Allen method

For a recent approach that addresses some of the limitations of the Allen method, see P. Politzer, Z. P. Shields, F. A. Bulat, J. S. Murray, J. Chem. Theory Comput. 2011, 7, 377. 

Sha and colleagues synthesized several examples of the novel (isolable) 2,4-dihydropyrrolo[3,4- ]pyrrole ring system and found that the Diels-Alder reaction with DMAD occurred smoothly (Scheme 1, equation 1) [1]. Subsequent deamination using the Gribble and Allen method [2]... 

The Allen method introduced spectroscopic electronegativity as related to the average energy of the valence electrons in a free atom (Allen 1989),... 

Fig. 6.21 The construction of a system of periodic cells in the Ewald method. (Figure adapted from Allen M P and D ] Tildesley 1987. Computer Simulation of Liquids, Oxford, Oxford University Press.)...

Ojj 1.5068, was obtained in a yield of 82%. The equilibrium mixture obtained in the isomerization under the influence of KO-tert.-61,89 in DHSO consisted of about 70% of allene and 30% of yneamine. Base-catalysed isomerization is therefore not a suitable method to prepare the yneamCne. 

In the first method a secondary acetylenic bromide is warmed in THF with an equivalent amount of copper(I) cyanide. We found that a small amount of anhydrous lithium bromide is necessary to effect solubilization of the copper cyanide. Primary acetylenic bromides, RCECCH Br, under these conditions afford mainly the acetylenic nitriles, RCsCCHjCsN (see Chapter VIII). The aqueous procedure for the allenic nitriles is more attractive, in our opinion, because only a catalytic amount of copper cyanide is required the reaction of the acetylenic bromide with the KClV.CuCN complex is faster than the reaction with KCN. Excellent yields of allenic nitriles can be obtained if the potassium cyanide is added at a moderate rate during the reaction. Excess of KCN has to be avoided, as it causes resinifi-cation of the allenic nitrile. In the case of propargyl bromide 1,1-substitution may also occur, but the propargyl cyanide immediately isomerizes under the influence of the potassium cyanide. 

It was discovered in 1940 that some acetylenic chlorides are converted into allenes by treatment with a zinc-copper couple in ethanol. This method appears to... 

Over the past decade it has been established that for various substituents the i C chemical shift increment is a constitutive property. This applies to many systems e.g. benzenes, alkanes and alkenes. The availability of over 200 allenes, randomly substituted with groups of different nature, enabled us to prove that in the case of allenes the chemical shift increment is a constitutive property too, thus establishing a convenient method for estimating i ( C) values for allenes. 

We have exemplified the principal methods for allenes, cumulenes and also some new methods for acetylenic compounds by procedures for relatively simple structures. For each of the compounds the most suitable and economic method was selected. 

To integrate the Langevin equation, HyperChem uses the method of M.P. Allen and D.J. Tildesley, Computer Simulation of Liquids, Clarendon Press, Oxford, 1987 Ch.9, page 261 ... 

Kneaders Kneading Kneading mixers Knecht compound Knecht method Knife mills Knight and Allen Knives Knize Ten Knockdown Knockdown resistance... 

Knight and Allen. This is a copper reduction method for reducing sugars in white sugar up to 0.02%. It utilizes EDTA to determine excess unreacted copper. Tests undertaken in 1994 to extend the range of this method were unsuccesshil. In spite of poor performance in ring tests, it remains an official ICUMSA method. 

Heat Capacity. The multiple property estimation methods for constant pressure ideal-gas heat capacities cover a broad range of organic compounds (188,216,217). Joback s method (188) is the easiest to use however, usage of all these methods has been recommended only over the range 280—1100 K (7). An accurate method for ideal-gas heat capacities (constant pressure), limited to hydrocarbons, has been presented (218) that involves a fit of seven variables, and includes steric, ring, branching, alkene, and even allene corrections. 

A multiple-factor method for predesign cost estimating has been put forward by D. H. Allen and R. C. Paffe [Chem. Eng., 82, 142-150 (Mar. 3, 1975)] for fluid-type plants (F) that include some vapor processing. The method requires the following input information ... 

Different manufacturers have adopted different methods with minor changes to achieve almost the same objective. For example, field-oriented control was first introduced by Allen Bradley in the USA in 1981 and a similar technique was introduced at the same time by ABB of Finland. ABB claim their technique to be still faster in responding, as it eliminates the modulation section of... 

The acylation of Wittig reagents provides the most convenient means for the preparation of allenes substituted with various electron-withdrawing substituents. The preparation of o-allenic esters has been accomplished by the reaction of resonance-stabilized phosphoranes with isolable ketenes and ketene itself and with acid chlorides in the presence of a second equivalent of the phosphorane. The disadvantages of the first method are the necessity of preparing the ketene and the fact that the highly reactive mono-substituted ketenes evidently cannot be used. The second method fails when the a-carbon... 

Good reviews of the application of dynamic simulation methods to biomolecules can be found in the books by Brooks et al. [1] and McCammon and Harvey [2]. Good short reviews on this topic can also be found in Refs. 3-5. More detailed discussions of dynamic simulation methodologies can be found in books by Allen and Tildesley [6], Frenkel and Smit [7], and Rapaport [8] and in the review by van Gunsteren [9]. 

Numerous methods exist for determining erystal partiele eharaeteristies ineluding those listed in Table 1.3. See for example, Allen (1990) for a detailed survey and deseription of eaeh teehnique. Three eommonly used methods are illustrated below whilst mieroseopy is illustrated in Chapter 3 (Figure 3.11). 

One of the most dramatic developments in the chemistry of N2 during the past 30 years was the discovery by A. D. Allen and C. V. Senoff in 1965 that dinitrogen complexes such as [Ru(NH3)5(N2)1 could readily be prepared from aqueous RUCI3 using hydrazine hydrate in aqueous solution. Since that time virtually all transition metals have been found to give dinitrogen complexes and several hundred such compounds are now characterized.Three general preparative methods are available ... 

The polymerization filling was effected by the ion-coordination mechanism [17-19]. The monomers were ethylene, propylene, allene, os-butylene, butadiene. The fillers were mineral materials such as ash, graphite, silica gel, glass fibers. The ultimate aim of filler conditioning prior to polymerization is to secure, on its surface, metal complex or organometallic catalysts by either physical or chemical methods [17-19],... 

Polymerization thermodynamics has been reviewed by Allen and Patrick,323 lvin,JM [vin and Busfield,325 Sawada326 and Busfield/27 In most radical polymerizations, the propagation steps are facile (kp typically > 102 M 1 s l -Section 4.5.2) and highly exothermic. Heats of polymerization (A//,) for addition polymerizations may be measured by analyzing the equilibrium between monomer and polymer or from calorimetric data using standard thermochemical techniques. Data for polymerization of some common monomers are collected in Table 4.10. Entropy of polymerization ( SP) data are more scarce. The scatter in experimental numbers for AHp obtained by different methods appears quite large and direct comparisons are often complicated by effects of the physical state of the monomei-and polymers (i.e whether for solid, liquid or solution, degree of crystallinity of the polymer). 

In the 1980 s three monographs were published that cover parts of the present book, namely Quinone Diazides, by Ershov, Nikiforov, and de Jonge (1981), Aromatic Diazo Compounds, by Saunders and Allen (1985), and Williams Nitrosa-tion (1988). The book of Saunders and Allen which is actually the third edition of Saunders original book (1936, 1949), focuses on synthesis and preparative methods. The other two books emphasize rather the mechanistic and physical organic aspects of their subjects. 

An increased hydrogen ion concentration, that is a considerably greater amount of acid than the theoretical two equivalents of Scheme 2-1, is necessary in the diazotization of weakly basic amines. The classic example of this is the preparation of 4-nitrobenzenediazonium ions 4-nitroaniline is dissolved in hot 5-10 m HC1 to convert it into the anilinium ion and the solution is either cooled quickly or poured onto ice. In this way the anilinium chloride is precipitated before hydrolysis to the base can occur. On immediate addition of nitrite, smooth diazotization can be obtained. The diazonium salt solution formed should be practically clear and should not become cloudy on standing in the dark. Some practice is necessary, and details can be found in the books emphasizing preparative aspects (Fierz-David and Blangey, 1952 Saunders and Allen, 1985 in Houben-Weyl, Vol. E 16a, Part II, the chapter written by Engel, 1990). These books give a series of detailed prescriptions for specific examples and a useful review of the principal variations of the methods of diazotization. Such reviews have also been written by Putter (1965) and Schank (1975). 

Diaminobiphenyl (former name benzidine) can be easily bisdiazotized, but is not cleanly monodiazotized by reaction with one equivalent of a nitrosating agent. However, 4-aminobiphenyl-4,-diazonium ions are formed in a triazene equilibration of a 1 1 mixture of 4,4 -diaminobiphenyl with biphenyl-4,4 -bisdiazonium salts in aqueous HC1 (Tauber, 1894 see also Sec. 13.4). Methods for mono- and bisdiazotiza-tion of 1,4-diaminobenzene (/ -phenylenediamine) have been described by Saunders and Allen (1985, p. 29 see also Sec. 2.2). 

In most cases diazonium salts are not isolated, but are converted into products by reactions that can be carried out in situ. Moreover, it is actually recommended not to isolate these salts, not even for purification purposes, as many of them have a tendency to explode. In addition, the high solubility of most diazonium salts in water makes precipitation from this medium difficult. Therefore, to obtain solid diazonium salts the recommended method for many decades was to carry out diazotizations in ethanol followed by precipitation with ether. As inorganic salts of nitrous acid are scarely soluble in ethanol, Knoevenagel recommended alkyl nitrites (ethyl or isopentyl nitrite) as diazotization reagents as long ago as 1890. Various other solvents have subsequently been used for diazotizations with alkyl nitrites (see Saunders and Allen, 1985, p. 23 ff.), but as a method for obtaining solid diazonium salts this has been superseded by the isolation of diazonium tetrafluoroborates and, to a lesser degree, of hexafluorophosphates. 

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