3(CH2) mOH( m=2-4)体系的计算结果和应用Gaussian 98程序在MP2/6-311++G(d)//HF/6-311++G(d)水平上对CH3(CH2) mOH( m=2-7)体系的计算结果均表明,体系总电子相关能与( m-1)呈 中 m是体系中亚甲乙烯基的数值。  相似文献   

15.
The 1H NMR spectra of a series of cis and trans-3R,4 X-cyclohexanones (-2,2,6,6-d4) are analysed. By comparison of their 3J coupling constants with those of cyclohexane homologues we obtain information about the chair–chair equilibrium constants for R = CH3, X = CN, the chair structure of cis isomers with an equatorial t-butyl group, and a conformational heterogeneity with trans (CH3)3C and CN groups. This latter situation is analysed by means of a simplified but controlled Karplus relationship, on the basis of a mixture of two conformers; this involves a diequatorial chair and a boat form with a dihedral angle Φ34 of about ?6°.  相似文献   

16.
Novel liquid crystalline photochromic materials of the type 4-R-C6H4-N=N-C6H4-O(CH2)n-N(CH2CH2OH)2, where R is NO2, H, CN, O-n-C8H17, phenyl, 4-O2NC6H4, were prepared. Some of them are photoconductive. These materials were used for the preparation of light-sensitive polymers in which the photoactive moieties were attached to polyurethane chain. Photochromism of these compounds is based on trans-cis isomerization of azobenzene group. An example of the photochromic activity is presented on solid solution of one material (R = O-n-C8H17, n = 5) in poly(methyl methacrylate) matrix.  相似文献   

17.
Bromomethyl poly (aryl ether ether ketone) has been prepared from methyl poly (aryl ether ether ketone) (MePEEK) and has been used as the precursor to many forms of functionalized PEEK. MePEEK was brominated directly with bromine. Bromination takes place exclusively at the methyl group. The reaction conditions for bromination have been studied. The bromination level can be controlled by the amount of bromine used, up to 90% of the methyl groups can be brominated to mono-bromo and di-bromo methyl PEEK. Modification reactions have been carried out on the brominated methyl PEEK. The bromomethyl group has been converted to different functional groups, such as ? CH2OH, ? CH2OCH3, ? COOCH3, ? CH2CN, ? CH2COOH ? CH2OCOCH3, ? CH2N+H (CH2CH3)2Br?, ? CH2N (CH2CH3)2, ? CH2N+ (CH2CH3)3 Br?. Published 1994 John Wiley & Sons, Inc.  相似文献   

18.
Structure and Properties of the Methyltetrafluorophosphate Anion, [CH3PF5] Methyltetrafluorphosphorane reacts with the fluorides NaF, KF, CsF, and (CH3)4NF with formation of the corresponding methylpentafluorophosphates. In case of the K and Cs salts K[CH3PF5] · CH3CN and Cs[CH3PF5] · CH3CN, respectively, are formed using acetonitrile as solvent. The salts are characterized by NMR, IR and Raman spectroscopy. The vibrational frequencies are compared with ab initio calculated data (RHF/6‐31+G*). The RHF/6‐31+G* calculation yields for the almost octahedral anion bond distances of d(PFeq) = 163.7 pm, d(PFax) = 162.0 pm, and d(PC) = 184.8 pm.  相似文献   

19.
From the temperature dependence of integrated intensities and from line widths in high-resolution 1H-NMR spectra, the relaxation times T1 and T2 of protons in CH2 and CH3 groups of polyisobutylene in CCl4 solution have been determined. Although the relaxation time T1 of methylene protons is determined mainly by intragroup interactions, intergroup interactions of two methyl groups from each two consecutive monomer units were found to contribute considerably to T1 of methyl protons. The Structure and mobility of polyisobutylene (PIB) molecules in solution is discussed on the basis of the relaxation time data.  相似文献   

20.
Ni(II) complexes of a series of pentadentate polyamine ligands have been reacted with CH3CN in the gas phase using a modified quadrupole ion trap mass spectrometer. The ligands have structural features such that upon complexation, chelate ring size, sterics, and inductive effects can be evaluated in the gas phase. Rate and equilibrium constants for CH3CN addition to the metal complexes show that there is a general decrease in the gas-phase reactivity as the chelate ring size is increased. Density functional theory calculations at the B3LYP/LANL2DZ level of theory have been used to obtain minimum energy structures and Mulliken charges for the complexes. The decreased reactivity observed as the chelate ring size is increased correlates with a decrease in the atomic charge on the metal. A larger chelate ring size enhances ligand flexibility and improves the overlap of the ligand’s donor atoms with the metal center. Adding methyl groups adjacent to or on the nitrogen donor groups of a ligand also decreases the rate and equilibrium constants for the reactions of a given complex with CH3CN. Analysis of Mulliken charges for these complexes indicates that both inductive and steric effects are responsible for lower complex reactivity. These results suggest that while the gas-phase reactivity of a metal complex with CH3CN is very dependent on the functional groups directly bound to the metal, in some cases steric effects can conceal the correlation between reactivity and coordination structure.  相似文献   

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