吩噻嗪、N-甲基吩噻嗪及其自由基正离子的结构和电子光谱的理论研究

用INDO系列方法对吩噻嗪、N-甲基吩噻嗪及其自由基正离子进行了几何构型优化, 中性分子为蝶状折叠形, 自由基正离子为平面构型。以优化构型为基础,计算了上述四种分子、离子的电荷密度、自旋密度、键序和电子光谱, 对光谱进行理论指认的同时, 讨论了从中性分子到离子谱带红移的原因。所有理论计算值均与实验值一致。     

Experimental and theoretical study on the structure and reactions of 1-methoxypropane radical cations

Structure and mechanism of thermal and photochemical reactions of radical cations of methyl n-propyl ether (MPE) were studied in irradiated freonic matrices CFCl₃, CF₂ClCFCl₂, and CF₃CCl₃ at 77 K. The quantum chemical calculations of the structure of radical cations and products of their transformations were carried out with methods based on the density functional theory (DFT). Experimental and calculation results show that the MPE radical cations are characterized by substantial delocalization of spin density to the propyl group. The action of light on the MPE radical cations in a CF₃CCl₃ matrix at 77 K results in intramolecular rearrangement yielding the distonic radical cation ^.CH₂CH₂CH₂(OH⁺)CH₃. It was found that the primary MPE radical cations underwent irreversible transformation to CH₃CH₂CH₂OCH ₂ ^. radical as a result of an ion-molecule reaction that occurred in a CF₂ClCFCl₂ matrix upon heating the sample to 110–120 K or in a CFCl₃ matrix upon increasing the solute concentration.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 105–113.Original Russian Text Copyright © 2005 by Belevskii, Feldman, Tyurin.This revised version was published online in April 2005 with a corrected cover date.     

Phosphole, pyrrole, and their tetrahydro derivatives: A theoretical study of their properties

A theoretical analysis of four molecules (phosphole, phospholane, pyrrole, and pyrrolidine) in their ground and transition states has been carried out. The transition state of phosphole is highly aromatic and a partition of its energy into atomic contributions reveals that it is the phosphorus atom that is responsible for this observation.     

A theoretical study on the hyperfine coupling constant of the radical cations of aliphatic ethers

Summary The hyperfine coupling constants of the radical cations of dimethylether, oxetane (oxacyclobutane), and tetrahydrofuran (oxacyclopentane) are studied byab-initio molecular orbital theories. The extraordinarily large hyperfine coupling constants of the protons of the ethers that have been found experimentally are analyzed to conclude that an important mechanism of the hole delocalization is the spin polarization in the H-C-O-C-H bond. It is also found that for the ethereal systems conventional molecular orbital calculations give glaringly small spin densities but the SAC-CI calculation gives remarkably improved values.     

A theoretical study of electronic spectra of radical cations of some dihydroxynaphthalenes

Electronic transition energies of radical cations of 1.2-, 1.3-, 1.6-, and 1.7?dihydroxynaphthalenes are calculated using an open-shell SCF method with configuration interaction. The results are critically analyzed and a correlation diagram is given that shows the energy-shift and intensity variation in the electronic transitions when moving from one system to another, thus revealing the characteristic behavior of the transitions depending on the positions of the hydroxyl substituents. An interesting relation connecting the electronic spectroscopy with the UV photoelectron spectroscopy is suggested on the basis of which the first ionization potentials (IPS ) of the substituted aromatic systems can be inferred from the calculated energy of the A-type (HOMO → LUMO ) transitions for their radical cations. Furthermore, the predictability of the IP s is found to be considerably increased with the incorporation of “molecular size” in the regression.     

A theoretical study for the structure of propranolol and some fluorinated derivatives

This paper reports on studies of the theoretical geometrical structure of propranolol and three of its fluorinated derivatives: 1-(2,2,2-trifluoroethylamino)-3-(1-naphthyloxy)-2-propanol [trifluoroethyl-propranolol], 1-(2,2,3,3.3-pentafluoropropylamino)-3-(1-naphthyloxy)-2-propanol [pentafluoropropyl-propranolol], and 1-(2,2,3,3,4,4,4-heptafluorobutylamino)-3-(1-naphthyloxy)-2-propanol [heptafluorobutyl-propranolol]. The semiempirical method AM1 was used to optimize the structures. In the minimum energy state the geometries of the naphthyl moiety and the non-fluorinated portions of the analogs are quite similar to that of the parent. Dipole moments, charge density distributions, and electrostatic potential distributions all point to the significance of the ether oxygen in all four compounds and the increasing contribution of the side-chain terminal to the activity of the molecule with increasing number of fluorines.     

Aryl sulfoxide radical cations. Generation, spectral properties, and theoretical calculations

Aromatic sulfoxide radical cations have been generated by pulse radiolysis and laser flash photolysis techniques. In water (pulse radiolysis) the radical cations showed an intense absorption band in the UV region (ca. 300 nm) and a broad less intense band in the visible region (from 500 to 1000 nm) whose position depends on the nature of the ring substituent. At very low pulse energy, the radical cations decayed by first-order kinetics, the decay rate increasing as the pH increases. It is suggested that the decay involves a nucleophilic attack of H(2)O or OH(-) (in basic solutions) to the positively charged sulfur atom to give the radical ArSO(OH)CH(3)(*). By sensitized [N-methylquinolinium tetrafluoborate (NMQ(+))] laser flash photolysis (LFP) the aromatic sulfoxide radical cations were generated in acetonitrile. In these experiments, however, only the band of the radical cation in the visible region could be observed, the UV band being covered by the UV absorption of NMQ(+). The lambda(max) values of the bands in the visible region resulted almost identical to those observed in water for the same radical cations. In the LFP experiments the sulfoxide radical cations decayed by second-order kinetics at a diffusion-controlled rate, and the decay is attributed to the back electron transfer between the radical cation and NMQ(*). DFT calculations were also carried out for a number of 4-X ring substituted (X = H, Me, Br, OMe, CN) aromatic sulfoxide radical cations (and their neutral parents). In all radical cations, the conformation with the S-O bond almost coplanar with the aromatic ring is the only one corresponding to the energy minimum. The maximum of energy corresponds to the conformation where the S-O bond is perpendicular to the aromatic ring. The rotational energy barriers are not very high, ranging from 3.9 to 6.9 kcal/mol. In all radical cations, the major fraction of charge and spin density is localized on the SOMe group. However, a substantial delocalization of charge and spin on the ring (almost 50% for the 4-methoxy derivative and around 30% for the other radical cations) is also observed. This suggests some conjugative interaction between the MeSO group and the aromatic system that may become very significant when a strong electron donating substituent like the MeO group is present. The ionization energies (IE) of the 4-X ring substituted neutral aromatic sulfoxides were also calculated, which were found to satisfactorily correlate with the experimental E(p) potentials measured by cyclic voltammetry.     

EPR study of the phenothiazine cation radical

The EPR parameters of the phenothiazine cation radical (PTAZ⁺) have been determined with the sample in the form of a power and in sulphuric solution. The study of the solution at different temperatures in the 77–333 K range does not indicate conformational changes affecting the α proton, but shows a difference in g-values between the powder and the solution spectra. This variation can be interpreted as originated by changes in the molecular geometry of the cation ring system due to interactions with the solvent molecules.     

A theoretical study of conformational properties of N-methyl azapeptide derivatives

The conformational properties of azapeptide derivatives, Ac-azaGly-NHMe (1), Ac-azaAla-NHMe (2), Ac-NMe-azaGly-NHMe (3), Ac-NMe-azaAla-NHMe (4), Ac-azaGly-NMe(2) (5), Ac-azaAla-NMe(2) (6), Ac-NMe-azaGly-NMe(2) (7), and Ac-NMe-azaAla-NMe(2) (8), were systematically examined by using ab initio MO and DFT methods. Structural perturbations in azapeptides resulting from cyclic substitution of a methyl group at three N-positions of an azaamino acid were studied on the basis of the structure of the simplest model azapeptide, 1. Potential energy surfaces were generated at the HF/6-31G level for 1-4 and at the HF/6-31G//HF/3-21G level for 5-8 by rotating two key dihedral angles (phi, psi) in increments of 30 degrees. The backbone (phi, psi) angles of the minima for 1-4 are observed at the i + 2 position to form the betaI(I')-, betaII(II')-, betaVI-turns or the polyproline II structure according to the orientation of the acetyl group and the positions of the N-methyl groups. Compounds 5-8 coupled to a secondary amine were found to preferentially adopt polyproline II, betaI(III)-turn, or alpha-helical structure or even extended conformations depending on the orientation of the acetyl group and the positions of the N-methyl groups. Furthermore, N-methyl groups, depending on their positions, were found to affect the orientation of the amide group in the lowest energy conformations, the pyramidality of the N2 atom, and the bond length in azapeptide derivatives. These unique theoretical conformations of N-methyl azapeptide derivatives could be utilized in the definite design of secondary structure for peptides and proteins, and in the development of new drugs and molecular machines.     

New reactions of phenothiazine green cations and their metal complexes

New reactions of phenothiazine green cations and their complexes with copper and iron chlorides of both ionic and radicalic type leading to C- and N-derivatives of 3,10′-diphenothiazine are described.     

Effects of salts on the stability of the cationic radical of phenothiazine derivatives

Effects of cations and anions of various salts on the stability of the diethazine cation radical were studied in various mineral acids. It was found that stability is enhanced in the presence of salts that contain the same anion as that contained in the cation radical salt. Other anions decrease the stability. The influence of salt cations is negligible.     

The o-, m-, and p-benzyne radical cations: a theoretical study

On the basis of the CASPT2 (multiconfigurational second-order perturbation theory) geometry optimization calculations, the ground states of the o-C(6)H(4)(+) (C(2v)), m-C(6)H(4)(+) (C(2v)), and p-C(6)H(4)(+) (D(2h)) radical cations were determined to be 1 (2)B(1), 1 (2)A(2), and 1 (2)B(1u), respectively. For o-C(6)H(4)(+) and m-C(6)H(4)(+), the first excited states (1 (2)A(2) and 1 (2)A(1), respectively) lie very close to the respective ground states. The small distance value of 1.419 A between the two dehydrocarbons in the ground-state geometry of m-C(6)H(4)(+) indicates that there is a real chemical bond between the two dehydrocarbons (the distance in the 1 (2)A(1) geometry of m-C(6)H(4)(+) is very long as in the m-C(6)H(4) molecule). The (U)B3LYP isotropic proton hfcc (hyperfine coupling constant) calculation results imply that the ground and first excited states of o-C(6)H(4)(+) will have similar ESR spectrum patterns while the ground and first excited states of m-C(6)H(4)(+) will have completely different ESR spectrum patterns.     

Isomerization and fragmentation reactions of gaseous phenylarsane radical cations and phenylarsanyl cations. A study by tandem mass spectrometry and theoretical calculations

The unimolecular reactions of radical cations and cations derived from phenylarsane, C6H5AsH2 (1) and dideutero phenylarsane, C6H5AsD2 (1-d2), were investigated by methods of tandem mass spectrometry and theoretical calculations. The mass spectrometric experiments reveal that the molecular ion of phenylarsane, 1*+, exhibits different reactivity at low and high internal excess energy. Only at low internal energy the observed fragmentations are as expected, that is the molecular ion 1*+ decomposes almost exclusively by loss of an H atom. The deuterated derivative 1-d2 with an AsD2 group eliminates selectively a D atom under these conditions. The resulting phenylarsenium ion [C6H5AsH]+, 2+, decomposes rather easily by loss of the As atom to give the benzene radical cation [C6H6]*+ and is therefore of low abundance in the 70 eV EI mass spectrum. At high internal excess energy, the ion 1*+ decomposes very differently either by elimination of an H2 molecule, or by release of the As atom, or by loss of an AsH fragment. Final products of these reactions are either the benzoarsenium ion 4*+, or the benzonium ion [C6H7]+, or the benzene radical cation, [C6H6]*+. As key-steps, these fragmentations contain reductive eliminations from the central As atom under H-H or C-H bond formation. Labeling experiments show that H/D exchange reactions precede these fragmentations and, specifically, that complete positional exchange of the H atoms in 1*+ occurs. Computations at the UMP2/6-311+G(d)//UHF/6-311+G(d) level agree best with the experimental results and suggest: (i) 1*+ rearranges (activation enthalpy of 93 kJ mol(-1)) to a distinctly more stable (DeltaH(r)(298) = -64 kJ mol(-1)) isomer 1 sigma*+ with a structure best represented as a distonic radical cation sigma complex between AsH and benzene. (ii) The six H atoms of the benzene moiety of 1 sigma*+ become equivalent by a fast ring walk of the AsH group. (iii) A reversible isomerization 1+<==>1 sigma*+ scrambles eventually all H atoms over all positions in 1*+. The distonic radical cation 1*+ is predisposed for the elimination of an As atom or an AsH fragment. The calculations are in accordance with the experimentally preferred reactions when the As atom and the AsH fragment are generated in the quartet and triplet state, respectively. Alternatively, 1*(+) undergoes a reductive elimination of H2 from the AsH2 group via a remarkably stable complex of the phenylarsandiyl radical cation, [C6H5As]*+ and an H2 molecule.     

A study of the electronic structure and properties of the propargyl radical

By means of B3LYP/6-311++G(3df,3pd) the electron density distribution in the propargyl radical CH₂CCH is obtained. Within the Quantum Theory of Atoms in Molecules the phenomenon of conjugation and the spin density distribution of the unpaired electron in CH₂CCH are studied at the qualitative level. Characteristics of the electronic structure of CH₂CCH and its parent molecules CH₃–C≡CH and CH₂=C=CH₂ are compared. With the use of the rigid rotator-anharmonic oscillator model the thermodynamic properties of the propargyl radical and enthalpies of bond cleavage in propyne and allene are calculated in the temperature range 298-1500 K. The relationship between the electronic and thermodynamic properties of CH₂CCH is considered and its conjugation energy is calculated.     

Synthesis and properties of phenothiazine derivatives. I. Synthesis and properties of bisoxytriazenes containing the phenothiazine fragment

3, 7-Bis(1-phenyl-3-hydroxytriazenyl)phenothiazine has been synthesized from phenothiazine. This compound decomposes to phenyl radicals, nitrogen and 3, 7-bisnitrosophenothiazine under the influence of nitroso compounds and oxidizing agents (PbO₂, Ag₂O). The reaction of bishydroxytriazenylphenothiazene with 2, 4, 6-tribromonitrosobenzene has been studied by EPR spectroscopy.N. P. Ogarev Mordov State University, Saransk 430000. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1284–1287, September, 1996. Original article submitted March 21, 1996.     

A theoretical study on the vibrational spectra and thermodynamic properties for the nitro derivatives of phenols

The nitro derivatives of phenols are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G* level. Their IR spectra are obtained and assigned by vibrational analysis and are reliable compared with the experimental results. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties are evaluated, which are linearly related with the number of nitro and hydroxy groups as well as the temperature, obviously showing good group additivity.     

ESR and theoretical studies of trimer radical cations of coronene

Highly resolved ESR spectra of monomer, dimer and trimer radical cations of coronene (C24H12) were observed at room temperature for a solution of 1,1,1,3,3,3-hexafluoro-2-propan-2-ol (HFP) containing thallium(III) trifluoroacetate as oxidant. The spectra consisting of multiple lines with isotropic 1H-hyperfine splitting (hfs) constants of 0.0766 mT (24H) and 0.013 mT (6H) were attributable to a mixture of the dimer with the trimer radical cations, (C24H12)2+ and (C24H12)3+. For (C24H12)2+, the 1H-hfs constant agreed well with the reported value, 0.077 mT. However, for (C24H12)3+, the values were significantly different from the reported ones, 0.117 mT (12H) and 0.020 mT (24H), by Ohya Nishiguchi et al. [H. Ohya-Nishiguchi, H. Ide, N. Hirota, Chem. Phys. Lett. 66 (1979) 581], but rather similar to those reported by Willigen et al. [H. van Willigen, E. De Boer, J.T. Cooper, W.F. Forbes, J. Chem . Phys. 49 (1968) 1190]. In conflict with Willigen's report, however, no ESR line broadening which has been ascribed to a low stationary concentration of (C24H12)3+ was detected. Based on ab initio MO calculations for benzene as a compact model of C24H12, the structure of (C24H12)3+ was investigated in terms of the observed 1H-hfs constants. A staggered sandwich C(2v) structure was suggested being at the "global" minimum for the benzene trimer cation. In the structure, the unpaired electron spin is predominantly localized to the central ring, which is qualitatively in agreement with the previous ESR results of (C24H12)3+ by Ohya-Nishiguchi et al. In addition, as a "local" minimum, the benzene trimer was indicated to have a slipped sandwich Cs structure, which is less stable by ca. 19 kJ mol(-1) than the "global" minimum. In this structure, the unpaired electron spin was nearly equally distributed on both the central and one of the two side C24H12 molecules. The observed 1H-hfs constants were possibly attributable to the (C24H12)3+ cation with the analogous slipped sandwich Cs structure.     

The formation and structure of radical cations

ions generated from a number of different presursors have been studied by high kinetie energy ion—molecule reations. It has been shown that at least four distinct stable species oeeur, of which acetonitrile and methyl isoeyanide retain their original structure. With imidazole or pyrazole as precursors, a mixture of open thain radical cations, not identical to the above species and probably interconvertible via the 1H-azirine radocal cation, is formed. From butrynitrile, pyrrole, crotonitrile, allyl interconvertible via the and cyanocyopropane a fourth species, probably the vinylidenimine ion, is formed.     

The structure of diphosphine radical cations

When R₂NNR₂ molecules lose an electron to give (R₂NNR₂)^+· radical cations, the whole unit becomes planar, with a(π₁)²(π₂)¹ configuration. However, because R₃P molecules are far more strongly pyramidal than R₃N molecules, this flattening on electron loss is less, and phosphorous centred radical cations do not achieve planarity. This is clearly so for (R₂PPR₂)⁺ centres, whose liquid and solid state spectra analysed herein in terms of two equivalent ³¹P hyperfine couplings, show ca. 9% 3s character. This indicates considerable bending at each phosphorous centre. Furthermore, the form of the spectra, with no x — y splitting of the ‘perpendicular’ lines, suggests that each ³¹P coupling shares a common axis. This means that a trans conformation is required, as expected because this relieves steric strain and favours “π” type orbital overlap.