Nucleophilic attack physical properties

Reactions of the Disulfide Group. Besides the thiol end groups, the disulfide bonds also have a marked influence on both the chemical and physical properties of the polysulftde polymers. One of the key reactions of disulfides is nucleophilic attack on sulfur (eq. 4). The order of reactivity for various thiophiles has been reported as (C2H O) P > R, HS , C2H5 S- >C,H,S- >C,H,P,... 

A comparison of steric influence resulting from more than 80 different silyl groups is summarized in Table 1. The trend is established on the basis of reaction yields, rates and selectivity, as well as on reactivity and physical properties of organosilanes. Two different effects may be involved (a) the effect of a silyl group on reactions taking place at the neighboring centers, and (b) the effect of the groups attached to silicon on the nucleophilic attack at the silicon atom. 

The particular feature that defines the class, and contributes to useful characteristics and to limitations is the N - S bonds, a linkage which within the constraints of the generic formula is particularly susceptible to nucleophilic attack. This requires that useful members of the class possess low solubility, particularly aqueous, so that hydrolytic destruction may be maintained at a low practical limit. We have correlated field usefulness of members of this class to their chemical and physical properties as above discussed. 

In addition to possessing physical properties compatible with car-bene character at C , alkenyl ketone rings with a hydrogen on C are susceptible to nucleophilic attack by PMe3 [Eq. (61)]. A full paper de-scribing several 1 1 adducts and including the structure of Cp(CO)2-... 

Os(NH3)5(N2)]l2 is air-stable and inert to replacement of N2, except on oxidation. It can be diazotized with HNO2, giving [Os(NH3)4(N2)2]. Other chemical and physical properties have been reported. > > The salt [Os(NH3)e]-I3 appears to be similar to its ruthenium analog but has been investigated only briefly.2,5 [Os(NH3)s(NO)]3+ is reversibly deprotonated to form [Os(NH2)-(NH3)4(NO)]2+, and may be reduced with zinc to [Os(NH3)e] or with hydrazine to [Os(NH3)s(N2)] +. None of the nitrosyls synthesized here is susceptible to nucleophilic attack at the NO+ group. All are diamagnetic, and their other... 

Physical properties indicate that the dipolar contribution (1) is the major one and this structure actually accounts for the nucleophilic behavior of the terminal carbon of isonitriles. However, in terms of radical chemistry, the more interesting form is the divalent one (2). This clearly shows that the isonitrile group does not behave toward radical species like a vicinal radical acceptor/radical donor synthon, that is, like an usual unsaturated bond. It instead reacts like a geminal acceptor/donor synthon [2], where an incoming radical attacks the same carbon atom that will be the new radical center in the resulting imidoyl intermediate 3 (Scheme 1). Actually, isonitriles can serve as very efficient radical traps and this chapter reviews the structural, mechanistic, and synthetic studies carried out in this field, with outstanding results, in the last three decades. 

The use of a mixed-valent, dinuclear iron site, similar to those in hemerythrin and ribonucleotide reductase,to catalyze a nonredox reaction such as phosphate ester hydrolysis is novel and unexpected for a variant of the familiar oxo(hydroxo)-bridged diiron center. In contrast to the general agreement that exists regarding the spectroscopic and physical properties of the PAPs, their kinetics properties and especially their mechanism of action remain controversial. Much of the disagreement stems from the different pH dependences of the catalytic activity of BSPAP and Uf, which is due to the fact that the former is isolated in a proteolytically activated form while the latter is not. Proteolysis results in a substantial increase in optimal pH in addition to an increase in catalytic activity at the optimal pH. "" Current data suggest that many of the spectroscopic studies described in the literature were performed on a catalytically inactive form of the enzyme. As a result, the roles of the trivalent and divalent metal ions in catalysis and in particular the identity of the nucleophilic hydroxide that directly attacks the phosphate ester remain unresolved. 

Heteroatoms in five-membered 7i-excessive heteroaromatic compounds are responsible for the chemical behaviour of the molecules as a whole. The heteroatoms not only give electrons to form an aromatic n-electron system but also determine the direction of the attack of electrophilic or nucleophilic agents. In fused 7i-excessive heterocycles containing two or more heteroatoms, the reactivity of compounds and their physical properties are substantially affected by both the mutual arrangement of the heteroatoms and the electronic effects associated with their nature. 

The physical and spectral properties of 1,3-thiazole are similar to those of pyridine in some ways. The electronegative A -atom at the 3-position makes C(2) partially electropositive and consequently susceptible to nucleophilic attack. 

The dication Fv[Rh2(CO)4] 2+, 12 +, is quite sensitive to nucleophilic attack. Care must be exercised in order to obtain its physical properties. Spectroelectrochemical experiments at 243 K in CH2CI2 gave the vibrational spectrum, AvQQ(syTSi) = 113 cm , AvQo(asym) =141 cm" followed by decomposition of the dication.[17]... 

Another research group published numerous studies of syntheses and physical properties of LC-polyethers having linear chains, hyperbranched and cyclic structures or containing discotic mesogens [327-341]. All these different LC-polyethers were prepared via the normal Williamson ether synthesis involving the nucleophilic attack of a phenoxide ion onto a bromoalkane. For instance, numerous linear LC-polyesters were prepared from the mesogenic diphenols outlined in (214) and formulas (215a,b) [327,337]. 

Since heteroaromatic compounds sometimes exhibit interesting physical properties and biological activities, construction of substituted heteroaromatics has drawn some attention. Heteroaromatics can be divided into two major categories. One is the tt-electron-sufhcient heteroaromatics, such as pyrrole, indole, furan, and thiophene those easily react with electrophiles. The other is the 7r-electron-deficient heteroaromatics, such as pyridine, quinoline, and isoquinoline those have the tendency to accept the nucleophilic attack on the aromatic ring. Reflecting the electronic nature of heteroaromatics, the TT-electron-deflcient ones are usually used as the electrophiles.t The rr-electron-sufficient heteroaromatics having simple structures, such as 2-iodofuran and 2-iodothio-phene, have also been utilized as the electrophiles. Not only the electronic nature of the heteroaromatics but also coordination of the heteroatom to the palladium complexes influence catalytic activity. This is another reason why the couphng reaction did not proceed efficiently in some cases. 

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