Delocalization, charge

Only noncondensed thiazoles in which mcsoionic charge delocalization involves atoms directly bonded to the thiazole ring are considered here. Two such svstems, 1 and 2. exist (Scheme 1). Structure 1 (X = Oi is... 

Resonance forms illustrating charge delocalization in enolate of a p keto ester... 

Kinetic data on acetate displacement from C-3 using a number of sulfur and nitrogen nucleophiles in aqueous solution at near neutral pH demonstrate that the reaction proceeds by an 5 1 mechanism (B-72MI51004). The intermediate in this reaction is depicted as a dipolar allylic carbonium ion (9) with significant charge delocalization. Of particular significance in this regard is the observation that the free carboxylate at C-4 is required since... 

Carbanion-stabilizing effects have been calculated at several levels of theory. Table 7.6 gives some gas-phase data. The AMI and PM3 semiempirical calculations have also been done in water. The order NO2 > CH=0 > CN > Ph > CH2=CH is in accord with the experimental trends and reflects charge delocalization. The electronegative substituents F, OH, and NH2 are stabilizing by virtue of polar effects. The small stabilization provided by CH3 is presumabfy a polarization effect. 

Aryl acylium ions have substantial charge delocalization into the aromatic ring. 

Compare electrostatic potential maps for planar and pyramidal forms of 2-methyl-2-propyl anion. For which is the negative charge more delocalized Is this the lower-energy structure For this case, does charge delocalization lead to stabilization Explain. 

Obtain energies for each ion and for their correspondin precursors benzoic acid,phenol and cyclohexanol). Us this information to calculate the energy for each of the abov deprotonation reactions. (The energy of proton is given left.) Is the trend consistent with the experimental pKa dat (see table at left) Does deprotonation energy parade charge delocalization in these systems Explain ho electron delocalization affects the reactivity of these acidf... 

Both protonated forms place the formal positive charge on one of the nitrogens. Is charge delocalization more effective for one of the structures over the other, making it the more stable ... 

What other factors might be responsible for difference in activation energies Compare atomic charges anc electrostatic potential maps for the Sn2 transition states Does the increase in steric crowding lead to enhanced o diminished charge delocalization Explain. How, if at all would this be expected to affect the energy barrier Why ... 

Phenol has different chemical properties from those of typical alcohols. Display the electrostatic potential map for phenol. Does this suggest that phenol is likely to be a stronger or weaker acid than any of the compounds discussed above Compare the electrostatic potential map for 4-nitrophenol to that for phenol. What effect does substitution by nitro have on acid strength Explain your result by considering charge delocalization in the conjugate base. Draw all reasonable Lewis structures for phenoxide anion and for 4-nitrophenoxide anion. Which is more delocalized Is this consistent with experimental pKa s ... 

According to Branchini et al. (2004), luciferase modulates the emission color by controlling the resonance-based charge delocalization of the anionic keto-form of oxyluciferin in the excited state. They proposed the structure C5 as the yellow-green light emitter, and the structure C6 as the red light emitter. 

Noncoordination anions with extensive charge delocalization have been very suc-cesful in enhancing the performance of dry polymer electrolytes. Examples of these are given in Table 1. 

The evaluation of polarographic redox potentials of anthracene- and phenanthrenediazonium ions indicates, however, that the charge delocalization into these aromatic rings may be smaller (Elofson et al., 1984 b). 

The origin of the dependencies of AAg on rion can be rationalized in the following way. When the smaller metals are bound to the enzyme, the free energy of ij/2 will be lowered considerably more than that of the transition state (as well as i//3) since in the former the OH " ion is free to interact with or ligate the metal, while it is becoming partially bound to the 5 -P atom at the transition state with accompanying charge delocalization. On the other... 

Structures with a cyclic character (70° a 110°) are less solvated than open cation structures (a < 70° a > 110°) due to a larger charge delocalization in the former. Thus, the alterations of the potential energy surface described above are plausible. There are two possible structures for activated complexes in solution. They... 

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