Corresponding transition

STO-3G calculations find the corresponding transition state to be more stable than other possible conformations by several kilocalories per raole. The origin of the preference for this transition-state conformation is believed to be a stabilization of the C=0 LUMO by the a orbital of the perpendicularly oriented substituent. 

Alkali-metal graphites are extremely reactive in air and may explode with water. In general, reactivity decreases with ease of ionization of M in the sequence Li > Na > K > Rb > Cs. Under controlled conditions H2O or ROH produce only H2, MOH and graphite, unlike the alkali-metal carbides M2C2 (p. 297) which produce hydrocarbons such as acetylene. In an important new reaction CgK has been found to react smoothly with transition metal salts in tetrahydrofuran at room temperature to give the corresponding transition metal lamellar compounds ... 

Owing to the two different kinds of stereoselectivity, four products are possible for this reaction. However, calculations of the corresponding transition states show that 45a is the kinetically favored species. 

Electron Correlation The theory should have a limiting case of exact total energies, electron binding energies and corresponding transition probabilities. 

The following chapter concerns another kind of low-valent organophosphorus compounds, namely phosphinidenes. Little is known about free phos-phinidenes in contrast to the corresponding transition metal complexes. Many new reagents have been generated exhibiting either electrophilic or nucleophilic properties. The reactivity of these carbene-like reagents is evaluated (K. hammer tsma). 

A lifetimes comparison for each excited state (Table 8) shows that they are smaller for the A n state except for v =0. The vibrational decays occur by means of cascade processes. Rotational effects (v =l - 2 i =l - 2) appear to be even more intense than for the corresponding transition bands and in either case these effects disappear for j =4. For... 

The concentrations of the reactants and reaction prodncts are determined in general by the solution of the transport diffusion-migration equations. If the ionic distribution is not disturbed by the electrochemical reaction, the problem simplifies and the concentrations can be found through equilibrium statistical mechanics. The main task of the microscopic theory of electrochemical reactions is the description of the mechanism of the elementary reaction act and calculation of the corresponding transition probabilities. 

The seven-compartment transit model may be physiologically sound. We may visualize that the first half of the first compartment represents the duodenum the second half of the first compartment, along with the second and third compartments, the jejunum and the rest of the compartments the ileum. The corresponding transit times in the duodenum, jejunum, and ileum are 14, 71, and 114 min, respectively. Considering the volumes and flow rates in these three segments [71,72], such an assignment seems reasonable. 

Increasing the number of acid sites, the C-methylation becomes largely preferred over the O-methylation (the QC-mcthylation ratio increased), while between the two ortho-C-methylated compounds, 2,5-DMP becomes more preferred than 2,3-DMP, in agreement with the calculated energies for the corresponding transition states. Disagreement between results obtained in gas-and liquid-phase methylation with the Mg/Fe/O catalyst (Table 2) concerns the ortho/para-C-methylation ratio (which in liquid phase was not varied when the Fe content was increased), and the 2,5-DMP/2,3-DMP ratio (which in gas phase... 

In order to determine the structural factors maximizing 2PA cross section values, we analyze (8) from Sect. 1.2.1. For all cyanine-like molecules, symmetrical and asymmetrical, several distinct 2PA bands can be measured. First, the less intensive 2PA band is always connected with two-photon excitation into the main absorption band. The character of this 2PA band involves at least two dipole moments, /

symmetry forbidden for centro-symmetrical molecules, such as squaraines with C, symmetry due to A/t = 0, and only slightly allowed for polymethine dyes with C2V symmetry (A/t is small and oriented nearly perpendicular to /t01). It is important to note that a change in the permanent dipole moment under two-photon excitation into the linear absorption peak, even for asymmetrical D-a-A molecules, typically does not lead to the appearance of a 2PA band. 2PA bands under the main absorption peak are typically observed only for strongly asymmetrical molecules, for example, Styryl 1 [83], whose S0 —> Si transitions are considerably different from the corresponding transitions in symmetrical dyes and represent much broader, less intense, and blue-shifted bands. Thus, for typical cyanine-like molecules, both symmetrical and asymmetrical, with strong and relatively narrow, S (I > S) transitions, we observe... 

Nonradiative transfer of excitation energy requires some interaction between donor and acceptor molecules and occurs if the emission spectrum of the donor overlaps the absorption spectrum of the acceptor, so that several vibronic transitions in the donor must have practically the same energy as the corresponding transitions in the acceptor. Such transitions are coupled, i.e., they are in resonance, and that is why the term resonance energy transfer (RET) or electronic energy transfer (EET) are often used. 

Oie, T., I. A. Topol, and S. K. Burt. 1995. Ab initio and Density Functional Studies on Internal-Rotation and Corresponding Transition-States in Conjugated Molecules. J. Phys. Chem. 99, 905. 

The END equations are integrated to yield the time evolution of the wave function parameters for reactive processes from an initial state of the system. The solution is propagated until such a time that the system has clearly reached the final products. Then, the evolved state vector may be projected against a number of different possible final product states to yield corresponding transition probability amplitudes. Details of the END dynamics can be depicted and cross-section cross-sections and rate coefficients calculated. 

As a result of the inductive and hyperconjugative effects it is to be expected that tertiary carbonium ions will be more stable than secondary carbonium ions, which in turn will be more stable than primary ions. The stabilization of the corresponding transition states for ionization should be in the same order, since the transition state will somewhat resemble the ion. Thus the first order rate constant for the solvolysis of tert-buty bromide in alkaline 80% aqueous ethanol at 55° is about 4000 times that of isopropyl bromide, while for ethyl and methyl bromides the first order contribution to the hydrolysis rate is imperceptible against the contribution from the bimolecular hydrolysis.217 Formic acid is such a good ionizing solvent that even primary alkyl bromides hydrolyze at a rate nearly independent of water concentration. The relative rates at 100° are tertiary butyl, 108 isopropyl, 44.7 ethyl, 1.71 and methyl, 1.00.218>212 One a-phenyl substituent is about as effective in accelerating the ionization as two a-alkyl groups.212 Thus the reactions of benzyl compounds, like those of secondary alkyl compounds, are of borderline mechanism, while benzhydryl compounds react by the unimolecular ionization mechanism. 

For many years, investigations on the electronic structure of organic radical cations in general, and of polyenes in particular, were dominated by PE spectroscopy which represented by far the most copious source of data on this subject. Consequently, attention was focussed mainly on those excited states of radical ions which can be formed by direct photoionization. However, promotion of electrons into virtual MOs of radical cations is also possible, but as the corresponding excited states cannot be attained by a one-photon process from the neutral molecule they do not manifest themselves in PE spectra. On the other hand, they can be reached by electronic excitation of the radical cations, provided that the corresponding transitions are allowed by electric-dipole selection rules. As will be shown in Section III.C, the description of such states requires an extension of the simple models used in Section n, but before going into this, we would like to discuss them in a qualitative way and give a brief account of experimental techniques used to study them. 

The 10-fold disadvantage of the latter 1,2-H migration can be attributed to destabilization of the corresponding transition state by the inductively electron-withdrawing CF3 bystander.14... 



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