Extension de la reaction de Wittig: Condensation “d'ylures enolates” sur les cetones aliphatiques

The enolate ylide Ph₃P⁺C^?C(Ph)O^?Li₊ obtained by the reaction of HMPT-Li with the benzoylmethylenetriphenylphosphorane Ph₃PCHCOPh reacts with aliphatic ketones, in contrast to its precursor. This condensation makes it possible to prepare β,γ-unsaturated ketones, of type RCHC(R′)CH₂COPh, instead of the α,β isomer usually obtained in a Wittig reaction.     

On the structures of alpha-lithiated sulfoxide,sulfone and sulfonium systems. Implications for the stereochemistry of functionalization of carbon atoms adjacent to sulfur

The fully optimized geometries of C-S torsional isomers of LiCH₂SHO, LiCH₂SHO₂, and LiCH₂SH₂⁺ have been computed at the 3–21G^* level. The global minima of the sulfoxide and sulfone contain intramolecular LiO bonds. In the presence of Li⁺, intermolecular LiO bonding alters the structure of the alpha-lithiated sulfoxide, and the CLi bond is antiperiplanar to oxygen. The alpha-lithiated sulfonium cation exhibits no unusual conformational features, and a low barrier to CS torsion. The implications of these results upon the stereochemistry of functionalization of a carbon atom adjacent to sulfur by a lithiation-quenching sequence are discussed.     

Photochemistry of metalmetal bonded complexes.: IV. Breaking of the metalmetal bond and decoupling of the two 1,4-diaza-1,3-butadiene (= R-DAB) fragments of bis(1-t-butylimino-2-t-butylaminoethane) (= t-Bu-IAE) during the photochemical conversion of Mo2(CO)6(t-Bu-IAE) into Mo2(CO)6(t-Bu-DAB)2

The complex Mo₂(CO)₆(t-Bu-IAE) (I) (bis(1-t-butylimino-2-t-butylaminoethane) which contains a MoMo bond and a tetradentate 10e donor ligand t-Bu-IAE, consisting of two CC coupled t-Bu-DAB (t-BuNCHCHNBu-t) ligands has been irradiated into its σ → σ^* transition. The photolysis yields Mo₂(CO)₆(t-Bu-DAB)₂ (II), a complex in which the MoMo bond is broken and the uncoupled t-Bu-DAB ligands act as 6e (σ-N,μ²-N′,η²-CN′) donors.     

Electronic structure of the 1,3-butadiyne anion studied by electron transmission and vibrational excitation spectra in the gas phase

The electron transmission and vibrational excitation spectra of the title compound are reported. Two bands, at 1.0 and 5.6 eV are found in the ETS spectrum. The 1.0 eV resonance excites mainly the CC stretch vibration ν₂ and the CH bend vibrations ν_6,8 in even quanta. It has been assigned to the ²Π_u (in linear geometry) ground state of the anion. This state is found to be bent in the equilibrium geometry and the minimum of the anion potential surface lies outside of the Franck-Condon region. The band around 5.6 eV is interpreted as the ²Π_g resonance overlapping with a σ^* resonance which excites mainly the CH stretch vibration ν₁. A remarkable feature is the excitation of high levels of the CH bend vibration near threshold, with E_r ? 0.3 eV.     

Studies of the characteristic frequencies of vapor-phase infrared spectra: II. The characteristic frequencies of ketones and aldehydes

Vapor-phase infrared characteristic frequencies of ketones and aldehydes have been studied. The CO stretching vibrations in vapor phase have higher frequencies than those in condensed phase. The shifts are about 20 cm⁻¹ for ketones and about 10 cm⁻¹ for aldehydes. Both ketone and aldehyde have an absorption band at the range 1300–1100 cm⁻¹, although their intensities are very different. This band was assigned to the CC stretching vibration of C(CO)unit.     

Power-gap law and the dynamical constraints on angular momentum transfer in rotationally inelastic molecular collisions

The model proposed by Dexheimer, Durand, Brunner and Pritchard has been developed and tested on CO₂H₂, CO₂He, Na₂He, Na₂Ne and N₂Ar. This model explains the rapid decrease in the rotationally inelastic integral cross sections with increase in the amount of rotational energy transfer (∣ΔE∣) in the region ∣ΔE∣ > ∣ΔE∣^*, ∣ΔE∣^* is foun to depend on the reduced mass of the system, the moment of inertia of the molecule, the initial rotational state, and the interaction potential. Data for the systems studied show quantitative agreement with the predictions of the model.     

Surface-hopping model for near-resonant electronic energy transfer

A surface-hopping model is applied to near-resonant electronic energy transfer in the NFBi and O₂I systems. Multiple surface crossings occur in NFBi at ca. 8 A, corresponding well with measured transfer cross section of 200 A². A Landau-Zener model yields the temperature dependence of the thermally averaged cross section for the laser pumping reaction, O^*₂(a¹Δ) + I(²P_{$\text{3}\text{2}$}) → O₂(X³Σ^?_g) + 1^*(²P_{$\text{1}\text{2}$}).     

The oriented C2Cl6− radical in irradiated hexachloroethane single crystals: An EPR and molecular-orbital study

The C₂Cl₆⁻ radical has been detected by EPR methods in X-ray irradiated C₂Cl₆ crystals at 77 K. The radical, which decays rapidly upon exposure to visible light at 77 K, retains the staggered configuration of C₂Cl₆ and exhibits a structure in which the directions of the largest chlorine hyperfine tensor component and smallest component of the g-tensor occur close to the CC bond direction. In contrast, an INDO calculation predicts that the largest unpaired electron density occurs along the CCl bond direction and the CCl bond length increases by 0.4 Å upon electron addition.     

1,3-Oxaphospholane

sec. 2-Hydroxyalkylphosphines of the general formula R¹PHCH₂CHR²OH react with aldehydes and ketones forming 1,3-oxaphospholanes. The mechanism of this cyclization-reaction as well as the chemical behaviour of this new class of PO-heterocyclic compounds—especially the oxydation to P-oxides or P-sulfides, the formation of phosphonium salts and the hydrolytic cleavage of the ring is discussed.     

Etude structurale de composes organosilicies par diffusion rayleigh depolarisee : V. Proprietes acceptrices d'electrons du silicium dans les systemes SiOC et SiOSi

Among the characteristic properties of the SiOC and SiOSi systems relative to those of the corresponding COC systems, the optical anisotropy is a new example which shows the electron-acceptor ability of silicon by (p → d)π interaction in compounds of the type R₃SiO∑ (R = Me, Et, Pr; ∑ = H, Me, SiMe₃, CH₂-t-Bu, CHMe₂, CMe₃). Effectively, the existence of a linear relationship between the optical anisotropy or the principal optical polarisabilities of the OSiR₃ groups and the Taft's parameter σ^★ of the ∑ groups in this series of compounds, shows that the electron-accepting character of silicon increases with increasing electron-donating ability of the group ∑; this relationship simultaneously translates an increase of the electronic density and mobility perpendicular to the OSi axis to the detriment of the parallel direction. In application, we calculated the σ^★ values for the groups ∑ = SiEt₃, SiPr₃ and the OSiMe₃ optical anisotropy value in PhOSiMe₃.     

Formation and molecular structure of permethylyttrocene methyl tetrahydrofuranate

The reaction of Cp^*₂YCl·THF with MeLi in THF at −80°C gives the monomeric Cp^*₂YMe·THF (1), which has been characterized by spectroscopy, elemental analyses and a single crystal X-ray diffraction study. Complex 1 crystallizes in the orthorhombic space group Pnam with lattice parameters a 17.881(4), b 8.621(2), c 15.095(3) Å, Z = 4, and D_calc 1.274 g cm⁻³. Least-squares refinement using 1056 independent observed reflections and 117 parameters gave a final R value of 0.071. The YC(σ) bond distance is 2.44(2) Å. IR and NMR spectra indicate an agostic interaction between the metal center and one of the CH bonds of the methyl ligand, but this could not be confirmed by the X-ray structure determination owing to disorder.     

Stereoregularity of poly(alkyl α-chloroacrylates) and mechanism of isotactic polymerization

The catalytic activity of the complexes prepared by the reaction of Grignard reagents with ketones, esters, and an epoxide as polymerization catalysts of methyl and ethyl α-chloroacrylates was investigated. The modifiers which gave isotactic polymers were α,β-unsaturated ketones such as benzalacetophenone, benzalacetone, dibenzalacetone, mesityl oxide, and methyl vinyl ketone, and α,β-unsaturated esters such as ethyl cinnamate, ethyl crotonate, and methyl acrylate. Catalysts with butyl ethyl ketone, propiophenone, and propylene oxide as modifiers produced atactic polymers but no isotactic polymers. It was revealed that the complex catalysts having a structure ? C?C? O? MgX (X is halogen) gave isotactic polymers. The mechanism of isotactic polymerization was discussed. In addition, for radical polymerization of ethyl α-chloroacrylate, enthalpy and entropy differences between isotactic and syndiotactic additions were calculated to give ΔH_i^* ? ΔH_s^* = 910 cal/mole and ΔS_i^* ? ΔS_s^* = 0.82 eu.     

The long-wavelength MCD of some quinones and its interpretation by semi-empirical MO methods

Long-wavelength MCD spectra of several quinones are measured in solution at a magnetic field strength of 5.26 T. The B terms for the ππ^* transitions are computed with wavefunctions of the PPP type. The results enable one to deduce the polarization of many of the ππ^* bands. The signals due to nπ^* transitions are identified with the help of CNDO calculations. A very weak long-wavelength A term appearing in the spectra of some of the compounds is identified as due to the S_OT₁ (³nπ^*) absorption.     

Gas-phase electron diffraction determination of the molecular structure of perfluoro(methyloxirane)

The molecular geometry of perfluoro(methyloxirane) has been studied using gas-phase electron diffraction data, effective least-squares refinement of the structure being achieved with the aid of constraints to limit the number of variable parameters. With the CCF₃ bond constrained to be 0.078 Å longer than the ring CC, the refined bond- length values CF (av.) = 1.323(2), CO (av.) = 1.410(8), and CC (ring) = 1.467(7) Å ($\text{r}$_g values, with e.s.d. in parentheses) were obtained; the angles between ring bonds and substituent CF bonds were CCF (av.) 121(1) and OCF (av.) 114(1)^o, the corresponding parameters involving the bulkier CCF₃ fragment being larger by 3^o in each case [∠CCCF₃ 124(1)^o∠OCCF₃ 117(2)^o]. The remaining refined parameters were ∠CCF(of CF₃) = 110.6(4)^o and τ , a torsion angle defining the orientation of the CF bonds of the CF₃ group with respect to ring bonds, = 29(2)^o. Dependent bond angles possessed the values 62.7 (COC), 58.7 [OCC (ring)], 108.3 [FCF (CF₃ group)], 114 [FCF (ring CF₂)], and 111^o (FCCF₃).     

Preparation de β-cetonitriles via l'acylation du cyanacetate de trimethylsilyle par les anhydrides mixtes.

β-ketonitriles R¹COCH₂CN and R¹COCH(R²)CN are respectively prepared from (CH₃)₃SiOCOCHLiCN or R²CHLiCN by acylation reaction with mixed anhydrides RCOOCO₂Et.     

Conversion from a π to a σ structure on replacing oxygen by sulphur: an ESR study

The radical cations of 1,3-dioxacylohexane and 1,3-dioxacyclopentane have π-structures involving delocalisation within the [-OCH₂O-]⁺ unit with high spin-density on the CH₂ group, whilst, in complete contrast, the corresponding sulphur derivatives have a weak σ bond between the two sulphur atoms, the unpaired electron being in the σ^* orbital with negligible spin-density on the CH₂ group.     

Preparation d'alcools acetyleniques et propargyliques F-alkyles

A number of α-β acetylenic carbinols R_FCCC(OH)RR′, in which the acetylenic proton was substituted by a F-alkyl group, were first prepared, from a classical reaction of (F-alkynyl)- lithium derivatives R_FCCLi upon various carbonyl compounds.On another hand, the reaction of propargyl bromide metallic complexes (organoaluminic, or ultrasonic irradiation activated organozinc) upon some polyfluorinated ketones R_FCOR led to the formation, in convenient yields, of the propargylic carbinols HCCCH₂C(OH)RR_F.The synthesis and properties of these series of new (F-alkyl) substituted acetylenic and propargylic alcohols are described and discussed.     

The T3 (π, π) State of acridine

The 00 band maximum of the transition T₃(π, π^*) ← T₁ (π, π^*) of acridine occurs at ≈ 10200 ± 20 cm^?1 in inert (n-hexane, benzene, CCl₄), at 10220 ± 20 cm^?1 in polar (acetonitrile) and at 10170 ± 50 cm^?1 in hydrogen-bonding (methanol, 2-propanol and alkaline water) solvents. Based on the solvent-independent energy of T₁ (π, π^*), the T₃(π, π^*) state of acridine is estimated at 26050 ± 50 cm^?1 in all the solvents.     

Novel unexpected examples of 5JHH long range couplings in carbohydrates.

⁵J_HH Couplings proceeding through a HCCCCH - fragment rather than a HCOCCH - path in certain L-idofuranose derivatives are described. The probable mechanism is discussed.     

Etude par RMN 13C Et 199Hg de composes oxobromo- et dioxomercuriques

Organomercuric compounds of the general formula

and [RCOCH(R′)]₂Hg, obtained from three ketones, 2,2-dimethyl 3-pentanone, 1-mesityl 1-propanone and 1-mesityl 1-ethanone, have been studied by ¹³C and ¹⁹⁹Hg NMR techniques. Coupling constants J(CHg) and J(HgH) are consistent with C-metalated species; in each case the values of δ(C(2)) and J(C(2)H) observed are higher than expected for purely sp³ carbon. The contribution of O-metalated species and hyperconjugative effects are discussed. For two dioxomercuric compounds (R′  Me, R  t-Bu, mesityl) the existence of diastereoisomers is suggested from ¹⁹⁹Hg NMR data.