Theoretical study of two C30H20 isomers with a dodecahedrane cage and two pentaprismane cages sharing two pentagons

Structures, energies, and vibrational frequencies have been calculated for two C₃₀H₂₀ isomers with a dodecahedrane cage and two pentaprismane cages at the B3LYP/6‐31G* level of theory. Thus, two C₃₀H₂₀ isomers have the form of coplanar tri‐cage molecules. The symmetry of one C₃₀H₂₀ isomer is of D_5d and that of another is of C_2V. The heat of formation for two C₃₀H₂₀ isomers have been estimated. Heats of formation of two C₃₀H₂₀ isomers as well as the vibrational analysis indicate that two C₃₀H₂₀ isomers enjoy sufficient stability to allow for its experimental preparation. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Theoretical study of two C50H40 isomers with three dodecahedrane cages sharing two pentagons

Structures, energies, and vibrational frequencies have been calculated for two C₅₀H₄₀ isomers with three dodecahedrane cages sharing two pentagons at the B3LYP/6‐31G* level of theory. Thus, two C₅₀H₄₀ isomers have the form of coplanar tri‐dodecahedrane‐cage molecules. The symmetry of one isomer is D_5d and that of another is C_2V. Heats of formation and vertical ionization energies for two C₅₀H₄₀ isomers have been estimated in this study. Heats of formation as well as vibrational analysis indicate that two C₅₀H₄₀ isomers enjoy sufficient stability to allow for its experimental preparation. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Structures and stabilities of [C3H2]+ ˙ and [C3H2]2+ ions

Ab initio molecular orbital theory using basis sets up to 6-311G^{* *}, with electron correlation incorporated via configuration interaction calculations with single and double substitutions, has been used to study the structures and energies of the C₃H₂ monocation and dication. In agreement with recent experimental observations, we find evidence for stable cyclic and linear isomers of [C₃H₂]^{+ ˙}. The cyclic structure (, a) represents the global minimum on the [C₃H₂]^{+ ˙} potential energy surface. The linear isomer (, b) lies somewhat higher in energy, 53 kJ mol^?1 above a. The calculated heat of formation for [HCCCH]^{+ ˙} (1369 kJ mol^?1) is in good agreement with a recent experimental value (1377 kJ mol^?1). For the [C₃H₂]²⁺ dication, the lowest energy isomer corresponds to the linear [HCCCH]²⁺ singlet (h). Other singlet and triplet isomers are found not to be competitive in energy. The [HCCCH]²⁺ dication (h) is calculated to be thermodynamically stable with respect to deprotonation and with respect to C? C cleavage into CCH⁺ + CH⁺. The predicted stability is consistent with the frequent observation of [C₃H₂]²⁺ in mass spectrometric experiments. Comparison of our calculated ionization energies for the process [C₃H₂]^{+ ˙} → [C₃H₂]²⁺ with the Q_min values derived from charge-stripping experiments suggests that the ionization is accompanied by a significant change in structure.     

Withasteroids ofPhysalis VI.1H and13C NMR spectra of withasteroids ixocarpalactone A and ixocarpanolide

The¹H and¹³C NMR spectra of two withasteroids isolated fromPhysalis ixocarpa Brot. have been studied in detail. Their spectral characteristics are discussed. A comparison of the results obtained has led to the identification of a withasteroid with the composition C₂₈H₄₀O₈, mp 291–292°C (from methanol) as ixocarpalactone A, in spite of some difference in its physical constants. The other compound, with mp 252–253°C (from methanol), had the composition C₂₈H₄₀O₆, [] _D ²⁰ +27±4°, is new and has been called ixocarpanolide. The structure of 5,20R-dihydroxy-1-oxo-6, 7-epoxy-22R-witha-2-enolide has been proposed for it.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 326–332, May–June, 1986.     

Carbodications. I. The structures and energies of C4H isomers

At high levels of ab initio theory (6-31G*//4-31G), the most stable C₄H isomer is indicated to be the nonplanar cyclobutadiene dication ( 1a ); the planar form, 1b , is indicated to be 7.5 kcal/mol less stable. The second most stable C₄H isomer, the methylenecyclopropene dication, is indicated to prefer the perpendicular ( 2a ) over the planar ( 2b ) arrangement by 7 kcal/mol. The “anti van't Hoff” cyclo-(HB)₂C?CH₂ system ( 4 ), isoelectronic with 2 , also prefers the perpendicular conformation ( 4a ), and retains the C?C double bond. The linear butatriene dication ( 3 ) is the least stable C₄H species investigated. The perpendicular (D_2d) arrangement ( 3a ), permitting double allyl cationlike conjugation, is preferred over the planar D_2h form ( 3b ) by 26 kcal/mol. The heat of formation of the most stable form of C₄H, 1a , is estimated to be 623–640 kcal/mol. This species should be thermodynamically stable toward dissociation into smaller charged fragments.     

Orientation of endohedral H2, CO,and LiH inside heptagon‐containing C58 and C58H18

Three H₂@C₅₈H_x, six CO@C₅₈H_x, and six LiH@C₅₈H_x (x = 0 and 18) complexes were optimized using B3LYP/6‐31G* method. The results show that both C₅₈ and C₅₈H₁₈ destabilize nonpolar H₂ and weakly polar CO, and stabilize strongly polar LiH inside their cages. Three H₂@C₅₈H_x (x = 0 and 18) complexes are nearly equivalent in energy, and CO orients the longest direction of cage because of spatial repulsion between them in the most stable CO@C₅₈H_x (x = 0 and 18) isomers. Orientation of LiH inside C₅₈H_x (x = 0 and 18) cages is determined by dipole‐induced dipole attractive interaction between them, and this attraction is especially significant in LiH@C₅₈H₁₈ complexes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

A shock-tube study of the kinetics of reaction of hydroxyl radicals with H2, CO,CH4, CF3H,C2H4, and C2H6

Concentration-time profiles have been measured for hydroxyl radicals generated by the shock-tube decomposition of hydrogen peroxide in the presence of a variety of additives. At temperatures close to 1300°K the rate constants for the reaction are found to be in the ratio 0.18:0.19:0.59:1.00:2.33:2.88 for the additives CO:CF₃H:H₂:CH₄:C₂H₄:C₂H₆, respectively.     

Massenaufgelöste Übergangssignale der Ionen C3H5O+ und C4H7O+

Abundance ratios of C₂H₄ and CO loss (CH₄ and O loss) in the field-free region of a mass spectrometer have been determined by mass resolution of metastable peaks. Using the method ofShannon andMcLafferty the abundance ratios have been applied to characterize the structure of metastable ions. C₃H₅O⁺ ions from 10 compounds and C₄H₇O⁺ ions from 14 compounds have been examined. In the case of C₃H₅O⁺, three types of structurally different isomers are present. C₄H₇O⁺ ions represent a not equilibrating mixture of different. structures in some cases. From examination of 2-pentanone-1,1,1,3,3-d ₅, metastable C₄H₇O⁺ ions from 2-pentanone have been shown to consist of two structurally distinct types of ions which are assumed to be $$\begin{array}{*{20}c} {CH_2 - O^ + } \\ {\begin{array}{*{20}c} | & {||} \\ \end{array} } \\ {CH_2 - C - CH_3 } \\ \end{array}$$ and butyryl ion.     

Gaseous [C2H3O]+ ions

[C₂H₃O]⁺ ions with the initial structures [CH₃CO]⁺, and [CH₂CHO]⁺ cannot be distinguished on the basis of their collisional activation spectra, demonstrating that these isomers interconvert at energies below their threshold for decomposition. Self-protonation of ketene leads to the [CH₃CO]⁺ ion, while the [C₂H₃O]⁺ ion generated from glycerol most probably has the structure of an oxygen protonated ketene [CH₂?C?OH]⁺.     

Syntheses of(C_8H_8)Ln(C_9H_7)·(THF)_2(Ln=Pr,Nd)and crystal structure of(C_8H_8)Pr(C_9H_7)·(THF)_2

This paper reports two lanthanide complexes of formula (C_9H_7)Ln(C_8H_8)·(THF)_2 whereLn is Pr or Nd,C_9H_7 is indenyl,and C_8H_8 is cyclooctatetraene (COT).The complexes were preparedby the reaction of LnCl_3 with K(C_9H_7) and K_2(C_8H_8) in THF.(C_9H_7)Pr(C_8H_8)·(THF)_2 crystallizes inTHF at - 15℃ in the monoclinic space group P2_1:with unit cell dimensions a=8.446(0),b=10.083(2),c=13.407(3),β=105.48(1)°,V=1100.43(35)~3,Dc=1.52g/cm~3 and Z=2.The final R valueis 0.033,R_w value is 0.030,respectively.In (C_9H_7)Pr(C_8H_8)·(THF)_2 a five-membered ring centroid ofC_9H_7,the C_8H_8 ring centroid and the two oxygen atoms from the two THF molecules form a distortedtetrahedral geometry around the metal.     

Ab initio Study of the Structure of the Molecular Forms of C3H4O2

The geometrical parameters, force fields, and vibration frequencies were calculated by the ab initio SCF MO LCAO technique using extensive basis sets of Cartesian Gaussian functions for a number of structural isomers of the C₃H₄O₂ molecule. The relative energies of all the isomers were refined in terms of second-order Möller–Plesset (MP2) perturbation theory including electron correlation. For the most energetically favorable forms of the C₃H₄O₂ molecule, geometry optimization was fulfilled in the MP2 approximation. For the main conformer, -hydroxypropenal, possessing a chelate OCCCO fragment, the data are compared with the experimental and theoretical data available in the literature. The MP2 calculated internuclear distances and bond angles are in good agreement with the experimental values. For each form of the C₃H₄O₂ molecule, the geometrical and electronic structure is analyzed. It is shown that the presence of an intramolecular hydrogen bond is the characteristic feature of the structure of the isomers and an additional stabilizing factor.     

Strain in nonclassical silicon hydrides: An insight into the “ultrastability” of sila‐bi[6]prismane (Si18H12) cluster with the endohedrally trapped silicon atom,Si19H12

The recently postulated concept of “ultrastability” and “electron‐deficient aromaticity” (Vach, Nano Lett 2011, 11, 5477; Vach, J Chem Theory Comput 2012, 8, 2088) in a sila‐bi[6]prismane having an additional entrapped silicon atom, Si₁₉H₁₂, has been disproved on the basis of a careful analysis of the energetic characteristics related to the formation of this and other silicon hydrides. The central silicon atom in Si₁₉H₁₂ is weaker bound to other silicon atoms than in conventional tetrahedral silanes; moreover, Si₁₉H₁₂ possesses a significant amount of strain. The role of strain in the formation of the title compounds has been further rationalized by calculating the relative energies for the transformation to a half‐planar conformation in methane and in silane and by calculating the respective strain energies. The strain energy value in Si₁₈H₁₂ is equal to 9.93 eV whereas the same property for Si₁₉H₁₂ lies in range of 6.42–8.85 eV. Two low‐energy isomers of Si₁₉H₁₂ which lie by 2.77 and 3.42 eV (!) lower in energy than the originally considered sila‐bi[6]prismane‐based structure have been proposed. © 2015 Wiley Periodicals, Inc.     

Structures of Chlorinated Fullerenes,IPR C96Cl20 and Non‐classical C94Cl28 and C92Cl32: Evidence of the Existence of Three New Isomers of C96

Chlorination of various HPLC fractions of C₉₆ with a mixture of VCl₄ and SbCl₅ at 340–360 °C and single‐crystal X‐ray diffraction study of the products led to the identification of three new IPR isomers of C₉₆. The C₉₆(175) isomer forms a stable chloride, C₉₆(175)Cl₂₀, while chlorides of two other new isomers, C₉₆(114) and C₉₆(80), undergo cage shrinkage yielding C₉₄(NC1)Cl₂₈ and C₉₆(NC2)Cl₃₂ with non‐classical (NC) cages. These two NC chlorides contain, respectively, one and two heptagons flanked by pairs of fused pentagons and are stabilized by chlorine attachment to the emerging pentagon–pentagon junctions. Thus, the number of the experimentally confirmed C₉₆ isomers has reached nine, which corroborates the empirical rule that the C_6n fullerenes exhibit particularly rich isomerism.     

New Thioantimonates(III) with Different Sb:S Ratios: Solvothermal Syntheses and Crystal Structures of [(C3H10NO)(C3H10N)][Sb8S13], [(C2H8NO)(C2H8N)(CH5N)][Sb8S13], [(C6H16N2)(C6H14N2)][Sb6S10], and [C8H22N2][Sb4S7]

Four new thioantimonates(III) with compositions [(C₃H₁₀NO)(C₃H₁₀N)][Sb₈S₁₃] ( 1 ) (C₃H₉NO = 1‐amino‐3‐propanol, C₃H₉N = propylamine), [(C₂H₈NO)(C₂H₈N)(CH₅N)][Sb₈S₁₃] ( 2 ) (C₂H₇NO = ethanolamine, C₂H₇N = ethylamine, CH₅N = methylamine), [(C₆H₁₆N₂)(C₆H₁₄N₂)][Sb₆S₁₀] ( 3 ) (C₆H₁₄N₂ = 1,2‐diaminocyclohexane) and [C₈H₂₂N₂][Sb₄S₇] ( 4 ) (C₈H₂₀N₂ = 1,8‐diaminooctane) were synthesized under solvothermal conditions. Compound 1 : triclinic space group P$\bar{1}$ , a = 6.9695(6) Å, b = 13.8095(12) Å, c = 18.0354(17) Å, α = 98.367(11), β = 96.097(11) and γ = 101.281(11)°; compound 2 : monoclinic space group P2₁/m, a = 7.1668(5), b = 25.8986(14), c = 16.0436(11) Å, β = 96.847(8)°; compound 3 : monoclinic space group P2₁/n, a = 11.6194(9), b = 10.2445(5) Å, c = 27.3590(18) Å, β = 91.909(6)°; compound 4 : triclinic space group P$\bar{1}$ , a = 7.0743(6), b = 12.0846(11), c = 13.9933(14) Å, α = 114.723(10), β = 97.595(11), γ = 93.272(11)°. The main structural feature of the two atoms thick layered [Sb₈S₁₃]^2– anion in 1 are large nearly rectangular pores with dimensions 11.2 × 11.7 Å. The layers are stacked perpendicular to [100] to form tunnels being directed along [100]. In contrast to 1 the structure of 2 contains a [Sb₈S₁₃]^2– chain anion with Sb₁₂S₁₂ pores measuring about 8.9 × 11.5 Å. Only if longer Sb–S distances are considered as bonding interactions a layered anion is formed. The chain anion [Sb₆S₁₀]^2– in compound 3 is unique and is constructed by corner‐sharing SbS₃ pyramids. Two symmetry‐related single chains consisting of alternating SbS₃ units and Sb₃S₃ rings are bound to Sb₄S₄ rings in chair conformation. Finally, in the structure of 4 the SbS₃ and SbS₄ moieties are joined corner‐linked to form a chain of alternating SbS₄ units and (SbS₃)₃ blocks. Neighboring chains are connected into sheets that contain relatively large Sb₁₀S₁₀ heterorings. The sheets are further connected by sulfur atoms generating four atoms thick double sheets.     

Unimolekulare CH3-, CH4-, C2H4- und C3H4-Eliminierungen aus alkin- und arylsubstituierten Isopropylkationen in der Gasphase

Elimination of methyl, methane, ethylene, allene (or propyne) from two [C₃H₆Y]+ isomers (Y = p-(HC?C)? C₆H₄- and C₆H₅? C?C?) has been investigated using 13C and deuterium labelled compounds. It can be shown that the fragmentations are accompanied by extensive but not complete rearrangement of the carbon skeleton as well as by migration of the hydrogen atoms, the extent of which is determined by the reaction channel.     

A Nonempirical Quantum-Chemical Study and Natural Bond Orbital Analysis of C6H5XCY3 Species (X = SO or SO2, Y = H or F)

The potential functions of internal rotation about the C² _sp—S bonds for C₆H₅XCY₃ species (X = SO or SO₂, Y = H or F) have been obtained at the MP2 (full)/6-31+G(d) level of ab initio theory. It is found that the spatial structures with the plane of C² _sp—S—C³ _sp bonds, which is near perpendicular to the benzene ring plane, are the energy-favourable conformations. The values of the rotational barrier about the C² _sp—S bond are equal to (kJ/mole): 21.2 (C₆H₅SOCH₃), 29.0 (C₆H₅SOCF₃), 20.4 (C₆H₅SO₂CH₃), and 28.2 (C₆H₅SO₂CF₃). On the basis of the Natural Bond Orbital (NBO) analysis results, it has been revealed that the double S=O bond is a strongly polarized covalent -bond, whereas -bond electrons practically are localized on the oxygen atom. The S=O bond order for aromatic sulfoxides and sulphones is mainly caused by hyperconjugational interactions according to the LP(O) ^*(S—C_ipso) and LP(O) ^*(S—C _Y ) mechanisms. In sulphones there is also the additional mechanism of hyperconjugational interactions such as LP(O^{1 *}(S—O²) and LP(O²) ^*(S—O¹). With the replacement of one hydrogen atom on the —XCY₃ group, the charge loss of the unsubstituted benzene molecule increases: —SOCH₃ < —SO₂CH₃ < — SOCF₃ < —SO₂CF₃. The substitution of the —CH₃ group for the —CF₃ group weakly influences the charge value on the sulfur atom but effects the acceptor characteristics of the substituent to a greater extent than the variation of the sulfur atom coordination.     

Theoretical study on the HACA chemistry of naphthalenyl radicals and acetylene: The formation of C12H8, C14H8, and C14H10 species

The hydrogen-abstraction-C₂H₂-addition (HACA) chemistry of naphthalenyl radicals has been studied extensively, but there is a significant discrepancy in product distributions reported or predicted in literature regarding appearance of C₁₄H₈ and C₁₄H₁₀ species. Starting from ab initio calculations, a comprehensive theoretical model describing the HACA chemistry of both 1- and 2-naphthalenyl radicals is generated. Pressure-dependent kinetics are considered in the C₁₂H₉, C₁₄H₉, and C₁₄H₁₁ potential energy surfaces including formally direct well-skipping pathways. On the C₁₂H₉ PES, reaction pathways were found connecting two entry points: 1-naphthalenyl (1-C₁₀H₇) + acetylene (C₂H₂) and 2-C₁₀H₇ + C₂H₂. A significant amount of acenaphthylene is predicted to be formed from 2-C₁₀H₇ + C₂H₂, and the appearance of C₁₄H₈ isomers is predicted in the model simulation, consistent with high-temperature experimental results from Parker et al. At 1500 K, 1-C₁₀H₇ + C₂H₂ mostly generates acenaphthylene through a formally direct pathway, which predicted selectivity of 66% at 30 Torr and 56% at 300 Torr. The reaction of 2-C₁₀H₇ with C₂H₂ at 1500 K yields 2-ethynylnaphthalene as the most dominant product, followed by acenaphthylene mainly generated via isomerization of 2-C₁₀H₇ to 1-C₁₀H₇. Both the 1-C₁₀H₇ and 2-C₁₀H₇ reactions with C₂H₂ form some C₁₄H₈ products, but negligible phenanthrene and anthracene formation is predicted at 1500 K. A rate-of-production analysis reveals that C₁₄H₈ formation is strongly affected by the rates of H-abstraction from acenaphthylene, 1-ethynylnaphthalene, and 2-ethynylnaphthalene, so the kinetics of these reactions are accurately calculated at the high level G3(MP2,CC)//B3LYP/6-311G^** level of theory. At intermediate temperatures like 800 K, acenaphthylene + H are the leading bimolecular products of 1-C₁₀H₇ + C₂H₂, and 1-acenaphthenyl radical is the most abundant C₁₂H₉ isomer due to its stability. The predicted product distribution of 2-C₁₀H₇ + C₂H₂ at 800 K, in contrast to the results of Parker et al is predicted to consist primarily of species containing three fused benzene rings—for example, phenanthrene and anthracene—as the leading products, indicating HACA chemistry is valid from two to three ring polycyclic aromatic hydrocarbons under some conditions. Further experiments are needed for validation.     

Reverse Saturable Optical Absorption of C60, Soluble Methanofullerenes, and Fullerodendrimers in Sol-Gel Mesoporous Silica Host Matrices

Porous sol-gel glasses with various pore size distributions are prepared and either impregnated with pure C₆₀ or soaked with methanofullerenes or fullerodendrimers derivative solution. Induced absorption or reverse saturable absorption (RSA) has been studied in both types of solid materials. The samples impregnated by pure C₆₀ mainly contain well-dispersed fullerene molecules. Unlike crystalline films of C₆₀, their absorption dynamics can be well described by a 5-level model, developed for non-interacting C₆₀-molecules in solutions. Methanofullerene samples, on the other hand, show signs of micellar aggregation and therefore RSA dynamics, which are influenced by solid state effects. Fullerodendrimers derivatives lead to the highest quantum yield.     

DFT Study on the Bilaye Pentaprismane C15H10

A bilayer pentaprismane C15H10 formed by two pentaprismane cages sharing the same pentagon has been studied at the B3LYP/6-31G level.     

Aromatic stability energy studies on five-membered heterocyclic C4H4M (M = O, S, Se, Te, NH, PH, AsH and SbH): DFT calculations

Energetic, geometric and magnetic criteria were applied to examine the stability and/or aromatic character for the cyclic molecules C ₄ H ₄ M (M = O, S, Se, Te, NH, PH, AsH and SbH) at B3LYP/6-311++G^** and MP2/6-311++G^** levels of theory. The isodesmic reactions and nuclear independent chemical shifts (NICS) calculations were utilized to examine the molecules for energetic and magnetic criteria, respectively. The isodesmic reaction energies reveal that thiophene (C ₄ H ₄ S, ?23.269 kcal/mol) and pyrrole (C ₄ H ₄ NH, ?20.804 kcal/mol) have the greatest aromatic stabilization energies and tellurophene (C ₄ H ₄ Te, ?15.114 kcal/mol) and stibole (C ₄ H ₄ SbH, ?1.169 kcal/mol) have the lowest aromatic stabilization energies in their corresponding groups at MP2/6-311++G^**. The NICS calculations confirmed the results obtained through isodesmic reaction energies.