Intermediate behavior

Between these two extremes of spontaneous rearrangement and total failure to rearrange, Braverman and Stabinsky36-38 have observed intermediate behavior. The reaction of crotyl alcohol with C13CSC1 afforded an equilibrium mixture of both crotyl trichlormethanesulfenate (13) and a-methylallyl trichloromethyl sulfoxide (14, equation 9). 

Some reactions of a given substrate under a given set of conditions display all the characteristics of Sn2 mechanisms other reactions seem to proceed by SnI mechanisms, but cases are found that cannot be characterized so easily. There seems to be something in between, a mechanistic borderline region. At least two broad theories have been devised to explain these phenomena. One theory holds that intermediate behavior is caused by a mechanism that is neither pure Sn I nor pure Sn2, but some in-between type. According to the second theory, there is no intermediate mechanism at all, and borderline behavior is caused by simultaneous operation, in the same flask, of both the SnI and Sn2 mechanisms that is, some molecules react by the SnI, while others react by the Sn2 mechanism. 

Though both miscible and immiscible blends are composite materials, their properties are very different. A miscible blend will exhibit a single glass transition temperature that is intermediate between those of the individual polymers. In addition, the physical properties of the blends will also exhibit this intermediate behavior. Immiscible blends, on the other hand, still contain discrete phases of both polymers. This means that they have two glass transition temperatures and that each represents one of the two components of the blend. (A caveat must be added here in that two materials that are immiscible with very small domain sizes will also show a single, intermediate value for Tg.) In addition, the physical properties... 

The same family of compounds shows another interesting feature, namely, the existence of borderline cases exhibiting an intermediate behavior between the concerted and stepwise mechanisms. More precisely, the width of the cyclic voltammetric peak and the variation of its location with scan rate change from a concerted to a stepwise behavior as the scan rate is raised (Fig. 4 and Scheme 6). 

The adsorbed species behaves like a gas in a polar medium or like a non polar solute in a polar solvent. This intermediate behavior between gas and liquid is well suggested by all the parameters studied. 

The Na salts in THF showed an intermediate behavior, and their spectra revealed an interesting temperature dependence. At + 25°C the spectra were very similar to those of the Li salts, but at - 52°C they had changed to the appearance of the spectra of the K salts. The spectra indicate a fast equilibrium 60 (X = Na) 61 with the latter favored by decreasing temperature. Analysis of the temperature dependence of individual chemical shifts allowed the evaluation of AH°, -6.9 kcal/mol, and AS0, -30 e.u., for this equilibrium (i.e., the contact-ion pairs are favored by entropy but disfavored by enthalpy). A similar effect may explain the temperature dependence of the NMR spectrum of 56. 

Elements from selenium through the middle rare earths will be present in the mixed fission product population they exhibit a wide variety of volatilities (1). The elements Y, Zr, and Nb and the rare earth oxides are high boiling and condensable at low partial pressures, whereas the noble gases, and the alkali metals Mo, Tc, Pd, Ag, Cd, Sn, Sb, Te, Ru, and perhaps Rh, are very volatile in a relative sense Sr and Ba are predicted to be of refractory or intermediate behavior. 

Many common reactions of aliphatic amines, ethers and sulfides (1) involve initial attack by an electrophilic reagent at a lone pair of electrons on the heteroatom salts, quaternary salts, coordination compounds, amine oxides, sulfoxides and sulfones are formed in this way. Corresponding reactions are very rare (c/. Section 3.3.1.3) with pyrroles, furans and thiophenes. These heterocycles react with electrophilic reagents at the carbon atoms (2-3) rather than at the heteroatom. Vinyl ethers and amines (4) show intermediate behavior reacting frequently at the (3-carbon but sometimes at the heteroatom. 

The yield of c-C3Fe was examined in detail at 22, 95, and 150°C by Cohen and Heicklen.40 Their data at 22 and 150°C are shown in Figures 2 and 3, respectively. The data at 95° followed an intermediate behavior. 

Competitive reactions with mixtures of the nucleotides GMP, CMP, AMP, and UMP provided information regarding the reactivities and selec-tivities of several transition metal moieties (335). Of the groups studied, the most extensive reaction occurred with tra 5-(NH3)2Pd(II), whereas the cis-Me2Au(III) moiety exhibited the lowest reactivity. MeHg(II) showed high selectivity for attack at N—H bonds, whereas the d.v-(NH3)2Pt(II) group showed a total preference for the purines, GMP and AMP. For the gold(III) and palladium(II) species intermediate behavior in terms of selectivity was observed. 

The two aluminum alkoxide primers on mild steel showed improved adhesion and better resistance to crack propagation with both the thermoplastic polyether-sulfone (PES) and the FM 300U thermoset epoxy adhesive. The titanium alkoxide exhibited the poorest resistance to crack growth, while tetrabutyl orthosilicate showed intermediate behavior between the two aluminum alkoxides and the titanium alkoxide. 

The problem of how to classify and account for this intermediate behavior continues to plague chemists interested in mechanism. The greatest difficulty arises for solvolysis, because the kinetic behavior with respect to solvent cannot be determined we shall be concerned here primarily with reactions of this type. 

Fig. 3.18. Exponential recovery (A) of Mz(t) of a nuclear spin / dipole coupled to a paramagnetic metal ion. When I is also coupled to another nuclear spin J, the latter also coupled to the metal ion, non-exponentiality occurs. If J relaxes slower than /, curves B and C are obtained for a selective and a non-selective experiment respectively. If J relaxes slower than /, curves D (selective) and E (non-selective) are obtained. If J relaxes at the same rate as /, a selective experiment gives an intermediate behavior between curves B and D (not shown), while a non-selective experiment gives pure exponential recovery (A). It is apparent that in all cases non-selective experiments perform better than selective experiments, as they are less sensitive to the non-exponentiality introduced by I-J coupling. Conditions R m = 10 s l R M = 20 s l (B,C), 5 s l (D,E) and 10 s l (A). The I-J cross-relaxation rate ou (Chapter 7) is —20 s"1.

With regard to miscible polymers, simple blending allows one to develop materials that frequently reveal an intermediate behavior between those of the individual blend components [2, 3], Such systems can be easily exploited for fine-tuning the foam-ability, for example by controlling important foaming parameters such as the melt rheology or the gas solubility. 

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