Energy deprotonation

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... 

Is the most delocalized enolate also the most easily formed enolate Calculate relative deprotonation energies from the enolate precursors using the deprotonation energy of acetone as a standard. 

Table 2-2. 1-, 2- and 3-layered ONIOM calculations for the deprotonation energy (in kcal/mol) of NH —CnBuH — CO—NH—CH2 — CO—NH — CHnBu — COO- system using the optimized geometries by the respective methods (Reprinted with permission from Morokuma et al. [11]. Copyright 2006 American Chemical Society.)... 

To summarize, we have systematically tested all possible three- and two-layer ONIOM combinations of high-level QM (HQ=B3LYP/6-31G ), low-level QM (LQ=AM1), and MM (Amber) for the deprotonation energy and structure of a test molecule, an ionic form of a peptide. We find the errors introduced in the ONIOM approximation, in comparison with the target HQ (or HQ HQ HQ) calculation, generally increases in the order ... 

There is no well-defined way of calculating deprotonation energy with Amber. However, this does not matter as it totally cancels out in ONIOM by taking the difference between the real and model system. 

The calculated deprotonation energies of ethane, ethylene and acetylene by SCF Hartree-Fock (FIF) and MP2 methods follow the expected order 456, 455 (basis... 

TABLE 4. SCF and MP2 energies for ethylene and vinyl anion and the deprotonation energy (A/7lcid) for ethylene0,6... 

All of the azoles showed a linear variation of these values except the pyrazoles, which belong to a parallel line 4.5 pK units apart. Fully optimized INDO geometries have been calculated for 12 azoles, as well as their cations and anions, both isolated and specifically solvated by five water molecules166. Evaluation of the protonation and deprotonation energies of the solvated molecules indicates a behaviour similar to that found experimentally in solution. In particular, the difference between pyrazoles (and indazoles) and all the other azoles is a consequence of the protonation of the nitrogen contiguous to NH, that is due to a difference in basicity. 

Among the semiempirical methods used to evaluate protonation and deprotonation energies in azoles, only INDO seems to estimate the electrostatic proximity effects167 correctly. 

While average deprotonation energy is a good measure of the intrinsic Bronsted acid strength of a zeoHte, it is the extrinsic acidity, also impacted by the chemical interaction between the protonated basic probe molecule and the deprotonated zeoHte, that really counts for catalysis. 

Deprotonation energies for 9-substituted fluorenes, calculated using AMI semiem-pirical MO theory, correlate linearly with acidities determined experimentally for these heteroatom-substituted compounds. ... 

Computational estimates of the gas-phase deprotonation energies of tetraphos-phacubane (16a) and its tetraoxide (16b) and tetrasulfide (16c) at MP2/6-31 +... 

Note This change in the Ng-Hg bond is smaller than that of the elongation of the Ng-Hg bond in the complex A-Au3(N3) discussed in Subsection 5.3. Therefore by the absolute value, the red shift of z/(Ng-Hg) is also larger than that of z (Ng-Hg). To explain this difference, let us recall that the deprotonation energy (enthaply) DPE(Ng-Hg) = 336.8 kcal/mol < DPE(Ng-Hg) = 355.2 kcal/mol (see, e. g.. Ref. [41] and references therein), and therefore, the Ng-Hg bond is stronger perturbed by Aug than Ng-Hg ... 

The choice of cluster model size is critical. It is essential that the cluster model be neutral and not subjected to optimization constraints. Both these restrictions have been shown to lead to artifactual behavior. Small clusters cannot be used to investigate concentration dependence, and if this dependence is to be considered, a larger model must be used. Similarly, a cluster should not be so small that it artificially constrains the spatial extent of the adsorbate complex or transition state. The acidity of the cluster—quantified by the deprotonation energy—is found to change as a function of cluster size. The deprotonation energy of a 3T atom cluster terminated with hydro-... 

The parent acids and alcohols, on the other hand, are not expected to display any significant mesomeric stabilisation, because this would involve the participation of some rather unreasonable Lewis structures with separated positive and negative charges. As a consequence, the tt-delocalisation in 1 and 2 is a factor that lowers the deprotonation energy of carboxylic acids and enols, thus reinforcing their acidity, according to standard organic-chemistry textbooks. 

An important factor that controls the Bronsted acidity of these catalysts is the lattice composition. For a zeolite to be Bronsted acidic, a proton has to connect two tetrahedra containing one tetravalent cation (often Si4+) or a trivalent cation (often Al3+). It appears that within a particular concentration region the deprotonation energy is a strong function of the Al/Si ratio. 

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