Empirical parameters of lewis acidity and basicity for aqueous binary solvent mixtures

Empirical parameters of Lewis acidity, E^N_T, introduced by Reichardt et al., and Lewis basicity, B_KT , introduced by Kamlet and Taft, have been determined for mixtures of water with ten organic solvents. In the case of water/alcohol mixtures a distinct dependence between these acidity and basicity parameters have been found. For the other solvent mixtures the E^N_T on B_KT dependence is more complex even if these parameters are purified from non-specific solute/solvent interactions.     

Asymmetric cyclization of unsaturated aldehydes catalyzed by a chiral lewis acid

A highly enantioselective cyclization of prochiral unsaturated aldehydes has been accomplished with a chiral zinc reagent derived from dimethylzinc and ($\text{R}$)-(+)-1,1′-bi-2-naphthol.     

New routes to heterocycles via sulphenylation of unsaturated amides

Reaction of manganic acetate with organic disulphides in dichloromethane-trifluoroacetic acid in the presence of a variety of unsaturated amides leads to intramolecular cyclisation with formation of sulphenylated oxazolines, oxazines or tetrahydropyrroles.     

Titanium-based lewis acids for living cationic polymerizations of vinyl ethers and styrene: Control of lewis acidity in design of initiating systems

This brief account discusses the development of HCl/TiCl_4-n(OR)_n (n = 1–4), the titanium-based new initiating systems for living cationic polymerizations of vinyl ethers and styrene. The focus of this development is controlling the Lewis acidity of the metal halide components [TiCl_4-n(OR)_n] or “activators” in relation to the structure of the monomers. Thus, for vinyl ethers, relatively mild Lewis acids such as TiCl(OiPr)₃ and TiCl₂(OiPr)₂ are effective, whereas for styrene, a stronger Lewis acid such as TiCl₃(OiPr) is employed along with an added salt (nBu₄N⁺Cl⁻). In both cases, living polymers of controlled molecular weights can be obtained in methylene chloride solvent at −15°C.     

Synthesis of phosphorus-substituted amides of unsaturated carboxylic acids containing PCHN fragment

Russian Journal of General Chemistry -     

Tandem conjugate addition-α-alkylation of unsaturated amides. Synthetic methodology.

1,4-Addition of RLi, RMgX, and (RS) ₂CHLi reagents to unsaturated amides 2a-c followed by α-alkylation is shown to constitute a general and efficient synthetic procedure for the formation of two CC bonds in a single step.     

An empirical relationship between the eluant strength parameter ε° and solvent lewis acidity and basicity

It has been found that Snyder's eluant strength parameter ε°, used in liquid-solid adsorption chromatography, can be well described by a complementary Lewis acid-base model for solute-solvent interactions: ε°=0.152+0.859 · E^N_T + 0.332 · B_KT(cf Eq.9), with a correlation coefficient of r = 0.949 for 28 solvents. This result is in agreement with the theoretical interpretation of ε° The correct statistical procedure for estimating the significance of added explanatory parameters in the sequential multiparameter regression analysis is shown (cf Appendix). A comprehensive list of improved Kamlet-Taft solvent basicity parameters, B_KT, is given.     

Torsional potential barriers in conjugated molecules: unsaturated N-substituted amides

A theoretical study on torsional potential barriers in diformamide and N-vinylformamide is described. The mutual influence between π bonds with respect to the conformational rigidity is discussed on the basis of ab initio and PEM (Partition of Energy Method) calculations.The introduction of unidimensional torsional potentials in the PEM scheme provided good agreement with the ab initio results.     

O-attack versus N-attack: electrophilic halocyclization of unsaturated amides with vinylic halogen substitution

Electrophilic iodocyclization of unsaturated amides with an internal vinylic halogen (Cl, Br, or I) substitution afforded exclusively the corresponding cyclic iminoketones via iodolactamization. On the other hand, amides having a terminal vinylic halogen substituent underwent iodolactonization only. Theoretical calculations revealed that the iodocyclization proceeds via the intramolecular iodonium ion transfer from the amide nitrogen to the C=C double bond.     

Hydride affinities of borane derivatives: novel approach in determining the origin of lewis acidity based on triadic formula

The problem of intrinsic Lewis acidities of simple boron compounds (BH3-mXm, m = 0-3, X = F, Cl, Br, CH3, and OH) is assessed by their gas-phase hydride affinities (HAs). A simple and intuitively appealing picture of the interaction process including detachment of an electron from the hydride ion H-, capture of the pruned electron to the investigated Lewis acid (LA), and subsequent formation of the homolytic chemical bond between two newly created radicals is proposed. It enables transparent and straightforward dissection of the initial and final state effects, which taken together with the intermediate relaxation stabilization determine the trend of changes in the hydride affinities. The former effect is reflected in the electron affinities of the neutral Lewis acids given within Koopmans' approximation, while the final state effect involves properties of the formed Lewis acid-base adducts mirrored in the bond dissociation energy of the formed [LA-H]- chemical bond. It is demonstrated that unexpectedly low Lewis acidity of fluoroboranes relative to the corresponding chlorine and bromine derivatives can be traced down to the unfavorable Koopmans' electron affinities. Hence, it is a consequence of the initial state effect. In contrast, chloroboranes are more potent Lewis acids than fluoroboranes, because the relaxation and final state effects decisively influence their Lewis acidity. Finally, bromine-substituted borane compounds provide the most powerful studied Lewis acids. Their hydride affinities are result of a synergic interplay of the initial state, intermediate stabilization via relaxation, and final state effects. It is shown that Pearson's global hardness indices defined within his hard and soft acid-base (HSAB) principle fail to adequately predict and interpret the calculated hydride affinities.     

Tandem conjugate addition-α-alkylation of unsaturated amides. Synthesis of 1-aryltetralin lignans

The amide alcohols, obtained in one step from the sequential reaction of N,N-dimethylcrotonamide with dithiane anion and aryl aldehyde, were efficiently converted into the lignans galcatin and isogalcatin.     

Deoligomerization: a new route to lactams from unsaturated amides via radical oligomerization

[reaction: see text] Triethylborane-initiated atom transfer radical oligomerization of N-allyl or N-(3-butenyl)iodoacetamides followed by treatment with hydrochloric acid and subsequent neutralization with K(2)CO(3) led to the formation of the corresponding 5-hydroxyl-substituted delta-lactams or caprolactams, respectively. This oligomerization-deoligomerization sequence serves as an alternative to the corresponding intramolecular cyclization reactions.     

Regioselectivity and reactivity in the addition of trichloromethyl radicals to amides of unsaturated carboxylic acids

The AM1 method was used to analyze the factors that correlate with regioselectivity in the addition of radicals to 1,2-disubstituted unsaturated compounds. The rate constants of the addition of^.CCl₃ radicals to RCH=CHC(O)X (R = Ph, Me; X = N-pyrrolidyl) were determined by ESR. The analysis of the spin density distribution in mono- and 1,2-disubstituted alkenes and the experimental values for the rate constants of the addition of^.CCl₃ radicals to these alkenes allowed the authors to conclude that the efficiency of the addition of^.CC1₃ to unsaturated compounds depends only on steric effects.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 452–455, March, 1995.     

Fluorescence maxima of 10-methylacridone-metal ion salt complexes: a convenient and quantitative measure of lewis acidity of metal ion salts

Aromatic carbonyl compounds such as 10-methylacridone form the Lewis acid complexes including paramagnetic and redox active Lewis acids. The fluorescence energies of the Lewis acid complexes are well correlated with the O2*--Lewis acid complexes derived from the gzz-values of the ESR spectra of the superoxide anion-Lewis acid complexes, thus providing a quantitative measure of the Lewis acidity.     

Lewis acid-catalyzed atom transfer radical cyclization of unsaturated β-keto amides

The Lewis acid-catalyzed atom transfer radical cyclization reactions of olefinic -bromo β-keto amides were investigated. It was found Lewis acid Yb(OTf)₃ or Mg(ClO₄)₂ not only promoted the cyclization reactions, but also resulted in excellent trans stereocontrol in the cyclization products. With the catalysis of Lewis acid Yb(OTf)₃ or Mg(ClO₄)₂ at −78°C in the presence of Et₃B/O₂, the cyclization reactions of C-olefinic β-keto amides provided cyclic ketones, while the cyclization reactions of N-olefinic β-keto amides led to the formation of γ-lactams, which could be converted to 3-aza-bicyclo[3,1,0]hexan-2-ones.     

Proton-induced X-ray emission analysis of Jordanian cigarettes

Proton-induced X-ray emission spectroscopy was applied to determine the concentration of 11 elements in cigarette tobacco of four brands commercially made in Jordan, and one foreign brand. The results are expressed in absolute amount per cigarette. Cigarette wrapping paper and cigarette smoke were also analyzed. The significance of some of the elements found in the samples are discussed. Work carried out at the Department of Nuclear Physics, Lund Institute of Technology, Solvegatan 14, S-223 62, Lund, Sweden.