Nonclassical molecules

The carbonium ion is a nonclassical molecule, because it contains a pentacoor-dinated carbon atom. It is very unstable and is therefore difficult to form. It is formed at temperatures of about 500°C. Once formed it readily decomposes to a carbenium ion by H2 formation or cracking (Fig. 4.70). 

Classical Configurations Associated with Nonclassical Molecules Three Car-boranes as Examples. 

Haselbach and Eberbach have reported an intriguing example of a reaction of the tricyclic system (70). " Photoelectron spectra as well as theoretical studies supported the intermediacy of the nonclassical molecule (71) in this reaction. 

The photochromism of bianthrone (72) is another example of a formal Gjv reaction. The structure of the colored form (73) has long been a subject of interest. The bond-twisted structure (73) was suggested after extensive NMR, UV-visible, and theoretical studies by Muszkat and his co-workers. Although the photochromism of bianthrone is formally similar to Gj photoreactions like the isomerization of trans-stilbene, the bond-twisted form in this case is a relatively stable nonclassical molecule. 

Dewar MJS, Nahlovskd Z, Ndhlovsky BD (1971) Diazabullvalene a Nonclassical Molecule Chem Commun 1971(21) 1377-1378... 

Nied D, Koeppe R, Klopper W, Schnoeckel H, Breher F (2010) Synthesis of a pentasila-propellane. Exploring the nature of a stretched silicon-silicon bond in a nonclassical molecule. J Am Chem Soc 132 10264... 

Early in the twentieth century physicists established that molecules are composed of positively charged nuclei and negatively charged electrons. Given their tiny size and nonclassical behavior, exemplified by the Heisenberg uncertainty principle, it is remarkable (at least to me) that Eq. (1) can be considered exact as a description of the electrostatic forces acting between the atomic nuclei and electrons making up molecules and molecular systems. Eor those readers who are skeptical, and perhaps you should be skeptical of such a claim, I recommend the very readable introduction to Jackson s electrodynamics book [1]. 

The elasticity can be related to very different contributions to the energy of the interface. It includes classical and nonclassical (exchange, correlation) electrostatic interactions in ion-electron systems, entropic effects, Lennard-Jones and van der Waals-type interactions between solvent molecules and electrode, etc. Therefore, use of the macroscopic term should not hide its relation to microscopic reality. On the other hand, microscopic behavior could be much richer than the predictions of such simplified electroelastic models. Some of these differences will be discussed below. 

The complex OsHCl(CO)(P Pr3)2 reacts with HX (X = H, SiEt3, Cl) molecules to give derivatives of the type OsXCl(r)2-H2)(CO)(P Pr3)2 (X = H, SiEt3, Cl), where the hydrogen atoms bonded to the osmium atom undergo nonclassical interaction (Scheme 16). 

The classical calorimetric methods addressed in chapters 7-9, 11, and 12 were designed to study thermally activated processes involving long-lived species. As discussed in chapter 10, some of those calorimeters were modified to allow the thermochemical study of radiation-activated reactions. However, these photocalorimeters are not suitable when reactants or products are shortlived molecules, such as most free radicals. To study the thermochemistry of those species, the technique of photoacoustic calorimetry was developed (see chapter 13). It may be labeled as a nonclassical calorimetric technique because it relies on concepts that do not fit into the classification schemes just outlined. 

In Equation 6.2 T(T) is equal to unity in classical TST, g(T) is a measure of the deviation from the assumption that reactant molecules are locally equilibrated, and k(T) describes the contribution from non-classical transmission through the barrier. k(T) is usually dominated by tunneling but also includes nonclassical reflections. 

Isotope (H (deuterium), discovered by Urey et al. (1932), is usually denoted by symbol D. The large relative mass difference between H and D induces significant fractionation ascribable to equilibrium, kinetic, and diffusional effects. The main difference in the calculation of equilibrium isotopic fractionation effects in hydrogen molecules with respect to oxygen arises from the fact that the rotational partition function of hydrogen is nonclassical. Rotational contributions to the isotopic fractionation do not cancel out at high T, as in the classical approximation, and must be accounted for in the estimates of the partition function ratio /. 

Jones et al. (1999) made a classification of the broad range of nucleation likely to be encoimtered in liquids supersaturated with dissolved gas molecules (Jones et al., 1999). Bubble formation from preexisting gas cavities larger than the critical size is referred to as nonclassical heterogeneous bubble nucleation (type TV bubble nucleation, following their... 

We have focused our attention on the prepolymer method for polyurethane development because we feel that it offers the researcher the greatest control of the molecule. We hope to encourage the scientific community to investigate other nonclassical polyurethane tools. If the pin posc of a device is purely physical, the large polyurethane manufacturers and chemists are the best resources for expertise. If, however, the intent is to experiment with a new polymerization technique for a particular medical or environmental application, the researcher must be able to assemble the component parts along lines with which the polyurethane industry may not be familiar. 

Nonclassic-.il complexes of dihydrogcn (page 645) may be thought of as complexes in an arrested transition state and iheire isiencc provides strong support fora concerted reaction mechanism. Dioxygen, another nonpolar molecule, also adds reversibly to Vaska s complex, bul in this case the X—Y bond is not completely broken. The bond order of 0 is reduced From two to essentially one. 

The nonclassical thiophenes (6), (12) and (13) show intense molecular ions (over 70%) as well as pronounced doubly charged M2+ ions. Other characteristic fragment ions result from the loss of phenyl or methyl substituents as the case may be. The thiobenzoyl fragment at m/e 121 (10-20%) is another common fragment in these molecules. The mass spectral fragmentation of tetraphenylthieno[3,4-c]thiophene (6) is presented in Scheme 6. 

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