Theoretical study on the optical activity of spiro[3.3]hepta-1,5-diene

The spectroscopic and chiroptical properties of the title compound 1 has been predicted and interpreted by a quantum mechanical approach using the CNDO-CI modification of Del Bene and Jaffé. The calculated rotational strength of the longest wavelength transitions according to the method of Hug and Wagnière suggests left-handed chirality for levorotatory 1. The assignment is in agreement with previous work. In addition, the same computational method has been employed for spiro[4.4]nona-1,6-diene (2) and spiro[4.4]nonatetraene (3).     

Infrared and Raman spectra of spiro[2.4]hepta-4,6-diene and [1,2-2H4]spiro[2.4]hepta-4,6-diene

The i.r. spectra of spiro[2.4]hepta-4,6-diene and of [1,2-²H₄]spiro[2.4]hepta-4,6-diene have been measured for gas and liquid samples, for carbon disulfide and carbon tetrachloride solutions, and for samples matrix isolated in argon, krypton or nitrogen. The Raman spectra with depolarization ratios were determined for both isotopic molecules. Vibrational assignments for all fundamental modes of both molecules are proposed based upon polarizations of Raman lines, isotopic frequency shifts, and group frequencies in comparison with vibrational assignments of cyclopentadiene, cyclopropane and d₆-cyclopropane.     

Dzhemilev reaction for the synthesis of spiro[3.3]heptane and spiro[3.4]octanes

For the first time cycloalumination of methylenecyclobutane with the aid of Et₃Al in the presence of Cp₂ZrCl₂ leading to 6-ethyl-6-aluminaspiro[3.4]octane has been realized. The latter, without isolation, was converted into spiro[3.3]heptane, 6-thiaspiro[3.4]octane and also spiro[3.4]octan-6-ol and 6-spiro[3.4]octyl formate with high yields and selectivity.     

Catalytic cyclopropanation of spiro[2.4]hepta-4,6-diene with diazomethane

Catalytic cyclopropanation of spiro[2.4]hepta-4,6-diene with diazomethane in the presence of copper or palladium compounds results in mono- and dicyclopropanation products, namely, spiro[bicyclo[3.1.0]hex-3-ene-2,1′-cyclopropane] and spiro[cyclopropane-1,5′-tricyclo[4.1.0.0^2,4]heptane], with different efficiency. The use of Pd compounds as catalysts allows the cyclopropanation to be performed under conditions of simultaneous generation and decomposition of diazomethane.     

Ring-opening reactions of spiro[2.4]hepta-4,6-diene and spiro[4.4]nona-1,3-diene induced by tungsten(0) carbonyls

Tungsten(0) carbonyls react with the strained spiro[2.4]hepta-4,6-diene and the less strained spiro[4.4]nona-1,3-diene with CC bond cleavage and formation of stable alkylene bridged π-cyclopentadienyl-σ-alkyl complexes. The product containing a two carbon bridge has the same unusual spectroscopic properties as the analogous molybdenum complex.     

Molecular ion LiHe: ab initio study

High level ab initio calculations are performed on the molecular ion LiHe⁺. Potential energy curves for the low-lying singlet and triplet electronic states are calculated using the multi-reference configuration interaction and single-reference coupled cluster methods with large basis sets. The corresponding dipole moments and transition dipole moments functions are also determined. The basic spectroscopic properties and excitation energies of the electronic states are derived from rovibrational bound state calculations.     

An ab initio molecular orbital study of Li2O2 and LiO2H

An ab initio molecular orbital study, using a Gaussian basis set, of the geometries of Li₂O₂ and LiO₂H is presented. Consistent with the experimental data available, Li₂O₂ is found to have a rhombic structure; the O-Li-O configuration in LiO₂H is found to form an acute triangle. The bonding in these species is discussed to terms of Mulliken population analyses.     

The formation of tetracyclo[7.2.1.02,5.02,8]dodeca-6,10-dienes under conditions of thermal isomerization of spiro[2.4]hepta-4,6-diene into bicyclo[3.2.0]hepta-1,3-diene

The formation of the novel hydrocarbons, tetracyclo[7.2.1.0^2,5.0^2,8]dodecadienes, as a result of thermal isomerization of spiro[2.4]hepta-4,6-diene into bicyclo[3.2.0]hepta-1,3-diene and its capture by 1,3-dienes is demonstrated. The conditions of thermal isomerization and dimerization of the spiroheptadiene are studied. Cyclopropanation of the polycyclic dienes formed by diazomethane in the presence of Pd-catalysts was accomplished, and occured solely through the norbornene double bond.For preliminary communication see ref.¹ Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 132–137, January, 1993.     

Ambiguousness of GC-MS identification of spiro[2.4]hepta-4,6-diene in natural objects

The publications on the GC-MS identification of spiro[2.4]hepta-4,6-diene in various natural objects were critically considered. Significant similarity of the mass spectra and coincidence of the GC retention indices on standard nonpolar phases of spiro[2.4]hepta-4,6-diene (761±3) and its isomer (toluene, 760±8) do not allow one to assert that the spirocyclic hydrocarbon was found in all the cases. Additional analytical parameters should be applied to differentiate such isomers.     

Molecular characterization and glassy-state properties of poly(spiro[2,4]hepta-4,6-diene)

Poly(spiro[2,4]hepta-4,6-diene) (PSHD) is a random copolymer composed of 1,2 and 1,4 units. Although PSHD has been reported to have a very large Sakurada–Mark–Houwink exponent (a = 1.71) characteristic of rigid rods, a new determination of the intrinsic viscosity–molecular-weight relation for fractionated samples with known copolymer composition gives a smaller value (0.81). The rigidity of the PSHD molecule was also investigated by calculations of the conformational energy associated with the main chain and the dynamic viscoelasticity associated with the molecular motion in a solid state. A sharp potential energy minimum occurs at a dihedral angle χ₁ = 260° in polymer composed of all trans 1,4 units. The dynamic loss tangent for the primary absorption decreases with increasing fraction of the 1,4 unit. These properties result from the characteristics of the stiff 1,4 unit sequences in the molecular chain. The density of PSHD decreases with increasing content of 1,4 units and was found to be considerably smaller than values for typical polymers, in relation to the occupied volume of the repeat unit. This fact can be explained by the peculiar aggregation state of molecular chains composed of rigid and flexible units.     

Nuclear magnetic resonance spectra of some 2,6-disubstituted spiro[3.3]heptane derivatives

Analysis of the full splitting pattern of the 100 MHz ¹H-NMR spectra of diethyl - 2,6 -dibromospiro[3.3]heptane - 2,6 - dicarboxylate (3) in chloroform and benzene and the 220 MHz ¹H-NMR spectrum of dimethylspiro[3.3]heptane - 2,6 - dicarboxylate (2) in naphthalene has been carried out. Puckering of the cyclobutane rings is revealed. Reasonable agreement with an X-ray study on Fecht acid (1) and with the data from the ¹C-NMR spectra of compounds 2 and 3 has been obtained. The temperature dependency of the ¹H-NMR spectra of 2, 3 and the symmetrically substituted tetraethylspiro[3.3]heptane - 2,2,6,6 - tetracarboxylate (4) has been investigated and is discussed in terms of conformational interconversion.     

Studies on polymers from cyclic dienes. XII. Cationic polymerization of spiro[2,4]hepta-4,6-diene

Polymerizations of spiro[2,4]hepta-4,6-diene were carried out with cationic initiators and Ziegler-type catalysts. This monomer polymerized very rapidly with a variety of cationic initiators, and low monomer and initiator concentrations had to be employed in order to avoid formation of crosslinked polymers. The polymer contained 1,2 and 1,4 addition units, and there was no indication of the opening of the cyclopropyl ring in the monomer unit. The following relationship was obtained: [η] = 4.5 × 10^?8M?_n^1.71. The exponential coefficient of this equation is much greater than those typical of vinyl polymers, suggesting that the polymer chain is very stiff. The polymer showed much enhanced resistance to autoxidation as compared with polycyclopentadiene, and its softening point was above 200°C. These interesting physical and chemical properties of the monomer and the polymer can be associated with their spiro structures.     

Ab initio molecular orbital study of dialuminum-ethylene complexes

The geometries of the various isomeric dialuminum-ethylene complexes Al₂C₂H₄ have been optimized using the STO-3G, 3-21G^(*) and 6-31G^(**) basis sets. Vibrational frequency calculations show that only two out of the six structures examined are thermodynamically stable. Unlike the case of Li₂C₂H₄, 1,2-dialuminoethane is most stable and more ethane-like than 1,2-dilithioethane perhaps due to the larger covalent character of the C---Al bond. Besides, 1,2-dialuminoethane has been found, in contrast to ethane and 1,2-dilithioethane, to have no stable gauche conformer.     

The Radical Cations of Bicyclo[2.2.1]hepta-2,5-diene (8,9,10-Trinorborna-2,5-diene) and bicyclo[2.2.2]octa-2,5-diene (2,3-Dihydrobarrelene). An ESR and ENDOR study

The radical cation of bicyclo[2-2.1]hepta-2,5-diene (8,9,10-trinorborna-2,5-diene; 1 ) in CF₂ClCFCl₂, and CF₃CCl₃ matrices and that of bicyclo[2.2.2]octa-2,5-diene (2,3-dihydrobarrelene; 2 ) in CFCl₃ and CF₃CCl₃ matrices have been studied by ESR and ENDOR spectroscopy. For ${\bf 1}^{+ \atop \dot{}}$, the coupling constants of the olefinic, methano-bridge, and bridgehead protons are ?0.780 ±0.005, +0.304±0.002, and ?0.049±0.002 mT, respectively. The hyperfine tensor for the methano-bridge protons is axial, A_x = +0.263 ± 0.002 and A_y = +0.386 ± 0.002 mT, while that for the olefinic protons is orthorhombic, A_x = ?0.594 ± 0.005, A_y= ?0.913 ± 0.005, and A_z = ?0.834 ± 0.005 mT (x parallel to C? H- z parallel to 2p_π axis). For ${\bf 2}^{+ \atop \dot{}}$, the coupling constants of the olefinic, ethano-bridge, and bridgehead protons are ?0.68 ± 0.01, +0.162 ± 0.005, and ?0.108 ± 0.005 mT, respectively. The hyperfine data for ${\bf 1}^{+ \atop \dot{}}$ and ${\bf 2}^{+ \atop \dot{}}$ fully support the presentation of their singly occupied orbitals as antisymmetric combinations, b₂(π), of the two bonding ethene π-MO's.