Quantum mechanical stabilization

F. Photochromism or phototropism. In many compounds, light induced reversible colour change is observed. Such light induced reversible transitions lead to states with quantum-mechanical stability but thermodynamic instability... 

On the other hand, the proton potential of the 5-bromo compound is exactly symmetrical with reference to the reaction coordinate of the tautomerization. Consequently, the proton transfer can proceed through the tunnelling mechanism. This is the reason why the paraelectric behaviour is maintained even at 4 K. The suppression of the antiferroelectric phase transition may be derived from a quantum tunnelling effect. Such paraelectric behaviour can be regarded as quantum paraelectricity , which is a notion to designate the phenomenon that (anti)ferroelectric phase transitions are suppressed even at cryogenic temperatures due to some quantum-mechanical stabilization, proton tunnelling in this case. 

Resonance stabilization is a quantum mechanical effect it is discussed further in Section 3.12. 

Devillanova and coworkers have also addressed this issue with some simple thiones and selones. Using spectroscopic analysis and quantum mechanical calculations, they examined the various possible reaction pathways shown in Fig. 5 [72,183]. The geometries and relative stabilities of the charge-transfer and T-shaped hypervalent adducts were compared using DFT cal-... 

In a few instances, quantum mechanical calculations on the stability and reactivity of adsorbates have been combined with Monte Carlo simulations of dynamic or kinetic processes. In one example, both the ordering of NO on Rh(lll) during adsorption and its TPD under UHV conditions were reproduced using a dynamic Monte Carlo model involving lateral interactions derived from DFT calculations and different adsorption... 

The stabilization of the radical cation by forming a polaron is a trade-off between its delocalization and the energy required to distort the DNA structure. The former lowers the kinetic energy of the intrinsically quantum mechanical migrating radical cation, and the latter will be determined by factors that are independent of specific base sequence, such as the force constants of bonds in the sugar diphosphate backbone. 

Molecular mechanics calculations have become a well established tool in the area of coordination chemistry, including the coordination chemistry of nickel375-379 where they are often applied for the analysis or the prediction of structures,380 the computation of isomer or conformer ratios and metal ion selectivities,381,382 and for simulating spectroscopic properties in combination with AOM calculations or by hybrid quantum mechanics/molecular mechanics (QMMM) methods.383,384 Details of the various approaches, e.g., the incorporation of d-electron stabilization energy... 

A recent ab initio quantum mechanical study (Han et al, 1998) used B3LYP/6-31G density functional theory to examine the relative stabilities of eight conformers of AAMA with four explicit water... 

What is the origin of the energy difference between the polyproline II and /J-strand backbone conformations Brant and Flory (1965b) emphasize the important roles of steric clash, dipole-dipole interactions (see also Avbelj and Moult, 1995), and the torsional potentials governing rotation about the backbone ,t/i angles (see also Flory, 1969). An ab initio quantum mechanics study (Han et al., 1998 see also references therein to earlier work) finds that solvation by water is important. The authors examine the predicted stabilities of eight conformers of... 

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