Positions of addition

In calculations on proton addition complexes of azulene and methyl-azulenes by means of the HMO method, Heilbronner and Simonetta (1952) took the effect of methyl groups into aecount by adjustment of the a and j8 values, as had already been done by PuUmann and collaborators (1950) in calculating the spectra of the methylazulenes. These calculations correctly reproduce the effeet of a methyl group on the basicity of azulene. In contrast to the ease of naphthalene, the position of addition of the proton remains independent of the position of the methyl group ... 

There is reason to believe that the rate of addition of oxygen atoms to olefins and the position of addition (orientation) are not governed by the same factors. In the case of 2-pentene the addition takes place at the doubly bonded carbon atom to which the CH3 group is attached and not to the one where the C2HB group is attached. At the same time the rates of addition to propylene and to 1-butene are the same and in both cases terminal addition occurs. Similarly, the rates of addition to 2-butene and 2-pentene are also about the same. If the rates of addition and the orientation were determined by the same factors, approximately equal addition at the two double bond C-atoms would be expected. Since this is not the case, it appears reasonable to conclude that the transition state which determines the rates of addition occurs quite early in the reaction process, before oxygen atoms become localized on either of the two double bond C-atoms. 

Although an ET from phenolates is highly exothermic (for reduction potentials Lind et al. 1990 Jonsson et al. 1993) and ET is thermodynamically favored over addition (Lundqvist and Eriksson 2000), the usually preferred mode of reaction is addition rather than ET. Yet, addition and ET are in competition (Tripathi 1998), and, when the ortho- and the para-positions which are the relevant positions of addition for the electrophilic OH are blocked by a bulky substituent [e.g., reaction (34)] ET may become dominant (Table 3.3). Thus, also for these reactions a short-lived tx-complex [cf. reaction (6)] may be postulated as common precursor wherefrom the competition between addition and ET occurs. 

Alkyl radicals are nucleophilic radicals (cf. Walbiner et al. 1995 Wu and Fischer 1995 Wu et al. 1995 Heberger and Lopata 1998), and the preferred position of addition at a polarized C-C double bond is reversed compared to that of the electrophilic OH. Thus, in the case of Ura, the hydroxymethyl radical adds preferentially to the C(6)-position k 104dm3 mol1 s1 (Schuchmann et al. 1986 Chap. 10.5)]. 

Addition of sulphite occurs at an unsubstituted ring position. 6 Position of addition not determined. 

On the Equilibrium Position of Addition Reactions of Heteroatom Nucleophiles to Carbonyl Compounds... 

The equilibrium position of addition reactions to carbonyl compounds is also influenced by electronic substituent effects, as was also shown in Figure 9.1 ... 

Each azole ring can be ortho-fused to the azine ring in a characteristic and fixed number of ways the fused azole systems are subgrouped accordingly. Further organization is based on the relative position of the azine nitrogen and on the relative positions of additional heteroatoms in the azine ring. 

Figure 2. PXD data for a phase A preparation containing a significant phase B component. The sets of vertical bars indicate computed reflection positions based on a C-centered orthorhombic unit cell with a = 7.94A, b = 10.34A and c = 11.59A (phase A - lower), and a primitive cubic unit cell with a = 12.44A (phase B - upper). The positions of additional impurity peaks are indicated by e.

Aromatic acids of the form Ar—COOH are named as derivatives of benzoic acid, Ph—COOH. As with other aromatic compounds, the prefixes ortho-, meta-, and para-may be used to give the positions of additional substituents. Numbers are used if there are more than two substituents on the aromatic ring. Many aromatic acids have historical names that are unrelated to their structures. 

This work deals with the selective reduction of aromatic nitro compounds to the corresponding aromatic amines with hydrazine hydrate in the presence of catalytic amotmts of a modified iron oxide hydroxide compound. The dependence of the rate of reduction on the nature and the position of additional substituents other than the nitro group was determined. The rate is enhanced by elexAxan-withdrawing substituents and decreased by ectToordonating groups. 

Theoretical quantitative treatments of cycloadditions mainly concern the Diels-Alder reaction. A possible approach is that of calculating the para-localisation energy, that is the variation of Tr-electron energy of the conjugated diene system, when two Tr-electrons are localised upon the atoms, in 1,4-relation to each other, which must form the new tr-bonds. This has been done by Brown , using the molecular orbital method some successful predictions of reactivity and of the positions of addition for polycyclic aromatic hydrocarbons and polyenes were made. This method has also been used by other authors - . 

Nienow and Inoue (1993) gave an interesting set of examples using a small tank and the semibatch barium sulfate method of Villermaux to demonstrate the importance of feed position, as shown in Figure 13-8. In all cases the mixer speed and rate of addition were held constant only the position of addition was changed. All vessels were at about the same power per unit tank volume. The selectivity given is that of unwanted by-product. High numbers mean that more by-prodnct was formed. 

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