共查询到20条相似文献,搜索用时 15 毫秒
1.
Janet E. Del Bene 《Journal of computational chemistry》1981,2(3):251-260
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
2.
Bin Wang John R. Klaehn Robert H. Neilson 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4-5):821-825
Silicon-nitrogen-phosphorus compounds of the type Me 3 SiN═PR(R′)X(X= Cl, Br, OCH2CF 3 , OPh), known as N-silylphosphoranimines,are useful precursors to both cyclic and polymeric phosphazenes.Depending on the leaving group (X), thermolysis reactions afford either cyclic trimers, [N═PR(R′)] 3 (when X = Cl, Br), or linear polymers,[N═PR(R′)]n (when X = OCH 2 CF 3 or OPh). Treatment of the P-trifluoroethoxy and P-phenoxy derivatives, Me 3 SiN═PR(R′)X (X = OCH 2 CF 3 , OPh), with alcohols at lower temperature usually results in the formation of cyclic phosphazene trimers via silyl ether elimination. Recently, we have applied these synthetic methods to the preparation of some new phosphazene systems including a series of 4-aryl-functionalized trimers and polymers and a variety of non-geminal, mixed-substituent cyclic trimers. Representative examples of the synthesis, structural characterization, and reactivity of these new phosphazenes and their Si─N─P precursors are reported here. 相似文献
3.
《中国化学会会志》2018,65(5):613-627
The general species (2,2′‐bpy)MX2 (M = Pd, Pt; X = Br, I) in a crystallization process results in an isomorphous convergence in P21/c. Yet, with polyfluorinated side chains, the general [5,5′‐(HCF2CF2CH2OCH2)2‐2,2′‐bpy]MX2 species proceeds to crystallize the isomorphous structures of 5 (M = Pt; X = I) and 6 (M = Pd; X = I) in P21/c only; structure 7 (M = Pt; X = Br) crystallizes in P21/c but is not isomorphous with 5 and 6 , and structure 8 (M = Pd; X = Br) forms differently in P–1. The causes making the system nonlinear are (1) the intramolecular CF2─H…X(─M) hydrogen bonds found in 5–7 but not in 8, and (2) in response to the transition from I to Br, bifurcated [C─H…]2 F ─C hydrogen bonds that are formed in 5 and 6 and bifurcated C─ H […F─C]2 hydrogen bonds in 7 . Additionally, the intramolecular CF2─H…X(─M) hydrogen bonding from compounds 5–7 could be affirmed by the IR studies. 相似文献
4.
《Acta Crystallographica. Section C, Structural Chemistry》2017,73(9):682-687
To enable a comparison between a C—H…X hydrogen bond and a halogen bond, the structures of two fluorous‐substituted pyridinium iodide salts have been determined. 4‐[(2,2‐Difluoroethoxy)methyl]pyridinium iodide, C8H10F2NO+·I−, (1), has a –CH2OCH2CF2H substituent at the para position of the pyridinium ring and 4‐[(3‐chloro‐2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium iodide, C9H9ClF4NO+·I−, (2), has a –CH2OCH2CF2CF2Cl substituent at the para position of the pyridinium ring. In salt (1), the iodide anion is involved in one N—H…I and three C—H…I hydrogen bonds, which, together with C—H…F hydrogen bonds, link the cations and anions into a three‐dimensional network. For salt (2), the iodide anion is involved in one N—H…I hydrogen bond, two C—H…I hydrogen bonds and one C—Cl…I halogen bond; additional C—H…F and C—F…F interactions link the cations and anions into a three‐dimensional arrangement. 相似文献
5.
Ramaswamy Murugavel Natesan Thirupathi Setharampattu S. Krishnamurthy Munirathinam Nethaji 《Heteroatom Chemistry》1995,6(1):63-70
Oxidation of the cis isomer of the λ3-cyclotriphosphazane [EtNP(OCH2CF3)]3 with trimethylamine-N-oxide (TMNO) gives the cis isomer of trioxo-λ5-cyclotriphosphazane [EtNP(O)(OCH2CF3)]3; the trans isomer of [EtNP(O)(OCH2CF3)]3 is obtained by the treatment of a cis and trans mixture of [EtNP(OCH2CF3)]3 with aqueous H2O2. The two trioxocyclotriphosphazanes have been characterized by elemental analysis, IR, and NMR (1H, 13C, 19F, and 31P) spectroscopy. The solid state structures of both the isomers have been determined by single crystal X-ray diffraction. The six-membered P3N3 ring in both the isomers exhibits a twist-boat conformation; in the cis isomer, the trifluoroethoxy substituents lie on the same side of the ring, whereas, in the trans isomer, two trifluoroethoxy groups are on one side of the ring and the third on the other side of the ring. Crystal data for cis-[EtNP(O)(OCH2CF3)]3: monoclinic, P 21/ n , a = 13.593(3), b = 9.721(2), c = 17.539(3) Å, β = 99.49(2)°, V = 2286(1) Å3, Z = 4, and Final R = 0.047. Crystal data for trans-[EtNP(O)(OCH2CF3)]3: monoclinic, P 21/ n , a = 11.685(4), b = 15.115(5), c = 13.233(5) Å, - = 102.21(3)°, V = 2284(1) Å3, Z = 4, and Final R = 0.078. 相似文献
6.
John T. Vandeberg Carl E. Moore Frank P. Cassaretto 《Magnetic resonance in chemistry : MRC》1973,5(2):57-59
Proton and boron-11 magnetic resonance spectra for several potassium para-substituted tetraarylborate compounds [KB(C6H4-pX)4, where X is H, OCH3, CH3, Br, Cl, F, CF3] have been obtained. The chemical shift between the centers of the AA′ and XX′ multiplets for the ring proton multiplets, relative to a reference chemical shift of 0·39 ppm for potassium tetraphenylborate, correlated with the corresponding Hammett σ values for the para-substituent. Additionally, the boron-11 chemical shifts gave a good correlation with corresponding σ values for the substituents. Electronegativities of para-substituted phenyl rings were calculated and found to be approximately 2·70 for all compounds studied. It was shown that electronic substituent effects do not greatly influence the electron density surrounding the central boron atom in the tetraarylborate ions. 相似文献
7.
The mass spectra of twenty-eight monosubstituted trans-stilbenes in ortho, meta, para and alpha positions with ? N(CH3)2, ? NH2, ? OCH3, ? OH, ? Br, ? Cl, ? F, ? CH3, ? COOH, ? CN and ? NO2 groups as substituents have been studied. A detailed fragmentation pathway is given for stilbene. This fragmentation, characteristic for most of the substituted stilbenes, takes place either from the molecular or from the [M - Substituent] ion. In o-nitro-, o-methoxy-,α-carboxyl- and α-methylstilbene, however, rearrangement reactions prior to fragmentation influence the fragmentation pattern. 相似文献
8.
To investigate the substituent effect on x-electron delocalization of the N-benzylideneaniline (NBA), the vertical resonance energies △E^V(θ) of eleven substituted NBAs were separated into n and a parts at the B3LYP/6-311G(d) level of the Density Functional Theory (DFT). When substituted with an electron-releasing group --OH, the calculated △E^V(θ) of NBA was increased, indicative of more resonance destabilization than the mother molecule. However, when substituted with an electron-withdrawing group -NO2, the calculated △E^V(θ) values indicated less resonance destabilization. The most destabilizing effect was observed especially when the -OH group located at the ortho-position of the aromatic ring in the fragment -N=CH-Ar. For most of the substituted NBA molecules, it was the destabilized a framework that determined the destabilizing feature of the vertical resonance energy, instead of the stabilized n system. When the -NO2 substituent at the para-position of the aromatic ring of the -N=CH-Ar group, the π system had the highest stabilizing effect while the σ framework exhibited the highest destabilizing effect. While the -NO2 substituent was at the para-position of the left aromatic ring (At-), the NBA had the least vertical resonance energy value. 相似文献
9.
《Polyhedron》1986,5(11):1785-1789
Prolonged reaction of CF3COOH with Mo(CO)3(P(OCH3)3)3 in CH2Cl2 yields the dimer [Mo(CO)2(μ(O)P(OCH3)2)P(OCH3)3CF3COO]2 in low yield. The complex has been characterized by the usual spectroscopic methods and by an X-ray crystal structure determination. The molybdenum atoms are linked by two OP bridges, the six-membered dimetallacycle adopting a twisted-boat conformation. Each molybdenum is seven-coordinated and has a capped trigonal prism geometry, the capping position being occupied by an oxygen atom of the bridging OP(OCH3)2 group. A mechanism similar to the well-known Michaelis-Arbuzov rearrangement is proposed and substantiated by the concomitant apparition of CF3COOCH3 during the reaction. 相似文献
10.
The azido tetrazolo valence isomerism of twenty 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidines with different substituents at position 5 has been studied by means of 1H NMR spectroscopy. All the compounds have been found to be tetrazoles in the solid state and in (CD3)2SO solution; in CF3COOH azido and tetrazolo isomers are in equilibrium. From equilibrium constants K and thermodynamic data determined it is concluded that in this series K depends on both electronic effects and steric requirements of the 5-substituents. A linear relation between K and σ was found for 5-arylderivatives because ΔS° keeps approximately constant and the substituent mainly operates on ΔH°. 相似文献
11.
Elimination of trichloromethyl radical from the molecular ion is the abundant fragment in the mass spectra of most of the thirteen substituted trichloracetanilides studied. Unusual ortho effects of ? OCH3, ? NO2 and ? COOH groups are noticed only after the initial ejection of trichloromethyl radical from the molecular ion. 相似文献
12.
Reversible Morphological Evolution of Responsive Giant Vesicles to Nanospheres by the Self‐Assembly of Crystalline‐b‐Coil Polyphosphazene Block Copolymers
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Silvia Suárez‐Suárez Prof. Gabino A. Carriedo Dr. Alejandro Presa Soto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4483-4491
The preparation of long‐term‐stable giant unilamellar vesicles (GUVs, diameter ≥1000 nm) and large vesicles (diameter ≥500 nm) by self‐assembly in THF of the crystalline‐b‐coil polyphosphazene block copolymers [N=P(OCH2CF3)2]n‐b‐[N=PMePh]m ( 4 a : n=30, m=20; 4 b : n=90, m=20; 4 c : n=200, m=85), which combine crystalline [N=P(OCH2CF3)2] and amorphous [N=PMePh] blocks, both of which are flexible, is reported. SEM, TEM, and wide‐angle X‐ray scattering experiments demonstrated that the stability of these GUVs is induced by crystallization of the [N=P(OCH2CF3)2] blocks at the capsule wall of the GUVS, with the [N=PMePh] blocks at the corona. Higher degrees of crystallinity of the capsule wall are found in the bigger vesicles, which suggests that the crystallinity of the [N=P(OCH2CF3)2] block facilitates the formation of large vesicles. The GUVs are responsive to strong acids (HOTf) and, after selective protonation of the [N=PMePh] block, they undergo a morphological evolution to smaller spherical micelles in which the core and corona roles have been inverted. This morphological evolution is totally reversible by neutralization with a base (NEt3), which regenerates the original GUVs. The monitoring of this process by dynamic light scattering allowed a mechanism to to be proposed for this reversible morphological evolution in which the block copolymer 4 a and its protonated form 4 a+ are intermediates. This opens a route to the design of reversibly responsive polymeric systems in organic solvents. This is the first reversibly responsive vesicle system to operate in organic media. 相似文献
13.
《应用有机金属化学》2017,31(7)
Triorganotin(IV) complexes of the type Me3Sn[OC(R1):CH(CH3)C:NR2OH] and Ph3Sn[OC(R′):CH(CH3)C:NR″OH] (R′ = ─CH3, ─C6H5; R″ = ─(CH2)2─, ─(CH2)3─) have been synthesized by the reactions of trimethyl/phenyltin(IV) chloride with the sodium salt of corresponding Schiff base ligands in unimolar ratio in refluxing tetrahydrofuran. All these compounds have been characterized using elemental analyses and their probable structures have been proposed on the basis of infrared, 1H NMR, 13C NMR, 119Sn NMR and mass spectroscopic studies. In the trimethyltin(IV) derivatives the central tin atom is tetracoordinated, whereas in the analogous triphenyltin(IV)derivatives the central tin atom is pentacoordinated. All these ligands, metal precursors and corresponding triorganotin(IV) complexes have been screened for antimicrobial activities. A comparison of activities of the ligands and their corresponding triorganotin(IV) derivatives has been made. Attempts have also been made to relate the activity to the structure of these compounds. 相似文献
14.
《Acta Crystallographica. Section C, Structural Chemistry》2017,73(8):593-599
The salts 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium saccharinate, C9H10F4NO+·C7H4NO3S−, (1), and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinate, C9H9F5NO+·C7H4NO3S−, (2), i.e. saccharinate (or 1,1‐dioxo‐1λ6,2‐benzothiazol‐3‐olate) salts of pyridinium with –CH2OCH2CF2CF2H and –CH2OCH2CF2CF3meta substituents, respectively, were investigated crystallographically in order to compare their fluorine‐related weak interactions in the solid state. Both salts demonstrate a stable synthon formed by the pyridinium cation and the saccharinate anion, in which a seven‐membered ring reveals a double hydrogen‐bonding pattern. The twist between the pyridinium plane and the saccharinate plane in (2) is 21.26 (8)° and that in (1) is 8.03 (6)°. Both salts also show stacks of alternating cation–anion π‐interactions. The layer distances, calculated from the centroid of the saccharinate plane to the neighbouring pyridinium planes, above and below, are 3.406 (2) and 3.517 (2) Å in (1), and 3.409 (3) and 3.458 (3) Å in (2). 相似文献
15.
The synthesis, characterization, and mesomorphic properties of a new type of heterocyclic compounds 1, 2 derived from benzoxazole are reported. In order to understand the relationship between the structure and the mesomorphic behavior, compounds containing a variety of polar substituents (i.e., X=H, F, Cl, Br, CH3, CF3, OCH3, NO2, CN, OH, NMe2, COOCH3) on the terminal end were prepared. The phase behavior of these mesogenic compounds was characterized and studied by differential scanning calorimetry (DSC) and polarization optical microscopy. The formation of mesophases was strongly dependent on the electronic and/or the steric factors of the substituents. In general, a mesophase was better induced by introduction of a polar substituent. Compounds (X=H) formed a crystalline phase, however, other compounds, except for X=OH, exhibited nematic or smectic A phases. Interestingly all compounds with electron-donating substituents (X=CH3, OCH3, NMe2) exhibited nematic phases, however, other compounds with electron-withdrawing substituents (X=F, Cl, Br, CF3, NO2, CN, COOCH3) formed smectic A phases. Compounds (X=NO2, CN, COOCH3) have higher clearing temperatures than those of other homologues, and the higher Tcl was attributed to an enhanced conjugative interaction. However, no linear correlation between the clearing temperature or the temperature range of mesophases with Hammett σp constants was found. The fluorescent properties of the compounds were examined. All λmax peaks of the absorption and photoluminescence spectra of compounds occurred at ca. 348-381 and 389-478 nm, respectively. Whereas, the quantum yields of some compounds were relatively low. 相似文献
16.
Andrew M. Romine Dr. Noel Nebra Andrey I. Konovalov Dr. Eddy Martin Dr. Jordi Benet‐Buchholz Prof. Vladimir V. Grushin 《Angewandte Chemie (International ed. in English)》2015,54(9):2745-2749
CuCl or pre‐generated CuCF3 reacts with CF3SiMe3/KF in DMF in air to give [Cu(CF3)4]? quantitatively. [PPN]+, [Me4N]+, [Bu4N]+, [PhCH2NEt3]+, and [Ph4P]+ salts of [Cu(CF3)4]? were prepared and isolated spectroscopically and analytically pure in 82–99 % yield. X‐ray structures of the [PPN]+, [Me4N]+, [Bu4N]+, and [Ph4P]+ salts were determined. A new synthetic strategy with [Cu(CF3)4]? was demonstrated, involving the removal of one CF3? from the Cu atom in the presence of an incoming ligand. A novel CuIII complex [(bpy)Cu(CF3)3] was thus prepared and fully characterized, including by single‐crystal X‐ray diffraction. The bpy complex is highly fluxional in solution, the barrier to degenerate isomerization being only 2.3 kcal mol?1. An NPA study reveals a huge difference in the charge on the Cu atom in [Cu(CR3)4]? for R=F (+0.19) and R=H (+0.46), suggesting a higher electron density on Cu in the fluorinated complex. 相似文献
17.
Helmut Fischer 《Journal of organometallic chemistry》1980,197(3):303-313
Pentacarbonyl(arylphenylcarbene)tungsten complexes, (CO)5W[C(p-C6H4R)C6H5] (Ia, R = OCH3; Ib, R = CH3; Ic, R = H; Id, R = Br; Ie, R = CF3) react with dimethylcyanamide (II) via insertion of the CN group into the metalcarbene bond. The formation of pentacarbonyl[dimethylamino(imino)carbene]tungsten(0) (IIIa–IIIe) follows a second-order rate law: d[III]/dt = k[I][II]. Replacement of R = H by electron-withdrawing substituents (Br, CF3) results in an increase, by electron-donating groups (CH3, OCH3) in a decrease of the reaction rate. The rate constants correlate well with Hammett's σ-constants. The activation enthalpies ΔH≠ are low (37.3–41.6 kJ mol?1), the activation entropies ΔS≠ strongly negative (?119 to ?133 J mol?1 K?1). The results are discussed on the basis of an associative stepwise mechanism with a nucleophilic attack of the CN group of II at the carbene carbon in the first reaction step. 相似文献
18.
I. S. Kislina N. B. Librovich S. G. Sysoeva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(7):1111-1116
The influence of CF3COONa on the acidity function (H 0) and IR spectra of the CF3COOH-N,N-dimethylformamide (DMF)-CF3COONa system ([CF3COOH] ≤ [DMF], [CF3COONa] = 0–3 M) and H 0 of solutions of the salt in 100% CF3COOH ([CF3COONa] = 0–1.2 M) was studied. The addition of the salt to 100% CF3COOH insignificantly changed solution acidity; H 0 passed a minimum at [CF3COONa] = 0.7 M because of the formation of (CF3COO…H…OOCCF3)? anions and destruction of acid associates in the presence of the salt. Changes in the acidity of solutions of CF3COOH in DMF caused by the addition of the salt depended on the n = [CF3COOH]/[DMF] ratio. At n = 1, the salt almost did not influence H 0. At n < 1, a substantial decrease in the acidity of solutions was observed, because the salt increased the degree of proton transfer in CF3COO…H…OC(H)N(CH3)2 quasi-ion pairs solvated by DMF molecules. 相似文献
19.
Yu. N. Polivin R. A. Karakhanov V. A. Vinokurov M. A. Silin A. A. Bratkov 《Russian Chemical Bulletin》1992,41(2):324-328
We have investigated the reactions of aromatic carboxylic acids (p-XC6H4COOH, in which X=F, Cl, Br, I, NO2, CH3, H, OCH3) with methyl thiocyanate in trifluoroacetic acid. It was shown that the starting acids are converted to S-methyl benzothioates [p-XC6H4COSCH3 (40–70%)] and the nitrile of the acid [p-XC6H4CN (20–50%)]. In addition to starting acid, in the reaction mixtures products of the reaction of CF3COOH with methyl thiocyanate were identified.Institute of Oil and Gas Problems, Russian Academy of Sciences, I. M. Gubkin State Academy of Oil and Gas, 117917 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 412–416, February, 1992. 相似文献
20.
Chin-Kuen Tai Pao-Ling Yeh Chun-Chi Chang Wen-Hao Chen Rong-Hou Wu Yu-Ma Chou Bo-Cheng Wang 《Research on Chemical Intermediates》2014,40(6):2355-2362
Recently, the organic synthesis and electronic device applications of π-conjugated polymer-based materials with low energy band gap (below 2 eV) and high values of incident photon to current efficiency have been presented. In the present study, the physical properties of polythiophene (PTH) and its derivative systems (PTs) were investigated as π-conjugated low energy band gap polymers. Density functional theory with periodic boundary condition (PBC), the B3LYP functional, and the 6-31G(d) basis set was applied to determine their geometric and electronic structures and corresponding energies (E HOMO, E LUMO, and E g = E LUMO ? E HOMO) from the monomer of thiophene and its derivatives for one-dimensional (1D) extension to polymer. The effects of 3-substitution in PTs including electron-donating (CH3–, C6H13–, OH–, Cl–, OCH3–, and CHO–) and electron-withdrawing groups (Cl–, CHO–, CN–, NO2–, CF3–, and COOH–) compared with PTH were investigated. According to the calculation results, PTs with electron-donating and electron-withdrawing substituents should exhibit red- and blue-shifts, respectively, compared with PTH. These calculation results show good agreement with experimental data and provide further information for molecular design considerations. 相似文献