Contributing forms

Iminium ions (2) would be expected to undergo hydrolysis quite readily, since there is a contributing form with a positive charge on the carbon. Indeed, they react with water at room temperature." Acid-catalyzed hydrolysis of enamines (the last step of the Stork reaction, 12-18) involves conversion to iminium ions " ... 

We will assume that all the incident fields are polarized in the x-direction. The pump and Stokes focal fields, which each look like the complex fields depicted in Figure 9.1, set up an effective CARS excitation field E = (r) (r). The anti-Stokes polarization in the excitation volume induced by the effective excitation field can be considered as a collection of radiating dipoles. The resulting CARS amplitude at any far-field point Q with coordinates R = (R, 6, (j)) is a sum of the amplitude contributions form all these dipoles and is given by... 

A few words should be said about the difference between resonance and molecular vibrations. Although vibrations take place, they are oscillations about an equilibrium position determined by the structure of the resonance hybrid, and they should not be confused with the resonance among the contributing forms. The molecule does not resonate or vibrate" from one canonical structure to another. In this sense the term resonance is unfortunate because it has caused unnecessary confusion by invoking a picture of vibration. The term arises from a mathematical analogy between the molecule and the classical phenomenon of resonance between coupled pendulums, or other mechanical systems. 

Contributing forms must have the same number of unpaired electrons. For molecules of the type discussed previously, structures having unpaired electrons should not be considered since they usually involve loss of a bond... 

The free energy of activation of rotation in these ylides was calculated and was found to increase in the following order H > Ph > CN. Among these compounds, the cisoid structure (Z) was shown to be the major contributing form. 

Clearly, it is inconvenient and tedious to write the structures of the contributing forms to show the structure of a resonance hybrid. A shorthand notation is therefore desirable. Frequently, dashed rather than full lines are used where the bonding electrons are expected to be delocalized over several atoms. For benzene, 16a or 16b is quite appropriate ... 

A number of reactions are known in which a three-atom chain bearing four electrons in a n system adds to an olefin. These transformations, explored extensively by Huisgen and his collaborators,57 are known as 1,3-dipolar additions. The 1,3 dipoles are characterized by a structure for which at least one contributing form is of the dipolar type 24. Huisgen has identified two types of 1,3... 

The N — 3 primitive forms are linearly independent and independent of phase. A complete description of ring conformation is therefore possible in terms of normalized linear coefficients and the integers, k that identify the phases of the contributing forms as [Pg.222]

We hope that the contributions collected in this volume convey the stimulating and interdisciplinary atmosphere of the conference. We also expect that the results and discussions in these contributions form a first and decisive step toward understanding reaction processes from the standpoint of dynamics. 

In reaonatkce language, there are two contributing forms. Since tlof amide resonance stabilisation would be lost if the nitrogen atom urm pro tonated, pimtonation is disfavored. 

Comparing the UV spectrum of benzotriazole in different solvents with that of benzene and o-benzoquinone leads to the assumption that the principal contributing forms of the... 

A hybrid approach of the extended scaled particle theory (SPT) and the Poisson-Boltzmann (PB) equation for the solvation free energy of non-polar and polar solutes has been proposed by us. This new method is applied for the hydration free energy of the protein, avian pancreatic polypeptide (36 residues). The contributions form the cavity formation and the attractive interaction between the solute and the solvent to the solvation free energy compensate each other. The electrostatic conffibution is much larger than other terms in this hyelration free energy, because hydrophilic residues are ionized in water. This work is the first step toward further applications of our new method to free energy difference calculation appeared in the stability analysis of protein. 

Iminium ions (10) ° would be expected to undergo hydrolysis quite readily, since there is a contributing form with a positive charge on the carbon. Indeed,... 

In an equilibrium configuration, F is balanced by the nuclear contribution F, and the virial of the electronic contributions F, appearing in eqn (6.59) reduces to the nuclear-nuclear repulsive energy I in agreement with eqn (6.58) for the case where V, = 0. Thus, out of the total potential energy operator F, is purely electronic, as is purely nuclear, but contains contributions form both sets of particles. The electronic share of this potential energy of interaction is given by the projection of the virial operators for the electrons,... 

Structures I and II are reported as the main contributing forms. Meinwald (5) used these to explain the addition of ozone to certain olefins. A similar mechanism can be postulated to explain the reaction of ozone on tertiary amines ... 

These parameters have the same signs and their values are close. From these facts, we may take it that the ligand electrostatic contributions form a great part of the B4 (exp) and, moreover, that the rare-earth ion will not be very sensitive to the electrostatic field of the farthest ions. This screening phenomenon had been seen up to that time for the B2° parameter only. 

It has been predicted21-23 that tetra-substitution of cyclobutadiene with donor (D) and acceptor (A) groups, as in 11, will produce an optimal stabilizing effect, due to contributing forms 11c of tetramethylenecyclobutane structure. 

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