Kinetically stable

The last isomerization is remarkable in that the triple bond can shift through a long carbon chain to the terminus, where it is fixed as the (kinetically) stable acetylide. The reagent is a solution of potassium diami no-propyl amide in 1,3-di-aminopropane. In some cases alkali metal amides in liquid ammonia car also bring about "contra-thermodynamic" isomerizations the reactions are successful only if the triple bond is in the 2-position. 

At room temperature, pure N2H4 and its aqueous solutions are kinetically stable with respect to decomposition despite ihe endothermic nature of the compound and its positive free energy of formation ... 

Ta 1.5 X 10 2, K3 2.1 X 10 and 2.4 x and the corresponding negative logarithms are pA" 1.0, pA"2 1.8, pA"3 6.57 and pA"4 9.62. The P—O—P linkage is kinetically stable towards hydrolysis in dilute neutral solutions at room temperature and the reaction half-life can be of the order of years. Such hydrolytic breakdown of polyphosphate is of considerable importance in certain biological systems and has been much studied. Some factors which affect the rate of degradation of polyphosphates are shown in Table 12.10. 

Thirdly, strong solvent co-intercalation, in particular into internal van der Waals gaps, can only be expected for kinetically stable ternary compounds Li solv) Cn. For example, comparison of DMC and DEC with dimethoxyethane (DME), shows that the kinetic stability of Li>.(DME)yCn can be considered much higher than that of LiJr(DMC)vC and LiJt(DEC)yC and of course Liy(EC)yCn [169]. With EC/DME, solvent co-intercalation proceeds on a macroscopic scale, i.e., the external van der Waals gaps and some internal ones can participate in the solvent co-... 

Solvents which are kinetically stable with lithium show either high viscosity and high permittivity, or low viscosity and low permittivity. The diminution of high viscosity of solvents such as PC or EC is accom-... 

MeSSMe and inhibited to isomerise by a significantly larger isomerization barrier of 340 kj mol Thus, both H2S=S and Me2S=S are predicted to be kinetically stable toward unimolecular isomerization and should be experimentally observable in the gas phase or after matrix isolation. HF/b-SlG calculations indicate that the allyl analogue has a similar R2S=S/RSSR energy difference but a substantially lower activation barrier (110 kJ mol ) for rearrangement [25]. 

Antiaromatic molecules are kinetically unstable, and aromatic molecules are kinetically stable (Scheme 13). In cyclobutadiene, the n orbitals can be combined out of phase and the n orbitals can be combined in phase. Cyclobutadiene is kinetically unstable toward electron donors and acceptors. In benzene, all neighboring pairs of n orbitals cannot be combined out of phase, and all neighboring pairs of 71 orbitals cannot be combined in phase. Benzene is kinetically stable toward donors and acceptors. 

The kinetic stabilities and the donor-acceptor properties of cyclic conjugated molecules [68] have been described (Scheme 12) in the theoretical subsection (Sect. 2.2.2) to be controlled by the phase property. There is a parallelism between the thermodynamic and kinetic stabilities. An aromatic molecule, benzene, is kinetically stable, and an antiaromatic molecule, cyclobutadiene, is kinetically unstable (Scheme 13). 

Transition metal alkyls are often relatively unstable earlier views had attributed this either to an inherently weak M—C bond and/or to the ready homolysis of this bond to produce free radicals. Furthermore, the presence of stabilizing ir-acceptor ligands such as Cp , CO, or RjP was regarded as almost obligatory. However, (1) the M—C bond is not particularly weak compared say to the M—N bond, and (2) the presence of the new type of ligand on the metal could make the complex kinetically stable thus, even isoleptic complexes, i.e., compounds of the form MR , might be accessible 78, 239). These predictions have largely been borne out (see Table VII). 

A thermodynamically unstable structure can exist when its conversion to some other structure proceeds at a negligible rate. In this case we call the structure metastable, inert or kinetically stable. Since the rate constant k depends on the activation energy Ea and the temperature according to the Arrhenius equation,... 

The electrochemical intercalation/insertion is not a special property of graphite. It is apparent also with many other host/guest pairs, provided that the host lattice is a thermodynamically or kinetically stable system of interconnected vacant lattice sites for transport and location of guest species. Particularly useful are host lattices of inorganic oxides and sulphides with layer or chain-type structures. Figure 5.30 presents an example of the cathodic insertion of Li+ into the TiS2 host lattice, which is practically important in lithium batteries. 

In 1985/86 the first iminosilanes that are kinetically stable at room temperature were synthesized. Two groups demonstrated two different processes of preparation. 

The unsaturated silicon atoms form five bonds because of the donor. They have a tetrahedral environment and are four-coordinate. The adducts can be hydrolyzed very easily and are kinetically stable under normal conditions. One of the adducts, the THF adduct of Me2Si=N—Si(CMe3)3, has been isolated by Wiberg et al., as shown in Eq. (10).15... 

Structural analysis of the reaction products clearly shows that the ligand on silicon undergoes a haptotropic rearrangement from if -C5MC5 in 50 to in1 -C5MC5 in 52 and 53 as in the cases of oxygenation and thionation of 50.36 Apparently, silaneselone 51 is not kinetically stable enough to be isolated under normal conditions. 

Another way in which energy can be stored in aqueous solution is not only in organic compounds, as we shall see, but also in kinetically stable combinations of inorganic ions. An example is the molecule pyrophosphate, which stores energy at... 

---