DEPROTONATION ENERGY CALCULATION

However, if it is known that the surface hydroxyl groups under study are free, i.e. that hydrogen bonding can be excluded, the measurement of activated (unloaded) samples would be preferred in any case since the error of the deprotonation energy calculated by the use of Eq. 8 is considerably smaller than the error of both methods based on the use of probe molecules. 

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 titration coordinates evolve along with the dynamics of the conformational degrees of freedom, r, in simulations with GB implicit solvent models [37, 57], An extended Hamiltonian formalism, in analogy to the A dynamics technique developed for free energy calculations [50], is used to propagate the titration coordinates. The deprotonated and protonated states are those, for which the A value is approximately 1 or 0 (end-point states), respectively. Thus, in contrast to the acidostat method, where A represents the extent of deprotonation, is estimated from the relative occupancy of the states with A 1 (see later discussions). The extended Hamiltonian in the CPHMD method is a sum of the following terms [42],... 

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

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. 

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

Figure 21-17. The stabilization energy (E b) in anionic uracil-alcohol complexes vs the deprotonation energy (EDP) of ROH. All properties calculated at the B3LYP/6-31+-t-G (5d) level of theory (Figure 6 of ref. [48], Reprinted with permission. Copyright 2005 American Chemical Society.)...

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