Functionalised oligoenes with unusual topologies: synthesis, electrochemistry and structural studies on redox-active

New [3]- and [4]-dendralenes bearing electron-donor 1,3-dithiole and ferrocene substituents have been synthesised. Compounds 8, 15 and 17 have been characterised by single-crystal X-ray diffraction. Two of the dithiole rings of 8 are conjugated (dihedral angle 9 degrees), while the third dithiole ring is almost orthogonal to this plane, and hence its pi-electron system is isolated. For the dendralene precursor molecule 15, the substituted cyclopentadienyl ring, two C=C bonds and fused dithiole and dithiine rings comprise an extended pi-conjugated system. In molecule 17 the potential conjugation path C(6)C(3) C(4)C(5)-C5Hs is distorted by an 8 degrees twist around the C(3)-C(4) bond and a 7 degrees twist around the C(5)-C(21) bond, and the delocalisation along the chain is insignificant. Solution electrochemical data demonstrate that the dendralenes are strong pi-electron donors, which give rise to dication, radical trication or tetracation species. Spectroelectrochemical studies on compounds 7 and 10 suggest that the radical species are situated within the linear 1,2-ethylenediylidene moieties and that a conformational change may occur at the dication redox stage. UV/Vis spectroscopic data are consistent with poor cross-conjugation in these systems.     

Theoretical study and X-ray determination of bianthronyl [corrected] : long C-C bond length and preferred gauche conformation

Five X-ray crystallographic structures of bianthronyl (1, 2b-5b) revealed the presence of long central C(sp3)-C(sp3) bonds (> or =1.60 A) and mostly gauche conformation. DFT calculations were carried out to study the structural features of bianthronyl and related model molecules [corrected]. Our B3LYP/6-31G gas-phase calculation results suggest that steric effect plays a role in causing the long C-C sigma bond length (>1.60 A), nonplanarity of the anthracenone moiety (>20 degrees ), and preferred gauche conformation. However, when the gauche preference is weak, environmental effects such as solvation and packing forces can reverse it. As the degree of nonplanarity of the anthracenone moiety is consistently larger in the anti conformation than in the gauche and the ease of achieving nonplanarity is determined by flexibility of the central six-membered rings directly connected to the C(sp3)-C(sp3) bond, one way to control the structure and anti-gauche energy difference of closely related compounds is by changing the clamping group (Z) in the central six-membered ring.     

Investigation of intramolecular sulfur-nitro interactions in 2-(2′-pyridylthio)-3-nitropyridine by 13C-NMR spectroscopy and x-ray crystallography

The single crystal X-ray diffraction structure of 2-(2′-pyridylthio)-3-nitropyridine is reported. A non-bonded interaction was observed between the sulfur atom and one of the oxygen atoms of the nitro group with an interatomic distance of 2.678 A. Examination of the molecule's behavior in solution by ¹³C-nmr spin-lattice (T₁) relaxation measurements showed the non-nitro bearing pyridyl ring to reorient anisotropically about the C2′-C5′ bond axis. In contrast, the nitro substituted pyridine ring did not appear to exhibit anisotropic reorientation about the corresponding C2-C5 bond axis. Rather, approximately equivalent relaxation times were noted for all protonated ring carbons, indicating that the relaxations of this portion of the molecule were governed by the overall isotropic reorientation of the system. Based on these observations, it was concluded that the intramolecular sulfur-nitro interaction also operates in the solution state and is sufficiently strong to prevent free rotation of the substituted portion of the molecule about the C2-S bond axis.     

系列新推拉型多环共轭分子二阶非线性光学性质的理论研究

在AM1和ZINDO方法基础上,按完全态求和(SOS)公式编制了计算分子二阶非线性光学系数β_ijk和β_μ的程序,研究了一系列新推拉型多环共轭分子的结构、光谱和二阶非线性光学系数β(-2ω,ω,ω)和β(0,0,0).考察了分子共轭链长、分子骨架和给电子取代基对β_μ的影响,并设计了具有最大β_μ的新型非线性光学材料分子.     

Total synthesis of epothilone a through stereospecific epoxidation of the p-methoxybenzyl ether of epothilone C

The total synthesis of epothilone A is described by the coupling four segments 4-7 a. Three of the segments, 4, 5 and 7 a, have only one chiral center; all other chiral centers were introduced by simple asymmetric catalytic reactions. The key steps are the ring opening of epoxide 5 with acetylide 8 for the construction of the C12-C13 cis double bond and a practical hydrolytic kinetic resolution (HKR) developed by Jacobsen group for the introduction the chiral center at C3. Especially, the stereospecific epoxidation of 3-O-PMB epothilone C 3 b through long-range effect of 3-O-PMB protecting group gave high yields of the C12-C13 alpha-epoxide for the synthesis of target molecule.     

Aluminepin: aluminum analogues of borepin and gallepin

We report synthesis of dibenzoaluminepin as the first aluminepin, an aluminum analogue of borepin and gallepin. This compound contains one molecule of ethereal solvent on the Al atom, which adopts a tetrahedral geometry. The central 7-membered aluminepin ring has a boatlike conformation and was characterized by single-crystal X-ray diffraction, (1)H/(13)C NMR, and DFT studies. In addition, NICS, NBO, and theoretical calculations provide insight into the nature of the bonding and aromaticity of aluminepins.     

硝基取代亚酞菁衍生物的电子光谱和非线性光学性质的理论研究

在AM₁方法优化的几何结构基础上,用INDO/CI-SOS方法深入探讨亚酞菁(C₂₄H₁₂B₁Cl₁N₆)的硝基取代对体系的电子光谱和二阶非线性光学性质的影响.结果表明,吸电子取代基和取代基的共轭链的增长对亚酞菁的分子结构和电子光谱的最大吸收峰影响很小,但对非线性光学性质都有较大影响,随着共轭链的增长,二阶非线性光学系数大幅度增强.未被取代的亚酞菁的β₀计算值与实验值十分相符,分别为-0.73×10^-28和-0.70×10^-28esu,共轭链最长的硝基取代化合物β₀值增大到-1.47×10^-28esu,增加约近1倍.     

Total synthesis of apoptolidin: construction of enantiomerically pure fragments

A general strategy for the total synthesis of the antitumor agent apoptolidin (1) is proposed, and the chemical synthesis of the defined key building blocks (4, 5, 6, 8, and 9) in their enantiomerically pure forms is described. The projected total synthesis calls for a dithiane coupling reaction to construct the C(20)-C(21) bond, a Stille coupling reaction to form the C(11)-C(12) bond, and a Yamaguchi macrolactonization to assemble the macrolide ring, as well as two glycosidation reactions to fuse the carbohydrate units onto the molecule. First and second generation syntheses to the required fragments for apoptolidin (1) are described.     

The crystal and molecular structure of delta-9-tetrahydrocannabinolic acid b.

The crystal and molecular structure of the title compound C-22H-30O-4, has been determined by X-ray methods using 1106 reflections above background level collected by counter methods. The crystals are orthorhombic, space group P2-12-12-1 with cell dimensions a equals 16.514(2) A; b equals 14.324(2) A; c equals 8.744(1) A; there are four molecules per unit cell. The structure was refined to an R of 0.084 (weighted R-w equals 0.068). The cyclohexene and the pyran part of the molecule occurs in the half-chair conformation. The bond distances and angles, and a slight twist of the benzene ring, indicate considerable stains in the aromatic system. Both the phenolic and carboxylic group are significantly out of the plane through the aromatig ring. The angle between this plane and a plane through the cyclohexene ring is 37.7 degrees. The pentyl sidechain occurs in an extended gauche conformation, and the thermal parameters of this part of the molecule are very high. The molecules are held together by van der Waals forces in the c-directions, and hydrogen bonds (2.688 A) from phenolic to carboxylic groups in the a-b plane. There is a short ultra-molecular hydrogen bond (2.490 A) from the carboxylic group to the pyran oxygen.     

On a definition of bond energies based on localized molecular orbitals

A theoretical model is presented for defining bond energies based on localized molecular Orbitals. These bond energies are obtained by rearranging the total SCF energy including the nuclear repulsion term to a sum over orbital and orbital interaction terms and then to total orbital terms, which can be interpreted as the energies of localized orbitals in a molecule. A scaling procedure is used to obtain a direct connection with experimental bond dissociation energies. Two scale parameters are employed, the C-C and the C-H bond dissociation energy in C₂H₆ for A-B and C-H type bonds, respectively. The implications of this scaling procedure are discussed. Numerical applications to a number of organic molecules containing no conjugated bonds gives in general a very satisfactory agreement between experimental and theoretical bond energies.     

Synthesis, characterization and photovoltaic properties of thiophene copolymers containing conjugated side-chain

Five side-chain conjugated polythiophene derivatives, P1-P5, were synthesized by Stille coupling reaction. The effects of side-chain structures, bearing CC double bond, CC triple bond as well as different number of methoxy substituents on the benzene ring of the side-chains, on the optical, electrochemical, and photovoltaic properties of the polymers were investigated. From P1 to P3, the effect of CC triple bond and CC double bond was compared. The results indicate that the content of the thiophene units with the CC triple bond in their conjugated side-chains not only influences the absorption shape and intensity, but also influences the energy bandgap and the photovoltaic properties of the polymers. From P3 to P5, the effect of methoxy substituents on the benzene ring of the conjugated side-chains was compared. On increasing the number of the methoxy groups on the benzene ring of the conjugated side chains, the visible π-π^∗ absorption of the conjugated polymer backbone become stronger both in solution and in film. Electron-donating ability of the methoxy groups decreased the bandgap of the polymers. The best polymer solar cell based on P5 with a structure of ITO/PEDOT:PSS/Polymer:PCBM (1:1 wt/wt)/Mg/Al showed a power conversion efficiency of 1.45% under the illumination of AM1.5, 80 mW/cm².     

Molecular and crystalline structure of furfural diacetate nitration intermediate

X-ray crystallography established the structure of the acetyl nitrate adduct to furfural diacetate (H. Gilman and G.F. Wright (1930)) as trans-2-acetoxy-5-nitro-2,5-dihydro-2-furfural diacetate (1a). The furanoid ring is essentially planar, its geometry being similar to that of 2,5-dihydrofuran molecule, except for the interatomic distance C(3)-C(4) which is shorter than the corresponding length of double C-C bond in alkenes. The C(5)-N 1.52 Å bond significantly exceeds the standard C-N bond lengths in nitroalkanes and nitrobenzene.     

Crystal Structure of 4, 5-trans-2-Amino-1, 3, 3-tricyano-4, 5-di (4-chlorophenyl)cyclopentene. Ethanol. Monohydrate

1mTRODUCT10NSincethetimeKaganhasdem0nstratedasimplepreparationofsamariumdiio-didefromsamariummetaland1,2-diiodoethanet1),SmI2hasbeenwidelyusedinsyntheticreactionst23.Thereactivityofsamariumdiiodidetowardsvariousnitrogen-containingcomP0undshasalreadybeenexamined.Thereare,toourknowledge,noliteratureexamplesforthereductionofcyanogrouptoproduceaminowiththisreagent.Inthispaper,wediscussedthecrystalstructureofthetitlecomP0undsyn-thesizedbythereactionofsamariumdii0didereagentwithp-chloroben-zyli…     

Molecular structure and benzene ring deformation of three ethynylbenzenes from gas-phase electron diffraction and quantum chemical calculations

The molecular structures of ethynylbenzene and s-triethynylbenzene have been accurately determined by gas-phase electron diffraction and ab initio/DFT MO calculations and are compared to that of p-diethynylbenzene from a previous study [Domenicano, A.; Arcadi, A.; Ramondo, F.; Campanelli, A. R.; Portalone, G.; Schultz, G.; Hargittai, I. J. Phys. Chem. 1996, 100, 14625]. Although the equilibrium structures of the three molecules have C2v, D3h, and D2h symmetry, respectively, the corresponding average structures in the gaseous phase are best described by nonplanar models of Cs, C3v, and C2v symmetry, respectively. The lowering of symmetry is due to the large-amplitude motions of the substituents out of the plane of the benzene ring. The use of nonplanar models in the electron diffraction analysis yields ring angles consistent with those from MO calculations. The molecular structure of ethynylbenzene reported from microwave spectroscopy studies is shown to be inaccurate in the ipso region of the benzene ring. The variations of the ring C-C bonds and C-C-C angles in p-diethynylbenzene and s-triethynylbenzene are well interpreted as arising from the superposition of independent effects from each substituent. In particular, experiments and calculations consistently show that the mean length of the ring C-C bonds increases by about 0.002 A per ethynyl group. MO calculations at different levels of theory indicate that though the length of the C[triple bond]C bond of the ethynyl group is unaffected by the pattern of substitution, the C(ipso)-C(ethynyl) bonds in p-diethynylbenzene are 0.001-0.002 A shorter than the corresponding bonds in ethynylbenzene and s-triethynylbenzene. This small effect is attributed to conjugation of the two substituents through the benzene ring. Comparison of experimental and MO results shows that the differences between the lengths of the C(ipso)-C(ethynyl) and C(ipso)-C(ortho) bonds in the three molecules, 0.023-0.027 A, are correctly computed at the MP2 and B3LYP levels of theory but are overestimated by a factor of 2 when calculated at the HF level.     

Synthesis and Crystal Structure of 7,7- Dimethyl-2-amino-3-cyano-4-(3,4-methylenedioxylphenyl)- 5-oxo-5,6,7,8-tetrahydro-4H-benzo-[b]-pyran

1 INTRODUCTION Inorganic solid supports as catalysts resulting in higher selectivity, milder conditions and easier work-up has been reported as useful catalysts for many reactions [1~3]. Recently, we have reported the Knoevenagel condensation and some other reactions[4~6] catalyzed by KF-Al2O3. In this paper, we discussed the crystal structure of the title compound synthesized by the reaction of 2-cyano-3-(3,4-methylenedioxylphenyl)acrylonitrile and 5,5-dimethyl-1,3-cyclohexanedione in…     

Conjugated circuits currents in hexabenzocoronene and its derivatives formed by joining proximal carbons

We report on calculated CC bond currents for a dozen derivatives of hexabenzocoroenene in which one or more proximal carbon atoms at the molecular periphery have been bridged. The approach that we use is graph‐theoretical in nature, following our outline of this method in 2003, which is based on finding all conjugated circuits in all Kekulé valence structures of these molecules. To the π‐electrons having 4n + 2 π‐electrons are assigned anticlockwise π‐electron currents and to conjugated circuits having 4n π‐electrons are assigned π‐electron currents. One may summarize the results reported in this work by stating that CC bond currents in the compounds considered decrease on going from peripheral rings to the central ring of the molecule, and also that CC bond currents decrease by insertion of bridges to proximal peripheral benzenoid rings. © 2012 Wiley Periodicals, Inc.     

Synthesis and Crystal Structure of 9-Amino-7-（2-chlorophenyl）-6H-benzo[c]thiochromene-8,8,10（7H）-tricarbonitrile DMF Solvate

The title compound 9-amino-7-(2-chlorophenyl)-6H-benzo[c]thiochromene-8,8,10(7H)-tricarbonitrile DMF solvate(C25H20ClN5OS,Mr = 473.97) was synthesized and crystallized.The crystal belongs to triclinic,space group P1 with a = 7.6393(2),b = 10.5212(3),c = 15.0573(4) ,α = 86.797(1),β = 79.445(1),γ = 75.379(1)°,Z = 2,V = 1151.16(5) 3,Dc = 1.367 g.cm-3,μ(MoKα) = 0.285 mm-1,F(000) = 492,R = 0.0389 and wR = 0.1005 for 3455 observed reflections(I > 2σ(I)).X-ray analysis reveals that the new six-numbered ring(C(1)-C(6)) forms a skew boat conformation.The molecule links a molecule of DMF via the N(1)-H(1A)...O(1) hydrogen bond,while another hydrogen bond C(23)-H(23A)...N(2) links adjacent molecules,forming dimmers along the a axis.     

The value of the π-bond order–bond length relationship in geometry prediction and chemical bonding interpretation

The π-bond order–bond length relationship is reintroduced to the literature and extended to heteronuclear bonds by presenting graphs derived solely by theoretical methods. π-bond order and overlap population results for carbon–carbon, carbon–nitrogen, and carbon–oxygen bonds obtained from ab initio STO -3G calculations using theoretically-optimized geometries are reported for a series of pteridines and for a wide range of small organic molecules. The order–length correlation graphs are used in predicting the “intrinsic” single bond lengths for sp² – sp² and sp – sp hybridized C? C, C? N, and C? O bonds, and in evaluating the relative importance of hybridization, π-electron delocalization and bond polarization effects in causing bond shortening in conjugated and hyperconjugated molecules. The calculated value of the π-bond order for a given bond in a molecule is shown to be relatively insensitive to moderate geometry changes: Hence, a use for the correlation graphs in geometry prediction is suggested. Some results for the extended 4-21G basis set are also presented.     

The aromatic character of silacyclopropenes

Minimum energy geometries for silacyclopropene, 1,1-difluoro-,1,1-dimethyl,2,3-dimethy1-, and tetramethylsilacyclopropene have been calculated using the CND0/2 approximation. The calculations predict a remarkably small ring CSiC bond angle of about 43.6°. The average ring CC bond length is predicted to be 1.380 Å, slightly shorterthan the CC bond length in aromatic rings. Substantial stabilization of the compounds arises from π interaction between the CC double bond and acceptor orbitals on silicon giving significant aromatic character to the molecules.     

Triple-decker-sandwich versus rice-ball structures for tris(benzene)dimetal derivatives of the first-row transition metals

Compounds of the type M(2)Bz(3) (Bz = benzene, C(6)H(6)) have been of interest since the related triple-decker mesitylenechromium sandwich (1,3,5-Me(3)C(6)H(3))(3)Cr(2) has been synthesized and characterized structurally by X-ray crystallography. Theoretical studies predict the lowest-energy M(2)Bz(3) structures of the early transition metals Ti, V, and Cr to be the triple-decker sandwiches trans-Bz(2)M(2)(η(6),η(6)-μ-C(6)H(6)) having quintet, triplet, and singlet spin states, respectively. In these structures, the central benzene ring functions as a hexahapto ligand to each metal atom. The singlet rice-ball cis-Bz(2)M(2)(μ-C(6)H(6)) structures with a 2.64-? Mn═Mn double bond or a 2.81-? Fe-Fe single bond are preferred for the central transition metals Mn and Fe. Singlet triple-decker-sandwich structures trans-Bz(2)M(2)(μ-C(6)H(6)) return as the lowest-energy structures for the late transition metals Co and Ni but with the central benzene ring only partially bonded to each metal atom. Thus, the lowest-energy cobalt derivative has a trans-Bz(2)Co(2)(η(3),η(3)-μ-C(6)H(6)) structure in which the central benzene ring acts as a trihapto ligand to each metal atom. Similarly, the lowest-energy nickel derivative has a trans-Bz(2)Ni(2)(η(2),η(2)-μ-C(6)H(6)) structure in which the central benzene ring acts as a dihapto ligand to each metal atom, leaving an uncomplexed C═C double bond. The metal-metal bond orders in the singlet "rice-ball" structures cis-Bz(2)M(2)(μ-C(6)H(6)) (M = Mn, Fe) and the hapticities of the central benzene rings in the singlet late-transition-metal triple-decker-sandwich structures trans-Bz(2)M(2)(μ-C(6)H(6)) (M = Co, Ni) are governed by the desirability for the metal atoms to attain the favored 18-electron configuration.