Perfect caging

For about twenty seconds she stood absolutely still, face a perfect cage around any emotion. Then her finger lined up on a spindly youth in a baggy white suit. "You, open the muscle membrane we ll use the stairs."... 

Singlet-state ntt reactions that occur in the gas phase and in solution may not be observed in crystals because the acyl-alkyl radical pair (E) is subject to the perfect cage effect . Radical-radical recombination in the singlet-state acyl-alkyl biradical (from E =>A) may occur within the time scale of a single bond vibration. However, because many decarbonylation reactions have been documented in crystals, conditions may be satisfied for a-cleavage to compete with excited-state decay and for decarbonylation to compete with recombination of the acyl-alkyl radical pair. In this chapter, we review various aspects of the a-cleavage and decarbonylation steps in the reaction, describe recent theoretical advances, and conclude with examples that reflect our current understanding of the reaction in the solid state. 

The function 0(7) is again defined by Eq. 10 and represents the contributions due to translational motion and internal degrees of freedom of the solute molecule.t The second term is related to the potential energy w o) of the solute molecule at the center of its cage referred to the perfect gas, and the integral is the Tree volume of the solute molecule wandering in the cavity. In order to conform with the customary notation of the L-J-D theory we shall further write the free volume as... 

To reach W = 1 and S = 0, we must remove as much of this vibrational motion as possible. Recall that temperature is a measure of the amount of thermal energy in a sample, which for a solid is the energy of the atoms or molecules vibrating in their cages. Thermal energy reaches a minimum when T = 0 K. At this temperature, there is only one way to describe the system, so — 1 and — 0. This is formulated as the third law of thermodynamics, which states that a pure, perfect crystal at 0 K has zero entropy. We can state the third law as an equation, Equation perfect crystal T=0 K) 0... 

There is no perfect system for identification of animals. Tattoos and color codes frequently fade and may need to be redone after 3 to 5 months. Toe clips and ear punches are occasionally obliterated by self-mutilation or mutilation by cage mates. Ear tags and collars fall off and need to be replaced. Cage cards can be lost or destroyed. Whatever system or combination of systems of animal identification are selected by a laboratory, the shortcomings of the selected sys-tem(s) must be recognized, and procedures must be developed to address those shortcomings. 

The chemistry of all fullerenes is dominated by their ability to react as poorly conjugated and electron-deficient 2ir alkenes they show very few properties typical of dienes or arenes (5). In addition, because of the high cage stability, they never undergo substitutions. C60 shows behavior similar to that of a monosubstituted alkene such as vinyl chloride or acrylate. All fullerenes readily add to electron-rich species such as nucleophiles, bases, radicals, or reducing agents. They are, for example, perfect dienophiles for Dieles-Alder reactions. The types of reactions undergone by fullerenes are illustrated in Scheme 1. 

On the other hand, the electron-accepting features of the fullerene, as incorporated into the triads, are perfectly preserved. All oligomers exhibit a localization of the LUMO exclusively surrounding the symmetrical CV,o cage. Furthermore, the short distance between donor and acceptor in the monomer 15a leads to significant overlap between HOMO and LUMO, giving rise to extremely fast electron-transfer processes. 

The probable existence of an interstitial H atom in a molecular (i.e., non-poly-meric) complex was first suggested in a paper by Eady, Johnson, Lewis and coworkers on [HRu6(CO)18] 249). In the X-ray study of this anion, the H atom was not directly located, but was presumed to be in the center of the metal cage on the basis of the near-perfect octahedral symmetry of the cluster. There were no discernible distortions of the cluster or its ligands which might have indicated an alternative placement of the H atom. 

Salts of the bases MOH are crystalline, ionic solids, colorless except where the anion is colored. For the alkali metal ions the energies required to excite electrons to the lowest available empty orbitals could be supplied only by quanta far out in the vacuum ultraviolet (the transition 5p6 —5p56s in Cs+ occurs at 1000 A). However, colored crystals of compounds such as NaCl are sometimes encountered. Color arises from the presence in the lattice of holes and free electrons, called color centers, and such chromophoric disturbances can be produced by irradiation of the crystals with X rays and nuclear radiation. The color results from transitions of the electrons between energy levels in the holes in which they are trapped. These electrons behave in principle similarly to those in solvent cages in the liquid ammonia solutions, but the energy levels are differently spaced and consequently the colors are different and variable. Small excesses of metal atoms produce similar effects, since these atoms form M+ ions and electrons that occupy holes where anions would be in a perfect crystal. 

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