Orientation, anomalous

T. Zavada, R. Kimmich 1998, (The anomalous adsorbate dynamics at surfaces in porous media studied by nuclear magnetic resonance methods. The orientational structure and Levy walks), J. Chem. Phys. 109, 6929. 

The other anomalous behavior was the smaller-than-expected permeability of highly branched compounds. This deviation has been explained on the basis that membrane lipids are subject to a more highly constrained orientation (probably a parallel configuration of hydrocarbon chains of fatty acids) than are those in a bulk lipid solvent. As a result, branched compounds must disrupt this local lipid structure of the membrane and will encounter greater steric hindrance than will a straight-chain molecule. This effect with branched compounds is not adequately reflected in simple aqueous-lipid partitioning studies (i.e., in the K0/w value). 

Some apparent anomalies in Table XII are the divergent results of reactions 1 and 4. In reaction 1 the alkyl sodium was generated in situ and the difference in the result may be due to the reaction of something other than the alkyl sodium. The exclusively meta dimetallation reported for reaction 4 is also anomalous since a purely inductive deactivation of the ring should give at least some of the para isomer. Another anomaly is the meta orientation in reaction 8. The nitrogen of triphenylamine is not very basic, however, and might not participate in the special mechanism proposed for reaction at the ortho position. 

Figure 6.25. Deposition temperature versus (a) elemental composition, (b) crystalline orientation, and (c) deposition rate for CuInS2 films with precursor feed rate of 1.6 g/h. In plot (a), the accuracy limit of 5% per element resulted in an anomalous overall percent composition for the In-rich, S-poor deposited material.

From gas phase measurements CO is known to prefer top sites on all three low index faces, with the CO molecule perpendicular to the surface and bonded through the carbon end of the molecule except at high coverages (27). It is likely that HCOOH and COOH are adsorbed in a similar way. It is not likely that they could "enter the "troughs , which seems to be possible for anions. For Pt(100) on the other hand, upon sweep reversal and gradual oxide reduction, anions are immediately adsorbed on that "flat" surface. They block adsorption of HCOOH. Adsorption of anions decreases as potential becomes more negative. The oxidation of HCOOH commences and the rate increases as at more negative potentials, i.e. at lower overpotential. A competition between anions and HCOOH adsorption explains this apparently anomalous behaviour. The explanation of the "anomalous behaviour of the Pt(110) surface can be also found in the data for stepped surface vicinal to the (100) and (110) orientations. 

N. Vass, "The Nature of the Alternating Effect in Carbon Chains. Pt. XXIII. Anomalous Orientation by Halogens, and Its Bearing on the Problem of the Ortho-Para-Ratio in Aromatic Substitution," JCS 131 (1928) 417425. 

An exception among organic molecules is the adsorption of thiourea since that gives no maximum on the AG° vs. plot. It was suggested " that such atypical behavior can be expected for any neutral molecule that has the normal to the surface component of the dipole moment sufficiently positive compared with the resulting dipole moment of n displaced water molecules. In the case of a TU molecule oriented with the sulfur atom toward the metal surface, the ratio of /iA// is approximately equal to 2.5 D. This value is greater than the dipole moment of water, thus fulfilling the condition of atypical behavior. The anomalous behavior of thiourea is probably due to the fact that only a few solute molecules satisfy this condition. 

Anomeric effects are cumulative, and can cause a potentially flexible ring to adjust to a more rigid conformation in order to maximize the overlap of suitable lone pair and a orbitals. It has been particularly instructive in explaining anomalous preferences for substituent orientations in tetrahydropyrans and related compounds. In the case of 2-methoxytetrahydropyran, for example, the axial conformer is three times more populated than the equatorial form (Scheme 1.2). 

The dependence of adsorption properties and texture on electrolytic palladium deposits on the deposition potential was investigated by Tsirlina et al. [116]. It was found that, in sulfuric acid solutions, the palladium dissolution, which accompanies the oxygen adsorption, obscures the adsorption behavior of the deposits with respect to oxygen. Assumptions were made about the predominant crystallographic orientation (100) of the surface of some palladium deposits being dependent on the deposition potential and about the presence of regions whose adsorption properties are anomalous with respect to copper. The assumptions are based on a comparative analysis of the copper adsorption data and x-ray diffraction patterns. In addition to sites of crystalline palladium, the deposits were found to have disordered areas as well. 

Hampshire, D., Seutjens, J., Cooley, L. and Larbalestier, D., Anomalous Suppression of Transport Critical Current Below B ,(T) in Oriented Sintered Samples of DyBa,Cu,Ov, Appl. Phys. Lett. 53 814 (1988). 

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