CH overtones in acetophenone and benzaldehyde: aryl and methyl local modes

Abstract

Even though there is great practical benefit from evidence that ideal theories are reasonable approximations at small separations (10-30 A) where these relations are expected to fail, we should not be lulled into complacency. Why do not we observe major deviations from ideality due to structure of the solvent, finite ion size, correlations, and fluctuations? What is the origin(s) of the short-range repulsion and its decay at large separations? Furthermore, does the exponential form for the close-range repulsion hold at very close proximity? The power-law attraction should overwhelm the repulsion to cause a precipitous collapse. Clearly, stiff-steric interactions must exist which are of ultimate importance ARTICLES in lamellar phase instability and bilayer coalescence at extreme dehydration. Vibrational overtone spectra of acetophenone and benzaldehyde in the visible and near-infrared regions are studied by the dual beam thermal lens and the conventional near-infrared absorption techniques. The observed increase in the mechanical frequency of the aryl CH bond from that of benzene is attributed to the decrease in the aryl CH bond length caused by the electron-withdrawing property of the substituents. Overtone spectra also demonstrate that acetophenone contains two types of methyl CH bonds arising from the anisotropic environments created by oxygen lone pair and carbonyl P electrons. The local-mode parameters of the two types of CH bonds are compared with those of acetone and acetaldehyde. The possible factors influencing the methyl CH bonds in acetophenone are discussed. Acknowledgment. This work was supported by the Medical CH Overtones in Acetophenone and

Physical properties of surfactant bilayer membranes: thermal transitions, elasticity, rigidity, cohesion and colloidal interactions

“…For the phospholipids SOPC and POPE, A, is estimated to be about 1.2 X 10'14 erg and about 3 X 10"14 erg for the sugar-lipid DGDG. The layered model reduces the cumulative value for the attraction coefficient and leads to reasonable magnitudes for all coefficients (< [10][11][12][13] erg).…”

“…Again because of micromechanical technology, it is possible to directly measure the cumulated free energy potential for assembly (adhesion) of membrane surfaces to stable contact. 3,[9][10][11][12] In this article, we discuss how mixtures of lipids, cholesterol, and polypeptides affect the thermal-mechanical and colloidal interaction properties of bilayer membranes. We outline prominent…”

“…Lower "sub-" transitions have been identified and are currently under investigation.30-31 Saturated chain PCs exhibit L^-, P^, and La phases. For example, dimyristoylphosphatidylcholine (DMPC) below [10][11][12][13] eC is a Lg solid at equilibrium, a solid above 13 °C but below 24 °C, and a La liquid surface above 24 °C.32 Figure 3 shows (24) Servuss, R. M.; Harbich, W.; Helfrich, W. Bioehim. Biophys.…”

CH local mode overtone excitations in benzyl chloride—A conformational study

“…The chopped dye laser beam (SO-I00mW) creates a pulsating thermal lens in the sample (path length 1 cm~ The intensity modulations on a probe He-Ne laser beam (2 m W) passing through the sample are synchronously detected and normalized for pump laser power variation. The details of our thermal lens experimentation are given elsewhere [13]. The near infrared absorption spectrum is recorded in a Hitachi 3410 spectrophotometer from pure liquid with air as reference and path length 1 cm.…”

“…Thus overtone spectroscopy has become an effective tool for structural studies of organic molecules pertaining to nonequivalent CH bonds; the nonequivalence may arise due to factors like structural difference, conformational difference, anisotropic environments created by lone pair and/or It electron interactions etc. [4][5][6][7][8][9][10][11][12][13]. Overtone spectroscopy has also been used to study the influence of various substituents on benzene ring CH bonds [8,9,[14][15][16][17][18][19].…”