Perpendicular component of dipole moment in methyl groups

Consideration of the non equivalence of hydrogen atoms in a methyl group attached to a planar moiety indicates that a component of electric dipole moment should exist in a direction perpendicular to the local C ₃ axis of the CH₃ group. Semiempirical molecular-orbital computations produced estimates of this moment and of the barriers to internal rotation which may make this moment observable.     

Mesophases II

In the continuation of a review of the classification, properties and applications of mesophases, the general features of thermodynamic data of thermotropic liquid–crystalline phase transitions are surveyed. The orientation of molecules in liquid–crystalline mesophases is discussed in relation to the electrical properties. Some applications of mesophases are outlined. After surveys of both the structural classes of lyotropic mesophases and the properties of plastic crystals in cubic phases, the thermodynamic, structural and other properties of all mesophases-are summarily considered in relation to the present state of the knowledge in this field.     

Infrared spectra of CO in absorption and evaluation of radial functions for potential energy and electric dipolar moment

From quantum-chemical calculations of rotational g factor and new experimental measurements of strengths of lines in infrared spectra of vibration–rotational bands v′–0 in absorption, with 1≤v′≤4, of ¹²C¹⁶O, and from analysis of 16,947 frequencies and wave numbers assigned to pure rotational and vibration–rotational transitions within electronic ground state X ¹Σ⁺, including new measurements of band 4–0 of ¹²C¹⁶O, we evaluate radial functions for potential energy and electric dipolar moment, the latter both in polynomial form and as a rational function that has qualitatively correct behaviour under limiting conditions. Received: 8 November 2001 / Accepted: 5 February 2002 / Published online: 14 August 2002     

Absorption spectra in the vacuum ultraviolet region of small molecules in condensed phases

With radiation from a synchrotron we measured the spectra of several small molecular species, in the solid phase at 10K, either pure--O2, NO, CO2, N2O, H2O and NH3--or, for NH3, also dispersed in Ar at molar ratio 1/250, from the onset of absorption in the ultraviolet region until the limits of transmission by crystalline LiF or solid Ar. In a quantitative treatment of spectral data, we fitted the total absorption profile divided by wavenumber to Gaussian curves of minimal number, and made tentative assignments of electronic transitions and vibrational structure by comparison with spectra of gaseous species. These results illuminate the nature of electronic spectra of samples in solid phases in the vacuum ultraviolet region.     

Fullerol cluster formation in aqueous solutions: implications for environmental release

Here we report on the characteristics of fullerol in aqueous systems and examine those conditions that affect the physical state of fullerol in water. When dispersed in water fullerol forms polydisperse suspensions characterized by both small ( approximately 100 nm) and large associations (>500 nm). These clusters are charged with a point of zero net proton charge (PZNPC) of approximately pH 3. Though the size of fullerol clusters may be manipulated through changes in solution chemistry, principally pH, cluster formation cannot be entirely prevented through these means alone. The fullerol cluster structure is amorphous as revealed by X-ray diffraction analysis, which is in contrast to clusters of C(60) formed through dissolution in toluene and then introduced into water through sonication (SONnC(60)). The SONnC(60) clusters are crystalline with a structure similar to that of unreacted C(60) crystals.     

Single-isomer iodochlorination of alkynes and chlorination of alkenes using tetrabutylammonium iodide and dichloroethane

The efficient formation of single-isomer, differentially halogenated alkenes and alkanes is described. These structures were generated by treatment of the appropriate alkyne or alkene with tetrabutylammonium iodide in refluxing dichloroethane. This process is highly selective as evidenced by control experiments using ICl. Treatment of the same alkenes and alkynes directly with iodine monochloride resulted in complex, inseparable mixtures of regio- and stereoisomers. Mechanistic studies indicated that the Bu4NI reaction most likely proceeded through the slow generation of ICl. Complexation of ICl with Bu4NI is also a key controlling element that leads to perfect regio-, chemo-, and stereoselectivity in these processes.     

A simple method to prepare single isomer tetrasubstituted olefins by successive Suzuki–Miyaura cross-couplings of E-β-chloro-α-iodo-α,β-unsaturated esters

A convenient method of synthesizing tetrasubstituted olefins as single isomers is described. E-β-Chloro-α-iodo-α,β-unsaturated esters are first converted into the corresponding E-β-chloro-α,β-unsaturated esters using Suzuki–Miyaura coupling reactions with arylboronic acids and alkenylboronic acids. These transformations gave complete selectivity, and proceeded with substitution at the more activated α-iodide position. These compounds, isolated as single isomers, were then transformed into tetrasubstituted olefins by Suzuki–Miyaura couplings with arylboronic acids, alkenylboronic acids, and alkyl boranes to afford the corresponding tetrasubstituted olefins as single isomers. During this coupling process, it was discovered that the use of small ligands, such as PMe₃ or PEt₃, was critical for efficient coupling. The stereochemistry and regiochemistry of the products were unequivocally established using NMR methods.     

Thermomorphic metal scavengers: A synthetic and multinuclear NMR study of highly fluorinated ketones and their application in heavy metal removal

The preparation of a ketone with two long chain perfluoroalkyl groups is reported via the coupling reaction of a perfluorinated alkylzinc reagent and a perfluoro-acid chloride. This ketone has been investigated in the heterogeneous removal of heavy metals M²⁺ (M = Sn, Cd, Pb, Hg) and As⁵⁺ from aqueous solutions and removal of these metals from organic solvents using the unique thermomorphic properties of the fluorous ketone. In addition, a comprehensive ¹³C NMR study of one of the intermediates in the synthesis, 2H,2H,3H,3H-perfluoronanoic acid, has allowed the determination of all ¹J_C-F and ²J_C-F coupling constants. Also reported is the crystal structure of the acid CF₃(CF₂)₅CH₂CH₂CO₂H.