Benjamin P. Dailey

Bio: Benjamin P. Dailey is an academic researcher from Columbia University. The author has contributed to research in topics: Liquid crystal & Anisotropy. The author has an hindex of 18, co-authored 48 publications receiving 2186 citations.

Anisotropies in carbon-13 chemical shift tensor, H-C-H bond angles and the signs of the coupling constants in 13CH3I, 13CH3Br, 13CH3Cl

Abstract: A pulsed fast Fourier transform N.M.R. spectrometer is used to investigate the temperature dependence of the 13C chemical shifts in the nematic liquid crystal solutions of the following halides: 13CH3I, 13CH3Br, 13CH3Cl. The H-C-H bond angles are accurately measured in this investigation from proton magnetic resonance studies. The signs of the coupling constants D 13CH , D HH, J 13CH and the ordering parameter have been assigned to be all positive. The 13C magnetic shielding anisotropy is found to become more positive with the increasing electronegativity of the halogen substituents. The values of the anisotropies are: Δσ = σ ∥ - σ ⊥ = - 101 ± 15 p.p.m. (13CH3I), - 10 ± 5 p.p.m. (13CH3Br), 22 ± 5 p.p.m. (13CH3Cl). Results for Δσ obtained from the slope of σn versus S 33 agree with those obtained from the nematic-isotropic phase subtraction method.

Magnetic Susceptibility of the H2O Molecule

Abstract: High‐resolution microwave spectroscopy has been used to determine the individual diagonal components of the magnetic‐susceptibility tensor of H2O. The results are: χxx = − 12.1 ± 1.6, χyy = − 13.5 ± 2.0, χzz = − 13.7 ± 1.8, all in units of 10−6 emu. The large uncertainties in these numbers arise from the small anisotropy in the magnetic susceptibility. Only a rough value of the molecular quadrupole moment can be derived from these data.

The 19F and 31P magnetic resonance spectra of phosphorus trifluoride in nematic solution

Abstract: The phosphorus and fluorine N.M.R. spectra of PF3 in a nematic solvent (EBBA) are discussed. The molecular geometry is found to agree with structures obtained from microwave and electron diffraction studies. The sign of the ordering parameter is assumed negative, the signs of the phosphorus fluorine coupling constant and of the chemical shift anisotropies follow from this assumption, and are found to be in agreement with theoretical predictions. The effect of temperature on the isotropic chemical shift of fluorine is discussed.

Studies of Chemical‐Shift Anisotropy in Liquid‐Crystal Solvents. I. Experimental Results for the Methyl Halides

Abstract: Analysis of the nuclear magnetic resonances of the methyl halides dissolved in nematic‐liquid‐crystal solutions has given measurements of the anisotropy of the proton chemical shift. The accurate determination of these anisotropies is made difficult by the effect of the liquid‐crystal solvent on the chemical‐shift measurements. The method was found to be unsuitable for the measurement of the methyl fluoride anisotropy, but the values for the other methyl halides have been determined to within ± 1.5 ppm. Methyl chloride and methyl bromide are found to have small proton chemical‐shift anisotropies indistinguishable from zero, and methyl iodide appears to have a small positive anisotropy.

1,3-Dipolar Cycloadditions. Past and Future†

Abstract: In contrast to the very large number of special methods applicable to syntheses in the heterocyclic series, relatively few general methods are available. The 1,3-dipolar addition offers a remarkably wide range of utility in the synthesis of five-membered heterocycles. Here the “1,3-dipole”, which can only be represented by zwitterionic octet resonance structures, combines in a cycloaddition with a multiple bond system – the “dipolarophile” – to form an uncharged five-membered ring. Although numerous individual examples of this reaction were known, some even back in the nineteenth century, fruitful development of this synthetic principle has been achieved only in recent years.

Deuterium magnetic resonance: theory and application to lipid membranes.

Abstract: Proton and carbon-13 nmr spectra of unsonicated lipid bilayers and biological membranes are generally dominated by strong proton–proton and proton–carbon dipolar interactions. As a result the spectra contain a large number of overlapping resonances and are rather difficult to analyse. Nevertheless, important information on the structure and dynamic behaviour of lipid systems has been provided by these techniques (Wennerstrom & Lindblom, 1977).

1.3‐Dipolare Cycloadditionen Rückschau und Ausblick

Abstract: Einer sehr grosen Zahl spezieller Synthesewege in die heterocyclische in die Reihe steht ein nur bescheidener Satz an Aufbaumethoden von allgemeiner Verwendbarkeit gegenuber. Eine erstaunliche Anwendungsbreite bei der Synthese funfgliedriger Heterocyclen kommt der 1.3-Dipolaren Addition zu. Dabei vereinigt sich der nur mit zwitterionischen Oktett-Grenzformeln wiederzugebende „1.3-Dipol” mit einem Mehrfachbindungssystem, dem „Dipolarophil”, in einer Cycloaddition zum ladungsfreien funfgliedrigen Ring. Wenngleich die Kenntnis zahlreicher Einzelbeispiele bis ins vorige Jahrhundert zuruckreicht, gelangte das Syntheseprinzip erst in den letzten Jahren zu fruchtbarer Entfaltung.

A new criterion for the determination of molecular structures from ground state rotational constants

Abstract: Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original molecule. Kraitchman's formulas represent exact solutions of the equations for the equilibrium moments of inertia. However, the effects of the zero‐point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0. These coordinates have here been called r (substitution) or rs, and it is found that rs≃(r0+re)/2, and Is= ∑ imirsi2≃(I0+Ie)/2.In the usual method of solution, the coordinate of one atom is determined from the equation for I0, and therefore the difference I0—Is must be made up by this one coordinate. This introduces a large error in the structures normally determined from ground state constants, and results in variations of 0.01 A in structures determined from different sets of isotopic species. If instead, we obtain the structure on...