Oxygen quantum chemical calculations

The dipole density profile p (z) indicates ordered dipoles in the adsorbate layer. The orientation is largely due to the anisotropy of the water-metal interaction potential, which favors configurations in which the oxygen atom is closer to the surface. Most quantum chemical calculations of water near metal surfaces to date predict a significant preference of oxygen-down configurations over hydrogen-down ones at zero electric field (e.g., [48,124,141-145]). The dipole orientation in the second layer is only weakly anisotropic (see also Fig. 7). 

Bond orders, charges on the atoms in 1 l//-pyrido[2,l-Z)]quinazolin-l 1-one and its protonated form were calculated by quantum chemical calculations by the semiempirical AMI method. According to the results, the equilibrium conformation of the ring in 1 l//-pyrido[2,l-Z)]quinazolin-l 1-one is planar, while l//-pyrimido[l,2-u]quinolin-1-one adopts a conformation close to a half-chair due to the unfavorable interactions between the oxygen atom of the carbonyl group and the ring C-10 atom in the pen-position (97MI22). 

The isopyridine 179 (3<52-lH-pyridine) is the result if the oxygen atom of 180 is replaced by an NH group. Owing to the better electron-donor quality relative to that of an oxygen atom, the NH group could have the effect that the zwitterion 179-Zj is more stable than the allene structure 179, even in the gas phase. Experiments and quantum-chemical calculations support this expectation. 

For (35 R = R = COjMe) the ESR powder spectra turned out to be very sensitive to the dihedral angle of the carbonyl oxygen with respect to the ring plane (cf. quantum chemical calculations Section 4.12.2). A very small discrepancy between the angles for both C=0 groups caused spin densities on both S atoms to diverge strongly and hence S lines in the spectrum to be considerably... 

Note that 1,5-diketones 29 (Scheme 2) are cyclodehydrated as soon as they are formed, and this process evidently occurs via protonation of the carbonyl group. The proton affinity in this case is probably determined by the substituent at each carbonyl group in 29. So far, there are no synthetic investigations of the problem, whereas quantum chemical calculations reveal the equal possibility for proton addition to both oxygen atoms in homophthalic dialdehyde (86KGS460). 

Enthalpies of formation are determined experimentally in a number of ways. Perhaps the most common way is through precise oxygen combustion measurements. Where data do not exist in tabulations, estimation techniques—either empirical or based on quantum chemical calculations—are available. 

The SCs at the silica surface readily react with molecular oxygen. This reaction is convenient to monitor optically (Figure 7.23a). Oxygen chemisorption is accompanied by the disappearance of the optical absorption band of SCs. The adsorption of one molecule leads to the decay of one SC. Quantum-chemical calculations show that the three-member cyclic symmetric structure (Figure 7.24) is the most stable product of oxygen addition to the SC [74] ... 

The /ra -6-fluoro-3,6-dihydro-1,2-oxathiin 2-oxide 126 prefers a conformation in which the ring oxygen lies almost in the plane of the four carbon centers and the S=0 bond resides in a pseudoequatorial orientation. The fluorine substituent adopts a stable pseudoaxial orientation. Quantum-chemical calculations suggest a stabilizing anomeric effect which was interpreted in terms of an n0 a C-F hyperconjugative interaction <2002CEJ1336, CHEC-III(8.10.3)688>. 

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