Group 9 reactivity studies

On the basis of evidence from reactivity studies, it has been suggested " that a variation of the SeI mechanism is possible in which the group Z becomes attached to X before the latter becomes detached ... 

Sjbberg B-M (1997) Ribonucleotide Reductases - A Group of Enzymes with Different Metallosites and a Similar Reaction Mechanism. 88 139-174 Slebodnick C, Hamstra BJ, Pecoraro VL (1997) Modeling the Biological Chemistry of Vanadium Structural and Reactivity Studies Elucidating Biological Function. 89 51-108 Smit HHA, see Thiel RC (1993) 81 1-40... 

Even in solution the relative rigidity of the polymer support can play a significant role in the reactivity of attached functional groups. Contrasting studies conducted with chloromethylated derivatives of poly(arylene ether sulfone) (Tg 175°C), phenoxy resin (Tg= 65°C) and polystyrene (Tg= 105°C) allow evaluation of chain rigidity effects. We have shown that the rates of quaternization of chloromethylated poly(arylene ether sulfones) and phenoxy resin deviate from the anticipated second order process at... 

In this paper, we describe the synthesis and initial reactivity studies of a macromolecule (Scheme 1) containing the isocyanide functional group [Z = -N=C ] tethered to a polysiloxane backbone. 

Intramolecular hydrogen bond is much stronger than the intermolecular hydrogen bond. The reactivity of such phenolic groups was studied by Pozdeeva et al. [51], Crown phenol A was synthesized, and the reactivity as chain terminating antioxidant in oxidized styrene (323 K) was studied. The chain terminating activity of this crown phenol A was compared with that of ionol. 

In general, wider polydispersity in functionality or group reactivity makes the gel time shorter and critical conversion lower. This conclusion is based on the results of theoretical and experimental studies concerning the effect of distributions in functionality and in group reactivity on crosslinking of functional stars [31-33],... 

The kinetic problem for the intramolecular cross-linking reactions in general form was not yet solved. Only some particular cases, i.e. the cvclization of macromolecules, the intramolecular catalysis and diffusion-controlled collision of two reactive groups were studied theoretically bv Xorawetz, Sisido and Fixman... 

In accord with the expected trans influence of the 71-acceptor aUenylidene unit [212], substitution of the chloride ligand by different anionic nucleophiles in complexes frans-[MCl(=C=C=CR R )(Pi-Pr3)2] (M = Rh, Ir) is favored, affording new aUenylidene derivatives frans-[MX(=C=C=CR R )(P/-Pr3)2] (X = I, F, OH, N3, etc.) (see reactivity studies below). Of particular interest is the behavior of the Rh(I) species frans-[RhCl(=C=C=CPh2)L2] (L = Pf-Pr3, f-Pr2AsCH2CH20Me) towards NaCsHs since the reactions lead to the clean formation of complexes 40 (Scheme 13), the only half-sandwich-type Group 9 allenylidenes presently known [206, 209]. 

As already commented in the introduction of this chapter, regardless of its substitution pattern, the main trends of allenylidene reactivity are governed by the electron deficient character of the C and Cy carbon atoms of the cumulenic chain, the Cp being a nucleophilic center [9-15]. Thus, as occurs with their allcarbon substituted counterparts, electrophilic additions on 7i-donor-substituted allenylidene complexes are expected to take place selectively at Cp, while nucleophiles can add to both C and Cy atoms. However, the extensive 71-conjugation present in these molecules results in a reduced reactivity of the cumulenic chain and, in some cases, in marked differences in the regioselectivity of the nucleophilic additions when compared to the all-carbon substituted allenylidenes. In the following subsections updated reactivity studies on 7i-donor-substituted allenylidene complexes are presented by Periodic Group. 

The rate constant for esterification is independent of x for the compounds studied (Table 2-2). Examples of similar behavior can be found for other reactions [Rand et al., 1965]. The results for sebacoyl chloride offer direct evidence of the concept of functional group reactivity being independent of molecular size, since the rate constant is independent of n as well as x. 

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