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1.
The Hartree-Fock electron density has an important property that it is identical to the exact density to first order in the perturbation theory. For the neutral atoms from He (Z = 2) to Lr (Z = 103) in their ground state, we report an accurate analytical approximation F(r) to the spherically averaged electron densityρ(r) obtained by the numerical Hartree-Fock method. The present density functionF(r) is expressed by a linear combination of reasonable number (not more than 30) of basis functionsr ni exp(- ζ i r), and has the following properties: (i)F(r) is nonnegative, (ii)F(tr) is normalized, (iii)F(r) reproduces the Hartree-Fock moments <r k > (k = −2 to +6), (iv)F(0) is equal toρ(0), (v)F′(0) satisfies the cusp condition, and (vi)F(r) has the correct exponential decay in the long-range asymptotic region.  相似文献   

2.
New chiral polysiloxanes have been prepared as stationary phases for gas chromatography, with (S)-(–)-t-leucine-t-butylamide, (S)-(–)-t-leucine-(S)-(–)-1-phenylethylamide, (S)-(–)-t-leucine-(S)-(–)-1-(α-naphthyl)ethylamide, (S)-(–)-t-leucine-(R)-( + )-1-phenylethylamide, and (S)-(–)-t-leucine-(R)-( + )-1-(α-naphthyl)ethylamide as selectors. Immobilization is achieved by radical-induced cross-linking with 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4) and dicumyl peroxide (DCUP) as cross-linking reagents and cured at 170°C. Under these conditions, racemization of (S)-(–)-t-leucine is less than 4.5% (R) for 1 h curing, while for polysiloxanes with the conventional (S)-(–)-valine selectors about 20% of R-enantiomers are formed by racemization. In the presence of 5% (w/w) V4 and 6% of DCUP with regard to the phases, 70–80% immobilization is achieved; without V4, the degree of immobilization is about 50% for both the (S)-(–)-t-leucine and (S)-(–)-valine selectors. As the size of the amide moieties of the selectors increases from t-butyl to 1-(α-naphthyl)ethyl, the degree of immobilization decreases. If the curing time is prolonged to 2 h, the extent of racemization increases. The selectivity factors achieved for amino acid enantiomers and similar pharmaceuticals are generally higher than those obtained with the corresponding non-immobilized Chirasil-Val phases.  相似文献   

3.
The cob (I)alamin- ( 1(I) ) and the heptamethyl cob(I)ynnate- ( 2(I) ) catalyzed transformation of an epoxide to the corresponding saturated hydrocarbon 3→4→5 is examined (see Schemes 1 and 3–5). Under the reaction conditions, the epoxyalkyl acetate 3 is opened by the catalysts with formation of appropriate (b?-hydroxyalkyl)-corrinoid derivatives ( 13 , 14 , 17 , 18 , see Schemes 12 and 14). Triggered by a transfer of electrons to the Co-corrin-π system, the Co, C-bond of the intermediates is broken, generating the alkenyl acetate 4 (cf. Schemes 12 and 14) following an electrofugal fragmentation (cf. Schemes 2 and 12). The double bond of 4 is also attacked by the catalysts, leading to the corresponding alkylcorrinoids ( 15 , 19 , see Schemes 12 and 14) which in turn are reduced by electrons from metallic zinc, the electron source in the system, inducing a reductive cleavage of the Co, C-bond with production of the saturated monoacetate 5 (see Schemes 2, 5 and 12). In the cascade of steps involved, the transfer of electrons to the intermediate alkylcorrinoids ( 13–15 , 17–19 , see Schemes 12 and 14) is shown to be rate-limiting. Comparing the two catalytic species 1(I) and 2(I) , it is shown that the ribonucleotide loop protects intermediate alkylcobalamins to some extent from an attack by electrons. The protective function of the ribonucleotide side-chain is shown to be present in alkylcobalamins existing in the base-on form (cf. Chap. 4 and see Scheme 14).  相似文献   

4.
The electric dipole moment p ( r ) was computed as the integral of the permanent dipole moment of the solvent molecule μ( r ) weighted by the orientational probability distribution Ω( r ; O ) over all orientations, where O is the orientation of the solvent molecule at r . The relationship between Ω( r ; O ) and the potential of the mean torque was derived; p ( r ) is proportional to the electric field E ( r ) under the following assumptions: (1) the van der Waals (vdW) interaction is independent of the orientation of the solvent molecule at r ; (2) the solvent molecule and its electrical effect are modeled as a point dipole moment; (3) the solvent molecule at r is in a region far from the solute; and (4) μE( r ) ? kBT, where kB is Boltzmann's constant and T is absolute temperature. The errors caused by calculating near‐solute Ω( r ) and p ( r ) from E ( r ) are unclear. The results show that Ω( r ) is inconsistent with the value calculated from E ( r ) for water molecules in the first and second shells of solute with charge state Q = ±1 e, and a large variation in solvent molecular polarizability γmol(r), which appeared in the first valley of 4πr2E(r) for |Q| < 1 e. Nonetheless, p (r) is consistent with the values calculated from E (r) for |Q| ≤ 1 e. The implication is that the assumptions for calculating p ( r ) can be ignored in the calculation of the solvation free energy of biomolecules, as they pertain to protein folding and protein–protein/ligand interactions. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011  相似文献   

5.
Abstract

Acid dissociation constants for two conformational isomers of dicyclohexylcyclam, cis-anti-cis, (P) and cis-syn-cis, (N) have been determined at 25, 35 and 40°C, and thermodynamic data are estimated. It was found that (N) shows very different behaviour from (P). Stability constants of (P) and (N) toward Ni(II), Cu(II) and Zn(II) have been determined by pH-titration at 25°C by using a ligand exchange reaction. It is found that the (P) complex is more stable for Ni(II) and the (N) complex is more stable for Cu(II). Contributions of the cyclohexyl group to the macrocyclic effect (ME) have been also estimated by considering basicity corrections. It is found that substitution of the cyclohexyl group in cyclam increases ME only for the Ni(II) complex of (P).  相似文献   

6.
Abstract

2-Anilino-4,6-dimethoxy-1,3,5-triazine (13), 2-anilino-4,6-diethoxy-1,3,5-triazine (14), 2-(2′-nitoanilino) 4,6-dimethoxy-1,3,5-triazine (15) undergo alkyl rearrangement in the liquid-state, while 2-(4′-nito-anilino) 4,6-dimethoxy-1,3,5-triazine (16) undergoes methyl rearrangement in the solid-state. The crystal structure and thermal behavior of these compounds are described. 13 crystallizes in monoclinic P21/c space group, a = 11.030(4), b = 6.345(4), c = 16.315(4) Å, β = 90.76(3)°. The calculated density for Z = 4 is 1.351 Mg/m3. The number of unique reflections collected is 2092, and the final R = 0.0643 [I > 2σ(I)]. 14 crystallizes in triclinic P-1 space group, a = 7.700(2), b = 9.723(3), c = 10.154(3) Å, α = 78.78(3), β = 70.32(3), γ = 73.67(3)°. The calculated density for Z = 2 is 1.266 Mg/m3. The number of unique reflections collected is 2401, and the final R = 0.0561 [I > 2σ(I)]. 15 crystallizes in monoclinic P21/m space group, a = 11.020(3), b = 6.600(2), c = 8.409(3) Å, β = 99.72(3)°. The calculated density for Z = 2 is 1.527 Mg/m3. The number of unique reflections collected is 1153, and the final R = 0.0502 [I > 2σ(I)]. 16 crystallizes in monoclinic P21/c space group, a = 7.499(3), b = 21.846(5), c = 7.895(3) Å, β = 115.42(3)°. The calculated density for Z = 4 is 1.576 Mg/m3. The number of unique reflections collected is 2036, and the final R = 0.0757 [I > 2σ(I)].  相似文献   

7.
(E)‐α,β‐Unsaturated pyrazoleamides undergo facile dienolization to furnish copper(I)‐(1Z,3Z)‐dienolates as the major in the presence of a copper(I)‐(R)‐DTBM‐SEGPHOS catalyst and Et3N, which react with aldimines to afford syn‐vinylogous products as the major diastereoisomers in high regio‐ and enantioselectivities. In some cases, the diastereoselectivity is low, possibly due to the low ratio of copper(I)‐(1Z,3Z)‐dienolates to copper(I)‐(1Z,3E)‐dienolates. (Z)‐Allylcopper(I) species is proposed as effective intermediates, which may form an equilibrium with copper(I)‐(1Z,3Z)‐dienolates. Interestingly, the present methodology is a nice complement to our previous report, in which (E)‐β,γ‐unsaturated pyrazoleamides were employed as the prenucleophiles in the copper(I)‐catalyzed asymmetric vinylogous Mannich‐Type reaction and anti‐vinylogous products were obtained. In the previous reaction, copper(I)‐ (1Z,3E)‐dienolates were generated through α‐deprotonation, which might form an equilibrium with (E)‐allylcopper(I) species. Therefore, it is realized in the presence of a copper(I) catalyst that (E)‐α,β‐unsaturated pyrazoleamides lead to syn‐products and (E)‐β,γ‐unsaturated pyrazoleamides lead to anti‐products. Finally, by use of (E)‐β,γ‐unsaturated pyrazoleamide, (E)‐α,β‐unsaturated pyrazoleamide, (R)‐DTBM‐SEGPHOS, and (S)‐DTBM‐SEGPHOS, the stereodivergent synthesis of all four stereoisomers is successfully carried out. Then by following a three‐step reaction sequence, all four stereoisomers of N‐Boc‐2‐Ph‐3‐Me‐piperidine are synthesized in good yields, which potentially serve as common structure units in pharmaceutically active compounds.  相似文献   

8.
The fragmentation of 4-styrylquinoline (I), 4-(p-nitrostyryl)-quinoline (II), 4-(p-chlorostyryl)-quinoline (III), 4-(p-hydroxystyryl)-quinoline (IV), 4-(p-methoxystyryl)-quinoline (V), 4-(p-dimethylaminostyryl)-quinoline (VI) and 4-(p-cyanostyryl)-quinoline (VII) under electron-impact in the mass spectrometer is reported. The role and the influence of substituents on the fragmentation scheme is discussed. The loss of the substituents from the molecular ion is correlated with LCAOMO quantities.  相似文献   

9.
By reaction of GeI4, [N(nBu)4]I as iodide donor, and [NMe(nBu)3][N(Tf)2] as ionic liquid, reddish‐black, plate‐like shaped crystals are obtained. X‐ray diffraction analysis of single crystals resulted in the compositions ;alpha;‐[NMe(nBu)3](GeI4)I (Pbca; a = 1495.4(3) pm; b = 1940.6(4) pm; c = 3643.2(7) pm; Z = 16) and β‐[NMe(nBu)3](GeI4)I (Pn; a = 1141.5(2) pm; b = 953.6(2) pm; c = 1208.9(2) pm; β = 100.8(1)°; Z = 2). Depending on the reaction temperature, the one or other compound is formed selectively. In addition, the reaction of GeI4 and [N(nBu)4]I, using [ImMe(nBu)][BF4] (Im = imidazole) as ionic liquid, resulted in the crystallization of [ImMe(nBu)][N(nBu)4](GeI4)3I2 (P21/c; a = 1641.2(3) pm; b = 1903.0(4) pm; c = 1867.7(4) pm; β = 92.0(1)°; Z = 4). The anionic network of all three compounds is established by molecular germanium(IV)iodide, which is bridged by iodide anions. The different connectivity of (GeI4–I) networks is attributed to the flexibility of I regarding its coordination and bond length. Here, a [3+1]‐, 4‐ and 5‐fold coordination is first observed in the pseudo‐ternary system M/Ge/I (M: cation).  相似文献   

10.
Summary Treatment ofcis-dichlorobis(dimethyl sulphoxide)platinum(II) [1] with an excess oftert-butylamine in MeOH yieldstert-butylamine-trans-dichloro(dimethyl sulphoxide)-platinum(II) [(tr-5)], rather than thecis-diaminechloro-(dimethyl sulphoxide)platinum(II) cation expected by analogy with similar reactions reported in the literature. The correspondingcis isomer [(cis-5)] is prepared from the same reactants (and similarly from K2PtCl4 andtert-butylamine) in DMSO medium, in which the initially formedtrans compound partially isomerizes to the thermodynamically favouredcis complex. The molecular structure of (cis-5) is determined by X-ray analysis. The coordination around the Pt atom is square-planar, and the DMSO ligand is S-coordinated. The lengths of the Pt-Cl bondscis andtrans to the DMSO ligand are 2.296(11) and 2.321(10) Å, respectively, and are well within expected ranges. Interatomic distances within the amine and DMSO ligands are normal.  相似文献   

11.
The following block–comb/graft copolymers of styrene (S), isoprene (I), and butadiene (B)—PS‐b‐(PB‐g‐PB), PS‐b‐(PB‐g‐PB)‐b‐PS, (PB‐g‐PB)‐b‐P2VP, (PS‐g‐PB)‐b‐(PI‐g‐PS), (PS‐g‐PB)‐b‐(PI‐g‐PS)‐b‐(PB‐g‐PI), (PS‐g‐PB)‐b‐(PI‐g‐PS)‐b‐(PB‐g‐PI)‐b‐(PI‐g‐PS)‐b‐(PS‐g‐PB), and (PS)2(PB‐g‐PB) [where PS is polystyrene, PB is polybutadiene, P2VP is poly(2‐vinylpyridine) (2VP), and PI is polyisoprene]—were synthesized with the macromonomer strategy and anionic polymerization high‐vacuum techniques. The synthetic approach involves the synthesis and block copolymerization of styrenic macromonomers in situ without isolation. The prepared samples were characterized by size exclusion chromatography with a differential refractometer detector, size exclusion chromatography with a two‐angle laser light scattering detector, and NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4040–4049, 2005  相似文献   

12.
Controlled polymerization of acyclic N‐vinylamides, that is, N‐methyl‐N‐vinylacetamide (NMVA), N‐vinylacetamide (NVA), and N‐vinylformamide (NVF), by organotellurium‐mediated radical polymerization (TERP) is reported. The corresponding poly(N‐vinylamide)s with controlled molecular weight and low dispersity (Ð<1.25) were obtained with high monomer conversion in all cases. This is the first report on the controlled polymerization of NVF. Hydrolysis of the polymers, in particular PNVF, occurred quantitatively under mild reaction conditions, giving structurally controlled poly(vinylamine)s. Block copolymers containing poly(N‐vinylamide) and poly(vinylamine) segments were also synthesized in a controlled manner.  相似文献   

13.
The induced current density ( J ( r )) provides useful information about the electronic structure of molecules under a magnetic field ( B ). However, the analysis of its topology is cumbersome because of its vectorial nature. We show that its tropicity (direction of rotation) and its strength can be compressed in the triple product B ⋅ ∇ × J ( r ) (tp J ( r )) that is a scalar field. The topology of tp J ( r ) has clear similarities to the Laplacian of the electron density. Additionally, the topology of aromatic and antiaromatic compounds is notoriously different. The vorticity of J ( r ) is helpful to define the circulation of the current density, C, that contrary to other methods, can be easily defined for individual rings in polycyclic molecules. This allows tp J ( r ) to clearly reproduce the Clar's structure of polycyclic aromatic hydrocarbons. © 2019 Wiley Periodicals, Inc.  相似文献   

14.
The synthesis of the poly(para-phenyleneethynylene)-block-poly(ethylene oxide) block copolymer (PPE-b-PEO) ( 1 ) via condensation of endfunctionalized poly(para-phenyleneethynylene) (PPE) ( 5 ) and poly(ethylene oxide) monomethyl ether (PEO) is reported. This is achieved by the initial synthesis of a PPE homopolymer with quantitative terminal functionalization, as proven by 1H NMR and field desorption mass spectrometry (FD-MS). Reaction of the latter with PEO affords the block copolymer 1 , which was characterized by 1H NMR spectroscopy, FD-MS and gel permeation chromatography (GPC). Furthermore it is shown that matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) is a suitable method to investigate PPE-b-PEO with respect to molecular weights and copolymer composition.  相似文献   

15.
The olefinic system in 3β-methoxy-4-cholesten-6 a-ol ( 2 ) is reduced using cob (I)alamin ( 1 ( I ); see Scheme 1) as catalyst, aqueous acetic acid as solvent and metallic zinc as electron source (cf. Schemes 2 and 3). Experimental evidence for an attack of 1 ( I ) on both faces of the double bond is presented. By the same catalyst (1 R)-10, 10-dimethyl-2-pinene- 10-carbonitrile ( 9 ) is first transformed to the menthene derivative 11 (see Schemes 4 and 5). The ring opening is then followed by a fast saturation of the disubstituted olefinic system in 11 , and ultimately the remaining double bond is reduced in a slow reaction. The cis-configurated saturated menthane derivative 16 is the main final product ( 16 / 17 ≈ 10:1).  相似文献   

16.
The rate of alkylation of (2-N,N-dimethylaminophenyl)diphenylphosphine with benzyl bromide in chloroform is faster than that of the corresponding reaction of (4-N,N-dimethylaminophenyl)diphenylphosphine. This result is discussed in terms of a through-space N2p–P(IV) interaction for the former. The rate of alkaline cleavage of benzyl(4-N,N-dimethylaminophenyl)diphenylphosphonium bromide, which gives toluene, is slower than the rate of alkaline cleavage of benzyl(2-N,N-dimethylaminophenyl)diphenylphosphonium bromide, which gives dimethylaniline. This result is also discussed in terms of the through-space N2p–P(IV) interaction. The 31P NMR spectra of a series of ortho-dimethylamino-substituted triarylphosphines and benzyltriarylphosphonium halides show that the phosphorus atom is more shielded than in the corresponding para-dimethylamino compounds, as anticipated on the basis of an N2p–P(IV) interaction for the former.  相似文献   

17.
Usually, ortho lithiation of Kagan's template 1 and quenching with electrophiles leads highly diastereoselectively to planar‐chiral 1,2‐disubstituted ferrocenes. Surprisingly, lithiation of 1 with lithium diisopropylamide (LDA) followed by addition of paraformaldehyde afforded regioisomer (+)‐{[S(S)][4‐(2‐hydroxyethyl)phenyl]sulfinyl}ferrocene ( 2 ), which was converted to (+)‐{[S(S)]{4‐{2‐[(methylsulfonyl)oxy]ethyl}phenyl}sulfinyl}ferrocene ( 3 ) (Scheme 1). The desired diastereoisomer (l)‐1‐(hydroxymethyl)‐2‐(p‐tolylsulfinyl)ferrocene ( 5 ) in turn could also be obtained by ortho lithiation of 1 with LDA but by quenching with DMF to yield aldehyde 4 first, which then was reduced with NaBH4 to 5 . Finally, target compound (l)‐1‐[(dimethylamino)methyl]‐2‐(p‐tolylsulfinyl)ferrocene ( 6 ) was obtained by substitution of the OH group of 5 under mild conditions or directly by ortho lithiation of 1 with lithio‐2,4,6‐triisopropylbenzene (=2,4,6‐triisopropylphenyl)lithium; LTP) followed by quenching with N,N‐dimethylmethyleneiminium chloride. At low temperatures, reaction of 1 with LDA leads, via the preferred diastereoisomeric transition state ‘exo’‐ 7 and under extrusion of a (diisopropylamine)lithium complex of type 8 , in a highly selective manner, to diastereoisomeric ortho‐lithiated chelate (l)‐ 9 (Scheme 2). The reaction of 1 to 2 is explained by a rearrangement of (l)‐ 9 to {[S(S)] [4‐(lithiomethyl)phenyl]sulfinyl}ferrocene 10 , which is acid‐catalyzed by coordinated diisopropylamine in complexes of type 8 . This rearrangement is not observed if LTP is used as base or, in case LDA is applied, if the electrophile is sufficiently reactive at low temperatures.  相似文献   

18.
Our previous studies have found that the aerial part of Hyptis rhomboides and the seed of Hyptis suaveolens contain xanthine oxidase (XO) inhibitors, inspiring us to investigate the chemical constituents of H. suaveolens stem. The EtOH extract of H. suaveolens stem was fractionated by liquid-liquid partitioning, followed by separation over Sephadex LH-20, silica gel, and reverse-phase column chromatography, centrifugal partition chromatography, and semi-preparative RP-HPLC, to give 17 bioactive isolates. Of these, dimethyl melitrate A ( 9 ) is a new natural product, 10 is likely (7″ E)-9′-methyl melitrate A, only caffeic acid ( 2 ) is the same as those isolated from the seed of the same plant, and only nepetoidins A ( 14 ) and B ( 11 ) are the same as those from H. rhomboides stem. Nepetoidin B ( 11 ) showed the best anti-XO activity. Rosmarinic acid ( 3 ) is the most abundant (>661 ppm; w/w, dried stem), while melitric acid ( 12 ) (>277 ppm), caffeic acid ( 2 ; >125 ppm), and methyl rosmarinate ( 4 ; >81 ppm) are the major ones. This outcome could serve as a good basis for chemotaxonomy of the Hyptis plants and is beneficial for developing H. suaveolens stem as anti-hyperuricemic nutraceutical.  相似文献   

19.
The acid-base interaction of octa(m-trifluoromethylphenyl)tetraazaporphin with pyridine, 2-methylpiridine, morpholine, benzylamine, piperidine, n-butylamine, diethylamine, tert-butylamine, and triethylamine in benzene was studied. It was found that intermolecular transfer of spatially screened NH-group protons from octa(m-trifluoromethylphenyl)tetraazaporphin to morpholine, benzylamine, piperidine, n-butylamine, and tert-butylamine is characterized by unusually low values of rate constants. The effect of the structure of octa(m-trifluoromethylphenyl)tetraazaporphin, octa(n-bromophenyl)tetraazaporphin, octa(n-bromophenyl)tetraazaporphin, and octa(n-nitrophenyl)tetraazaporphin, and the nature of a base on the kinetic parameters of acid-base equilibrium is shown. A structure for complexes with proton transfer of octaphenylsubstituted tetraazaporphirins is suggested. It is revealed that they are subject to decomposition over time with the formation of low molecular colorless products.  相似文献   

20.
In the presence of ammonia, methyl N-(bromoacetyl)anthranilate ( 4 ) is cyclized into 3H-1,4-benzodiaze-pine-2,5(1H,4H)-dione ( 1 ). However, when 4 is replaced with methyl N-(chloroacetyl)anthranilate ( 6 ), the only heterocyclic product formed in the reaction is 2-(chloromethyl)quinazoline-4(3H)-one ( 7 ). Under analogous conditions, 3-haloacetamidocrotonates (9, 10) do not yield any heterocyclic products and no 1,4-diazepines can be obtained.  相似文献   

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