Lewis representative procedure

Representative Procedure for Bronsted Add Promoted Glycosylation with Cl-Hemiacetal Donors Using Methoxyacetic Add 128 Representative Procedure for Lewis Acid Promoted Glycosylation with Cl-Hemiacetal Donors Using Sn(OTf)2 and LiC104 129... 

Representative Procedure for Lewis Acid Promoted Clycosylation with Glycosyl Acetate Donors Using SnCI4 [198]... 

For the Lewis base (LB) study, the following reaction conditions were held constant temperature= -lO C, reaction volume= 0.2L, [IB]o= 2M, [TMPCl]o= 0.06M, [BCl3]= 0.06M. A representative procedure was as follows an air background spectrum was acquired by fitting a stainless steal sleeve to the end of the DiComp probe of the ReactIR 1000 and immersing... 

The general procedure for constructing Lewis-like diagrams for transition-metal species can best be illustrated by representative examples. From Table 4.1 one can recognize that the first transition series (Sc-Zn) includes a disproportionate number of exceptional cases compared with later series, and illustrative examples will therefore be drawn primarily from the third transition series (La-Hg). (The somewhat anomalous behavior of the first transition series and general vertical trends in the d-block elements will be discussed in Section 4.10.)... 

The BLW method can be considered as an extension of the orbital deletion procedure (ODP) (51,52), a simpler method that can only be applied to carbocations (52) and boranes (51). The ODP consists of representing a resonance structure displaying an electronic vacancy (Lewis acid character) by deleting the primitive basis functions corresponding to the empty site before launching the SCF calculation. As a typical example, the ODP has been applied to calculate the resonance energy of the allyl cation (52). 

It therefore seems quite natural to choose silica, silica aluminas, and aluminium oxide as the objects of the first systematical quantum-chemical calculations. These compounds do not contain transition elements. They are built of the individual structural fragments primary, secondary, etc. This enables one to find the most suitable cluster models for quantum-chemical computations. The covalent nature of these structures again makes quite efficient a comparatively simple method of taking into account the boundary conditions in the cluster calculations. Finally, these systems demonstrate clearly defined Bronsted and Lewis acidity. This range of questions comprises the subject of the present review. This does not by any means imply that there are no quantum-chemical computations on the cluster models of the surface active sites of transition element oxides. It would be more proper to say that the few works of this type represent rather preliminary attempts, being far from systematic studies. Also, many of them unfortunately include some disputable points both in the statement of the problem and in the procedure of calculations. In our opinion, the situation is such that it is still unreasonable to try to summarize the results obtained, and therefore this matter is not reviewed in the present article. 

The classic papers by Lewis and Matheson [Ind. Eng. Chem., 24, 496 (1932)] and Thiele and Geddes [Ind. Eng. Chem., 25, 290 (1933)] represent the first attempts at solving the MESH equations for multicomponent systems numerically (the graphical methods for binary systems discussed earlier had already been developed by Pon-chon, by Savarit, and by McCabe and Thiele). At that time the computer had yet to be invented, and since modeling a column could require hundreds, possibly thousands, of equations, it was necessary to divide the MESH equations into smaller subsets if hand calculations were to be feasible. Despite their essential simplicity and appeal, stage-to-stage calculation procedures are not used now as often as they used to be. 

The SNl-type transformation of secondary and tertiary alkanols with the help of trichloroacetic acid and hydrazoic acid has also been mentioned in Section I.8.4.2.I. Several azides, e.g. of the adamantane and diamantane series, have been obtained on treatment of the corresponding alcohols with NaNs and sulfuric acid. As expected, this procedure lends itself particularly well to the formation of tertiary azides." Treatment of tertiary carbinols with HN3 and BF3 or other Lewis acids represents another route... 

In conclusion, the Boys localization procedure may be considered as the mathematification of the qualitative Lewis and Linnett theories. As pointed out, in this perspective a formal signification of the symbols used by these authors can be proposed these represent not localized electrons but centroids of charge of localized orbitals. Within this interpretation, the former theories agree much better with the ideas of quantum mechanics such as the wave character of electrons that prevents their localization. Moreover, the results obtained by the Boys procedure allow us to predict the Lewis and (or) Linnett structures of many chemical species without performing explicit calculations. For example, linear and bent 1,3-dipoles are described by the following general formulas ... 

A wide variety of numerical methods have been proposed for solving the set of equations represented by Eq. (2-1). Two fundamentally different iterative procedures have been proposed for solving these equations namely the Lewis and Matheson method10 and the Thiele and Geddes method.14 In the Lewis and Matheson method, the terminal compositions Xm and xBi are taken to be the independent variables, and in the Thiele and Geddes method, the temperatures (the temperature of each stage) are taken to be the independent variables. Up until about 1963, the Lewis and Matheson choice of independent variables was used almost exclusively, and since then, the Thiele and Geddes choice of the independent variables has become the most popular. 

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