Linear free energy relationships for carbon-13 NMR chemical shifts of substituted benzoic acids1

In order to examine ¹³C-SCS of substituted benzoic acids, chemical shifts of the acid form (I) and the dissociated form (II) have been obtained separately. Single substituent parameters, σ⁰ or σ⁺ are correlated with the shifts for the carboxyl (δ_co) or ipso carbons (δ_ipso), respectively. Among the available five equations which are developed for the analysis with dual (or divided) substituent parameters (DSP), the Swain-Lupton equation (eqn 3) and the Taft-Swain-Lupton equation (eqn 4) give much better correlations, not only for δ_co and δ_ipso but also for the results for ring carbons (C(2), C(5), C(6)), except for those attached to or neighboured by substituents. It is concluded that the SCS of aromatic compounds are best analyzed with substituent parameters derived from reactions or equilibria on the basis of linear free energy relationships.     

π-Electronic structure of polymethines1

Polymethines are chain molecules with equal bond-lengths and charge alteration along the chain. They embrace three classes of compounds with (N - 1)π, Nπ, or (N + 1)π electrons on N atoms. The MO-theoretical characteristics of the (N - 1)π, Nπ, and (N + 1 )π polymethines are strongly related, and the eigenvalues can be derived by a mnemonic technique. The theoretical results establish the particular position of the polymethines among the π-systems and allow a rationalization of experimental findings within the framework of the one electron theory.     

The vibrational structure of NO+(X 1Σ+) from charge-exchange mass spectrometry

Charge-exchange mass spectrometry has been used to detect the first five vibrationl levels of the electronic ground-state ion NO^?(X ¹Σ^?). The absolute charge-exchange cross sections between thermal NO gas and 33 positive ions of 10 eV kinetic energy are given.     

The electronic structure of CrO3+ and MoO3+ complexes

The results of ab initio molecular orbital calculations for [CrOf_s]^2? and polarised single crystal electronic spectra of [MoOCl₃(Op(NMe₂)₃)₂] and Ph₄As[MoOCl₄(H₂O)] are presented. These data are consistent with the electronic transitions of the MO³⁺ moieties, O_2pπ → M_dxy and M_dxy → Md_dxy,dyz being the lowest energy transitions in the spectra of their respective complexes, both these transitions being of low intensity.     

BF分子X1∑+,A1∏和B1∑+电子态的势能函数

使用SAC/SAC-CI和D95++,6-311++g,6-311++g**及D95(d)基组,分别对BF分子的基态X1∑+、第一简并激发态A1∏和第二激发态B1∑+的平衡结构和谐振频率进行优化计算.对所有计算结果进行比较,得出6-311++g**基组为最优基组.运用6-311++g**基组和SAC方法对基态X1∑+,SAC-CI方法对激发态A1∏和B1∑+进行单点能扫描计算,并用正规方程组拟合Murrell-Sorbie函数,得到相应电子态的势能函数解析式,由得到的势能函数计算了与X1∑+,A1∏和B1∑+态相对应的光谱常数,结果与实验数据较为一致.     

Rotational analysis of the a3Π0+,1-X1Σ+ emission systems of GeH+

New emission systems have been observed from the helium afterglow reaction of GeH₄ in the 520–610 nm region. On the basis of the rotational analysis, they were assigned to the a ³Π_0⁺-X¹Σ⁺ and a³Π₁-X¹Σ⁺ subsystems of GeH⁺. Spectroscopic constants have been determined for the GeH⁺ (a³Π_0⁺, a³Π₁, X¹Σ⁺) states.     

Asymmetrical nitrogen-40;1 Geminal systems-261 N-chlorohydrazines3

The factors determining the kinetic and thermodynamic stabilities of N-chlorohydrazines are discussed. Acyclic N-chlorohydrazines exist only as trialkyldiazenium chlorides 3a,b. Chlorination of 2-acyl-1, 1-dimethylhydrazines 6a,b gave 1,4-diacyl-2,3-dimethylhexahydro-1,2,4,5-tetrazines 7a,b via hydrazyl radical intermediates, and chlorination of a 1-phenylpyrazolidin-5-one 8 gave phenylazoisovaleric esters 9a,b. Stable N-chlorohydrazines were obtained from bicyclic hydrazines; viz. the 2-chloro-1,2-diazabicyclo [2.2.2]octan-3-one 12 and 7-chloro-1,7-diazabicyclo[2.2.1]heptane 16. The restricted inversion of N(7) in 16 and its 1-methyl quaternary salt 21 were observed in the ¹³C-NMR spectra. The acyclic N-chloro-hydrazinium salt 25 was isolated.     

The structure of H3O+TiF5−

Oxonium pentafluorotitanate was prepared by the reaction of H₂O with TiF₄ in HF. Single crystal x-ray diffraction studies on H₃O⁺TiF₅- show that the compound crystallizes in monoclinic form. The space group is C2/c and the unit cell dimensions are a = 14.528(5), b = 4.839(1), c = 13.798(5)A^o α = 115.59(5)^o with 8 formula units per unit cell.     

Microwave spectrum and molecular structure of arsenic tribromide1

The microwave spectrum of arsenic tribromide has been recorded in the frequency range 26.5–40.0 GHz. From the rotational constants for the symmetric top species ⁷⁹AsBr₃ and ⁸¹AsBr₃ the following structural parameters have been deduced: r_z(AsBr) = 2.324 ± 0.003 Å, θ_z(BrAsBr) = 99.8 ± 0.2°. These results are in excellent agreement with the parameters obtained by Samdal et al., in a concurrent electron diffraction study.     

The pair polarizabilities of Li+/Li+ and Cl−/Cl−

Ab initio SCF MO energies and pair polarizabilities are reported for the pairs Li⁺/Li⁺ and Cl^?/Cl^? over the ranges of internuclear separation which are of importance in molten LiCl. The shapes of the β(R) curves resemble those of inert gas diatoms. The Cl^?/Cl^? interaction is predicted to make a rather small contribution to those properties of molten LiCl which depend on $\text{α}$⁽²⁾(R), and a larger contribution to properties which depend on β(R). The Li⁺/Li⁺ interaction contributes almost nothing to the bulk polarizability.     

The electronic structure of N4O62+ and the bonding interaction of NO+ and NO3−

The results are reported of an MO-SCF-CNDO/2 study of the experimental and optimal geometries of the N₄O₆²⁺ion cluster. The calculations are shown to support the stable existence of the N₄O₆²⁺ complex and the suggestion of its discoverers [1] on the role of NO⁺ in the N₂O₄ solutions. The proposed interpretation of the bonding interaction explains why the shortest N β O distances are found with the NO⁺ ions which have their nitrogen atoms displaced out of the NO₃^? plane.     

Potential energy curve of 1Σ+ Li+/He

The potential energy curve of the system Li⁺/He has been determined with moderately large basis sets for 0.5 ? r ? 10.0 a₀ both at the SCF level and including correlation. The present SCF results predict a deeper well (?0.00248 au) at a smaller r(3.66 a₀) compared with earlier calculations. Correlation deepens the well further (?0.00274 au), but pulls it inward slightly (3.63 a₀). In the repulsive part the calculated curve lies above the experimental one, especially at shorter distances. A similar behavior has been noted in the systems Li⁺/H₂, Li⁺/CO and Li⁺/N₂, suggesting that the experimental determinations may underestimate the interaction in this region by 10–20%.     

The crystal and molecular structure of 3,4-quinoxalino-1-telluracyclopentane C10H8N2TeII

The crystal and molecular structure of 3,4-quinoxalino-1-tellura(II)cyclopentane has been determined by X-ray diffraction at room temperature. The crystals are tetragonal, space group I4₁/a with a = b = 25.315(8), c = 6.010(1) Å and V = 3851.38 ų. The density of 1.96 g cm^?3 calculated on the basis of 16 molecules per unit cell is in agreement with the flotation value of 1.91 g cm^?3. The structure has been refined to a conventional R value of 0.0408 using 744 independent observed reflections obtained from four-circle diffractometer measurements. The structure consists of discrete molecules TeC = 2.134 Å (av.), CN = 1.343 Å (av.) and angle CTeC = 80.7° (e.s.d. 0.5) but the intermolecular TeTe bonds (3.791 and 3.998 Å) are less than the sum of the Van der Waals' radii thus indicating the presence of secondary bonding. These short intermolecular contacts in the crystal structure are consistent with the anomalous physical properties observed.     

BF分子X1Σ＋, A1P和B1Σ＋态的势能函数

使用SAC/SAC-CI和D95＋＋, 6-311＋＋g, 6-311＋＋g**及D95(d)基组, 分别对BF分子的基态X¹Σ^＋、第一简并激发态A¹Π和第二激发态B¹Σ^＋的平衡结构和谐振频率进行优化计算. 对所有计算结果进行比较, 得出6-311＋＋g**基组为最优基组. 运用6-311＋＋g**基组和SAC方法对基态X¹Σ^＋, SAC-CI方法对激发态A¹Π和B¹Σ^＋进行单点能扫描计算, 并用正规方程组拟合Murrell-Sorbie函数, 得到相应电子态的势能函数解析式, 由得到的势能函数计算了与X¹Σ^＋, A¹Π和B¹Σ^＋态相对应的光谱常数, 结果与实验数据较为一致.     

Electric moments,polarizabilities and hyperpolarizabilities for BH(X1Σ+ and CH+ (X1Σ+)

The electric moments and static polarizabilities of BH(1σ²2σ²3σ², X¹Σ⁺) and CH⁺ (1σ²2σ²3σ², X¹Σ⁺) were calculated at the experimental internuclear separation in the LCAO SCF MO approximation. Most of the molecular properties reported in this paper for BH and CH⁺ appear for the first time and should be close to the Hartree—Fock limit. All tensors up to the fourth rank have been included in this study. The isotropy and anisotropy of the α, β and γ tensors are, in atomic units. $\text{α}$ = 22.71, Δα = ?0.26, $\text{β}$ = 55.1, Δβ = ?183.7, $\text{γ}$ = 12428, Δ₁γ = 37895, Δ₂γ = 25120 for BH and $\text{α}$ = 7.73, Δα = 0.39, $\text{β}$ = ?12.4, Δβ = ?11.7, $\text{γ}$ = 344, Δ₁γ = 1515, Δ₂γ = 750 for CH⁺.     

The first two excited 1Σg+ states of Cs2

Laser-induced fluorescence Of Cs₂ molecules in the infrared region (4000–9000 cm^?1) has been observed using several exciting wavelengths from an argon-ion laser and from a ring dye laser. Accurate molecular constants for the first two excited ¹Σ_g⁺ electronic states are derived from spectra recorded at high resolution by Fourier transform spectroscopy. Main molecular constants are: (2)¹Σ_g⁺: T_c = 12114.090 cm^?1, ω_e = 23.350 cm^?1, B_c = 7.4.5 × 10^?3 cm^?1, R_c = 5.8316 Å; (3)¹Σ_g⁺: T_e = 15975.450 cm^?1, ω_e = 22.423 cm^?1 , B_e = 8.23 × 10^?3 cm^?1, R_c = 5.5569 Å.     

Palladium-catalyzed syntheses of condensed cyclopentanes. The crystal and molecular structure of 3-benzylidenpentacyclo[9.2.1.5,8.11,11.02,10.04,9]-pentadecane

New syntheses of condensed cyclopentanes are described, based on insertion into a sufficiently stable PdC bond of molecules able to provide an easy reductive elimination step. These reactions are highly stereoselective. Interesting features are revealed by the X-ray investigation of the title compound, which was obtained in good yield from β-bromostyrene and norbornene. The structural parameters are reported; the molecule adopts the conformation with the bridging carbon atoms of the two norbornanes trans with respect to the mean plane of the cyclopentylidene ring. The condensed cyclopentane system is highly symmetric. The phenyl group is twisted out of the plane of the cyclopentylidene ring by 25.3°.     

A 1Π ← χ1Σ+ resonance-enhanced multiphoton ionization of jet-cooled CO

We report the observation of two-photon resonance enhancement in the four-photon tunable dye laser-induced multiphoton ionization spectrum of CO. The observed structure is readily assigned to the rotational bands of the A ¹Π ← χ¹Σ⁺ (3,0) transition of CO.     

The photodissociation of CH+ through absorption into the A1Π state

Cross sections for the photodissociation of ground state CH⁺ ions through absorption into the A¹Π state are calculated for the lowest three vibrational levels. At threshold the cross sections for υ″ = 0, 1 and 2 are respectively 5.0 × 10^?20 cm², 8.1 × 10^?19 cm² and 2.6 × 10^?18 cm².