共查询到20条相似文献,搜索用时 15 毫秒
1.
Stefan E. Boiadjiev David A. Lightner 《Monatshefte für Chemie / Chemical Monthly》2002,133(11):1469-1480
Summary. Malonic ester derivatives of ethyl and methyl 3,5-dimethyl-4-(1′-iodoneopentyl)-1H-pyrrole-2-carboxylate exhibit restricted rotation about the pyrrole C(4)–C(1′) bond due to the bulky 1′-tert-butyl and malonic ester groups and the ortho effect at C(4) of the sterically crowded 3,5-dimethylpyrrole. The malonates belong to a rare class of atropisomers with restricted
rotation about an sp3–sp2 C–C bond, and they undergo diastereomeric separation by TLC and crystallization: the diastereomers are stable in solution
at room temperature. A crystal of one of the diastereomers, suitable for X-ray crystallography, gave the relative configuration
of the chiral axis and stereogenic center at C(1′). Dynamic NMR studies of the purified diastereomers provide kinetic and
thermodynamic parameters associated with the atropisomerism: ΔG
‡ = 132–134 kJ/mol (∼32 kcal/mol) at 383 K in C2D2Cl4 solvent.
Corresponding author. E-mail: lightner@scs.unr.edu
Received July 1, 2002; accepted July 8, 2002 相似文献
2.
Diethyl 3,3′-di-tert-butyl-4,4′-dimethyl-2,2′-bipyrrole-5,5′-dicarboxylate was synthesized in four steps from ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate. The CH2 hydrogens of the ethyl ester groups of the former are diastereotopic in the 1H-NMR, consistent with axial chirality of the bipyrrole and restricted rotation about the 2,2′-bipyrrole bond, due to the
tert-butyl groups. An X-ray structure of the crystalline target compound shows the pyrrole rings are twisted out of coplanarity
by 84.5°. 相似文献
3.
Summary. Diethyl 3,3′-di-tert-butyl-4,4′-dimethyl-2,2′-bipyrrole-5,5′-dicarboxylate was synthesized in four steps from ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate. The CH2 hydrogens of the ethyl ester groups of the former are diastereotopic in the 1H-NMR, consistent with axial chirality of the bipyrrole and restricted rotation about the 2,2′-bipyrrole bond, due to the
tert-butyl groups. An X-ray structure of the crystalline target compound shows the pyrrole rings are twisted out of coplanarity
by 84.5°.
Corresponding author. E-mail: lightner@scs.unr.edu
Received September 2, 2002; accepted September 13, 2002
Published online February 20, 2003 相似文献
4.
Hossein Reza Darabi Marjan Azimzadeh Arani Mohsen Tafazzoli Mina Ghiasi 《Monatshefte für Chemie / Chemical Monthly》2008,139(10):1185-1189
The existence of a short C–H ⋯ π (alkyl–alkyne) interaction in the structure of a strained and relatively rigid tolanophane
is expected to hinder the rotation about the C–C sp3 single bond. Variable-temperature NMR experiments (performed in three solvents, CDCl3, THF-d8, and acetone-d6) and ab initio density functional calculations were carried out to investigate its dynamic nature. An energy barrier of 48.6 kJ/mol is determined
at coalescence (210 K) with acetone-d6 which is in good agreement with calculation result (54 kJ/mol).
Correspondence: Hossein Reza Darabi, Chemistry and Chemical Engineering Research Center of Iran, Pajoohesh Blvd., km 17, Karaj
Hwy, 14968-13151 Tehran, Iran. 相似文献
5.
E. L. Cavalieri E. C. Vauthier A. Cossé-Barbi S. Fliszár 《Theoretical chemistry accounts》2000,104(3-4):235-239
Self-consistent-field computations shed light on two relevant conformations of deoxyadenosine (dA) and deoxyguanosine (dG):
one with a pseudoequatorial C1′N9 glycosyl bond and the other, a slightly more stable one, with its C1′N9 bond in a bisectional orientation. In dA, both the N3 and N7 nitrogens are plausible sites for electrophilic attack, but only N7 is a plausible site in dG. The addition of H+, CH3
+, C2H5
+ or tert-C4H9
+ onto N7 does not provoke notable structural modifications and leaves the base of dA and dG in an antiperiplanar (or nearly antiperiplanar)
position with respect to the sugar C1′O4′ bond, but N3 additions cause the base to adopt a synperiplanar or strongly chiral position. This produces strong interactions between
the purine and deoxyribose moieties, whose relief could aid the eventual cleavage of the glycosyl bond of dA. Addition of
a radical cation onto N7 reduces the dissociation energy of the glycosyl bond by an estimated 8 kcal mol−1 in dA and 4 kcal mol−1 in dG – a bond weakening likely to concur to a depurination of DNA induced by radical cations.
Received: 13 September 1999 / Accepted: 3 February 2000 / Published online: 21 June 2000 相似文献
6.
Issa Yavari Mehdi Adib Hamid R. Bijanzadeh Majid M. M. Sadegi Hossein Logmani-Khouzani Javad Safari 《Monatshefte für Chemie / Chemical Monthly》2002,11(4):1109-1113
A dynamic NMR effect is observed in the 13C NMR spectra of anhydrous quinophthalone (quinoline yellow) and its monohydrate in the vicinity of 47°C and 0°C, respectively, and is attributed to a restricted rotation around the polarized carbon–carbon double bond. The free energy of activation for this process in anhydrous quinophthalone and the monohydrate is 65±2 and 55±2 kJ · mol−1, respectively, in CDCl3. 相似文献
7.
Issa Yavari Mehdi Adib Hamid R. Bijanzadeh Majid M. M. Sadegi Hossein Logmani-Khouzani Javad Safari 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1109-1113
Summary. A dynamic NMR effect is observed in the 13C NMR spectra of anhydrous quinophthalone (quinoline yellow) and its monohydrate in the vicinity of 47°C and 0°C, respectively,
and is attributed to a restricted rotation around the polarized carbon–carbon double bond. The free energy of activation for
this process in anhydrous quinophthalone and the monohydrate is 65±2 and 55±2 kJ · mol−1, respectively, in CDCl3.
Received September 25, 2001. Accepted (revised) November 14, 2001 相似文献
8.
Lutz Preu Wolfgang Kliegel Steven J. Rettig James Trotter 《Monatshefte für Chemie / Chemical Monthly》2001,132(10):1213-1224
Summary. The structure of the dehydrogenation product 1′,3a′-dihydro-3′-((1,3-dioxoindan-2-ylidene)-phenyl-methyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′-(5′H, 6a′H)-tetrone derived from the cycloadducts (±)-(3a′S,6a′R)-1′,3a′-dihydro-3′-((R)-α-(1,3-dioxoindanyl)-benzyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′(5H,6a′H)-tetrone and/or (±)-(3a′S,6a′R)-1′,3a′-dihydro-3′-((S)-α-(1,3-dioxoindanyl)-benzyl)-5′-phenyl-spiro-(indan-2,1′-pyrrolo[3,4-c]pyrrole)-1,3,4′,6′(5H,6a′H)-tetrone, which were synthesized by 1,3-dipolar cycloaddition of N-phenylmaleimide to 2-((2-(1,3-dioxoindan-2-yl)-2-phenyl-ethenyl)-imino)-indan-1,3-dione,
was determined by X-ray analysis. Crystal data (CCD, 180 K): rhombohedral, R&3macr;;, a = 34.0871(7), c = 13.9358(5) ?, Z = 18; the structure was solved by direct methods and refined by full-matrix least-squares procedures to R(F, I ≥ 3σ(I)) = 0.053. The molecule contains a central folded ring system of two cis-fused 5-membered heterocyclic rings; each ring is nearly planar, and the angle between the rings amounts to 59.0°. Dynamic
1H NMR spectroscopy of the product revealed an exchange process caused by restricted rotation of the double bonded 1,3-indandione
moiety and the phenyl group about the Csp2-Csp2 single-bonds. Molecular modeling and complete lineshape analysis indicated a four site exchange process for which free energies
of activation and free energies could be established. ΔG
‡ values for the barriers of rotation are in the range of 57–59 kJ · mol − 1 at 273 K, which is unusually high for an unsubstituted phenyl group.
Received May 3, 2001. Accepted (revised) June 8, 2001 相似文献
9.
Issa Yavari Mehdi Adib Fatemeh Jahani-Moghaddam 《Monatshefte für Chemie / Chemical Monthly》2002,133(11):1431-1436
Summary. Protonation of the reactive 1:1-intermediate produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates
with diethyl N,N′-(naphthalene-1,8-diyl)-dioxamate leads to a vinylphosphonium salt which undergoes an intramolecular Wittig reaction to produce dialkyl-4-ethoxy-1-(8-((2-ethoxy-2-oxoacetyl)-amino)-1-naphthyl)-5-oxo-4,5-dihydro-1H-pyrrole-2,3-dicarboxylates in good yields. The title compounds exist as stable rotamers as a result of restricted rotation
around the single bond linking the naphthalene moiety and the heterocyclic system. The calculated free energy of activation
for interconversion of the atropisomers amounts to about 102±2 kJ · mol−1.
Corresponding author. E-mail: isayavar@yahoo.com
Received February 5, 2002. Accepted March 19, 2002 相似文献
10.
Bikshandarkoil R. Srinivasan Christian Näther Sunder N. Dhuri Wolfgang Bensch 《Monatshefte für Chemie / Chemical Monthly》2006,137(4):397-411
Summary. Four new organic ammonium tetrathiotungstates (N–Me–enH2)[WS4] (1), (N,N′-dm-1,3-pnH2)[WS4] (2), (1,4-bnH2)[WS4] (3), and (mipaH)2[WS4] (4), (N–Me–enH2 = N-methylethylenediammonium, N,N′-dm-1,3-pnH2 = N,N′-dimethyl-1,3-propanediammonium, 1,4-bnH2 = 1,4-butanediammonium, and mipaH = monoisopropylammonium) were synthesized by the base promoted cation exchange reaction and characterized by elemental analysis,
infrared, Raman, UV-Vis and 1H NMR spectroscopy as well as single crystal X-ray crystallography. The structures of 1–4 consist of [WS4]2− tetrahedra which are linked to the organic ammonium cations via N–H⋯S hydrogen bonding. The strength and number of the S⋯H
interactions affect the W–S bond lengths as evidenced by distinct short and long W–S bonds. The IR spectra exhibit splitting
of the W–S vibrations, which can be attributed to the distortion of the [WS4]2− tetrahedron. From a comparative study of several known tetrathiotungstates it is observed that a difference of more than
0.033 ? between the longest and shortest W–S bonds in a tetrathiotungstate will result in the splitting of the asymmetric
stretching vibration of the W–S bond. 相似文献
11.
Bikshandarkoil R. Srinivasan Christian N?ther Sunder N. Dhuri Wolfgang Bensch 《Monatshefte für Chemie / Chemical Monthly》2006,121(2):397-411
Four new organic ammonium tetrathiotungstates (N–Me–enH2)[WS4] (1), (N,N′-dm-1,3-pnH2)[WS4] (2), (1,4-bnH2)[WS4] (3), and (mipaH)2[WS4] (4), (N–Me–enH2 = N-methylethylenediammonium, N,N′-dm-1,3-pnH2 = N,N′-dimethyl-1,3-propanediammonium, 1,4-bnH2 = 1,4-butanediammonium, and mipaH = monoisopropylammonium) were synthesized by the base promoted cation exchange reaction and characterized by elemental analysis,
infrared, Raman, UV-Vis and 1H NMR spectroscopy as well as single crystal X-ray crystallography. The structures of 1–4 consist of [WS4]2− tetrahedra which are linked to the organic ammonium cations via N–H⋯S hydrogen bonding. The strength and number of the S⋯H
interactions affect the W–S bond lengths as evidenced by distinct short and long W–S bonds. The IR spectra exhibit splitting
of the W–S vibrations, which can be attributed to the distortion of the [WS4]2− tetrahedron. From a comparative study of several known tetrathiotungstates it is observed that a difference of more than
0.033 ? between the longest and shortest W–S bonds in a tetrathiotungstate will result in the splitting of the asymmetric
stretching vibration of the W–S bond. 相似文献
12.
Yue Zhu Min Pu De-Cai Fang Yong-Qiang Ji Jing He David G. Evans 《Structural chemistry》2010,21(4):817-825
Abstract
The cis–trans isomerization pathways of 3,3′-azobenzene disulphonate in the S0 and T1 states are studied by DFT method at the B3LYP/6-31G(d,p) level. In the S0 state, the cis–trans isomerization concerns the complex pathway that is characterized by the inversion of one NNC angle combined with rotation around the NC bond, and the three sequential transition states are also found on the potential energy profile. Therefore, the cis–trans isomerization of 3,3′-azobenzene disulphonate can be understood in terms of a pathway involving successive rotation, inversion, and rotation processes. The energy barrier of the S0 state is 22.79 kcal mol−1. In the T1 state, the isomerization mainly concerns the rotational pathway around the NN double bond, and the two isomers are connected through only one transition state. The isomerization of the T1 state is related to a lower energy barrier, 5.02 kcal mol−1, but requires a change in spin-multiplicity. 相似文献13.
Fattori Alberto Peter Laurence M. McCall Keri L. Robertson Neil Marken Frank 《Journal of Solid State Electrochemistry》2010,14(10):1929-1936
The electrochemical and spectroelectrochemical properties of the sensitizer dye Z907 (cis-RuLL'(SCN)2 with L=4,4′-dicarboxylic acid-2,2′-bipyridine and L'=4,4′-dinonyl-2,2′-bipyridine) adsorbed on fluorine-doped tin oxide (FTO) and TiO2 surfaces have been investigated. Langmuirian binding constants for FTO and TiO2 are estimated to be 3 × 106 M−1 and 4 × 104 M−1, respectively. The Ru(III/II) redox process is monitored by voltammetry and by spectroelectrochemistry. For Z907 adsorbed
onto FTO, a slow EC-type electrochemical reaction is observed with a chemical rate constant of ca. k = 10−2 s−1 leading to Z907 dye degradation of a fraction of the FTO-adsorbed dye. The Z907 adsorption conditions affect the degradation
process. No significant degradation was observed for TiO2-adsorbed dye. Degradation of the Z907 dye affects the electron hopping conduction at the FTO–TiO2 interface. 相似文献
14.
Issa Yavari Zinatossadat Hossaini Maryam Sabbaghan 《Monatshefte für Chemie / Chemical Monthly》2007,8(4):107-110
Protonation of the highly reactive 1:1 intermediates produced in the reaction between alkyl(aryl) isocyanides and dibenzoylacetylene
by isatin, leads to vinylnitrilium cations, which undergo carbon-centered Michael-type addition with the conjugate base of the NH-acid to produce highly functionalized 1-(3-furyl)-1H-indole-2,3-diones. A dynamic NMR effect is observed in the 1H NMR spectra of these compounds as a result of restricted rotation around the single bond linking the indole moiety and the
furan system. The free-energy of activation (ΔG
#) for this process is 69–71 ± 2 kJ mol−1. 相似文献
15.
Issa Yavari Zinatossadat Hossaini Maryam Sabbaghan 《Monatshefte für Chemie / Chemical Monthly》2007,138(2):107-110
Summary. Protonation of the highly reactive 1:1 intermediates produced in the reaction between alkyl(aryl) isocyanides and dibenzoylacetylene
by isatin, leads to vinylnitrilium cations, which undergo carbon-centered Michael-type addition with the conjugate base of the NH-acid to produce highly functionalized 1-(3-furyl)-1H-indole-2,3-diones. A dynamic NMR effect is observed in the 1H NMR spectra of these compounds as a result of restricted rotation around the single bond linking the indole moiety and the
furan system. The free-energy of activation (ΔG
#) for this process is 69–71 ± 2 kJ mol−1. 相似文献
16.
Jiawei Zhang Xiaobin Huang Hao Wei Jianwei Fu Yawen Huang Xiaozhen Tang 《Journal of Solid State Electrochemistry》2012,16(1):101-107
Solid composite polymer electrolytes consisting of polyethylene oxide (PEO), LiClO4, and porous inorganic–organic hybrid poly (cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) nanotubes were prepared using the solvent casting method. Differential scanning calorimetry
and scanning electron microscopy were used to determine the characteristics of the composite polymer electrolytes. The ionic
conductivity, lithium ion transference number, and electrochemical stability window can be enhanced after the addition of
PZS nanotubes. The electrochemical impedance showed that the conductivity was improved significantly. Maximum ionic conductivity
values of 1.5 × 10−5 S cm−1 at ambient temperature and 7.8 × 10−4 S cm−1 at 80 °C were obtained with 10 wt.% content of PZS nanotubes, and the lithium ion transference number was 0.35. The good
electrochemical properties of the solid-state composite polymer electrolytes suggested that the porous inorganic–organic hybrid
polyphosphazene nanotubes had a promising use as fillers in SPEs and the PEO10–LiClO4–PZS nanotube solid composite polymer electrolyte might be used as a candidate material for lithium polymer batteries. 相似文献
17.
Ramešová S Sokolová R Degano I Bulíčková J Zabka J Gál M 《Analytical and bioanalytical chemistry》2012,402(2):975-982
The natural flavonoid compounds quercetin (3,3′,4′,5,7-pentahydroxyflavone) and luteolin (3′,4′,5,7-tetrahydroxyflavone) are
important bioactive compounds with antioxidative, anti-allergic, and anti-inflammatory properties. However, both are unstable
when exposed to atmospheric oxygen, which causes degradation and complicates their analytical determinations. The oxidative
change of these flavonoids was observed and followed by UV–visible spectrophotometry, both in aqueous and ethanolic solutions.
The distribution of the degradation products in aqueous media was monitored by LC–MS and LC–DAD analysis. The amounts of oxidative
reaction products increase with the exposure time. The oxidative degradation reduces the pharmacological efficiency of these
antioxidants and renders analytical determination inaccurate. The oxidative changes in flavonoid test solutions can explain
the inconsistent dissociation constants reported in the literature. Dissociation constants of quercetin and luteolin were
determined both by alkalimetric titration and by UV–visible spectrophotometry under deaerated conditions. The values pK
1 = 5.87 ± 0.14 and pK
2 = 8.48 ± 0.09 for quercetin, and pK
1 = 5.99 ± 0.32 and pK
2 = 8.40 ± 0.42 for luteolin were found. 相似文献
18.
Mark A. Fox Carlo Nervi Antonella Crivello Andrei S. Batsanov Judith A. K. Howard Kenneth Wade Paul J. Low 《Journal of Solid State Electrochemistry》2009,13(10):1483-1495
The influence of aryl ring substituents X (F, OMe, NMe2, NH2, OH and O−) on the physical and electronic structure of the ortho-carborane cage in a series of C,C′-diaryl-ortho-carboranes, 1-(4-XC6H4)-2-Ph-1,2-C2B10H10 has been investigated by crystallographic, spectroscopic [nuclear magnetic resonance (NMR), UV–vis], electrochemical and
computational methods. The cage C1–C2 bond lengths in this carborane series show small variations with the electron-donating
strength of the substituent X, but there is no evidence of a fully evolved quinoid form within the aryl substituents in the
ground state. In the 11B and 13C NMR spectra, the ‘antipodal’ shift at B12, and the C1 shift correlates with the Hammett σ
p value of the substituent X. The UV–visible absorption spectra of the cluster compounds show marked differences when compared
with the spectra of the analogous substituted benzenes. These spectroscopic differences are attributed to variation in contributions
from the cage orbitals to the unoccupied/virtual orbitals involved in the transitions responsible for the observed absorption
bands. Electrochemical studies (cyclic and square-wave voltammetry) carried out on the diarylcarborane series reveal that
one-electron reduction takes place at the cage in every case with the voltage required for reduction of the cage influenced
by the electron-donating strength of the substituent X, affording a series of carborane radicals with formal [2n + 3] electron
counts.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
Fatemeh Hesami Gholam Hossein Rounaghi Massoumeh Mohajeri Somayeh Tarahomi 《Journal of solution chemistry》2011,40(8):1408-1417
The complexation reactions of 4′-nitrobenzo-15-crown-5 (4′NB15C5) with Zn2+, Mn2+, Cr3+ and Sn4+ cations were studied in acetonitrile–ethanol (AN–EtOH) binary solvent mixtures at different temperatures by the electrical
conductometry method. The stability constants of the resulting 1:1 complexes were determined from computer fitting of the
conductance versus mole ratio data. The results show that the selectivity order of 4′NB15C5 for the metal cations in the AN–EtOH
(mol-%AN=76) binary solvent at 298.15 K is: Cr3+>Mn2+≈Zn2+>Sn4+, but the selectivity order changes with the composition of the mixed solvents. A nonlinear relationship was observed between
the stability constants (log 10
K
f) of these complexes and the composition of the AN–EtOH binary solvents. The corresponding thermodynamic parameters (DHco, DSco)(\Delta H_{\mathrm{c}}^{\mathrm{o}}, \Delta S_{\mathrm{c}}^{\mathrm{o}}) were obtained from the temperature dependence of the stability constants using van’t Hoff plots. The results show that the
values and also the sign of these parameters are influenced by the nature and composition of the mixed solvents. 相似文献
20.
V. A. Mjagchenkov V. Y. Proskurina Y. Y. Gromova G. V. Bulidorova 《Colloid and polymer science》2001,279(5):468-478
The sedimentation kinetics of an ochre suspension in salt (NaCl)-containing aqueous media was studied in the presence of
ionogenic (anionic, A, and cationic, C) acrylamide copolymers with high molecular weight (M > 2 × 106) using a VT–0.5 torsion balance. The ionic strength of the dispersion medium varied in the wide range from 0.001 N to 0.4 N.
The flocculation proceeded predominantly by a `bridge' mechanism, and the fraction of macromolecules inactive in the acts
of floccule formation was significantly higher for C copolymer as compared with A copolymer. A drastic fall in the flocculating
activities of A and C copolymers when passing from salt-free to salt-containing media is caused mainly by two following events:
1. The change in the conformational state of macromolecules, primarily, in their effective dimensions
2. The participation of a certain part of electrolyte in the formation and modification of an electrical double layer around
disperse phase particles
After introducing binary compositions of A and C flocculants into salt-containing media their resultant flocculating effect
depends on the introduction mode of polymeric components. A strong difference in the magnitudes of the flocculating effect
for A and C copolymers is observed in water. In the region of high ionic strengths (0.1–0.4 N) this difference becomes far
less distinct. The flocculating activities of A and C copolymers were compared when introduced as the first (λA and λC) and the second (λA
′ and λC
′) additives. It was shown that λA/λA
′>1 and λC/λC
′>1.
Such relationship between λA and λA
′, λC and λC
′ indicates that selective interactions between A and C copolymers play an essential role in the flocculation processes. The
last statement was indirectly confirmed in the present work by the data of electrochemical and viscosimetric studies. When
using C copolymer as the second additive in the region of low ionic strengths its main function undergoes reversal, and the
copolymer begins to operate not as a flocculant, but as a stabilizer of disperse phase particles (λC < 0).
Received: 14 April 2000 Accepted: 4 August 2000 相似文献