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.

1,3-Dipolar Cycloadditions. Past and Future†

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).

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Deuterium magnetic resonance: theory and application to lipid membranes.

The trans-influence: its measurement and significance

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.

1.3‐Dipolare Cycloadditionen Rückschau und Ausblick

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...

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

NMR Spectra of Nematic Solutions of Methyl Isocyanide and Methyl Cyanide

19F magnetic shielding anisotropies of the fluoromethanes have been obtained from studies in a smectic liquid crystal solution using a pulsed FT NMR spectrometer. The value of Δσ obtained for methyl fluoride in the smectic phase is observed to be comparable in magnitude but higher in accuracy than the previous measurements obtained from theoretical, clathrate, molecular beam, and nematic single phase techniques, with the earlier value obtained using the nematic–isotropic two‐phase method being obviously in error. The shielding anisotropy measured for fluoroform is found to agree with the prior nematic two‐phase value, with the nematic single‐phase and clathrate values being considerably lower. The anisotropy measured in this investigation for methylene fluoride was found to be in disagreement with both previous values measured via molecular beam and nematic two‐phase techniques. It is shown that on transforming the experimental shielding anisotropy values obtained in this study along the C–F bond directio...

19F shielding anisotropies of the fluoromethanes obtained from NMR studies in a smectic liquid crystal solution

Phosphorus chemical shielding anisotropies and the sign of JPP IN P4S3 from NMR studies in a nematic solvent

Orientation studies by N.M.R. spectroscopy using a lyotropic liquid crystal solvent

The fluorine‐19 shielding anisotropies of CF3Cl, CF3Br, CF3I, and CF3CCl3 have been determined from analyses of fluorine NMR spectra in partially ordered smectic liquid crystal solutions. The high degree of orientation and increased solubility produced in the smectic phase leads to measurements of σ∥−σ⊥ for each of these systems to relatively high accuracy. The anisotropies obtained for the trifluorohalomethanes are found to increase in the order: CF3Cl, −13.4±0.5 ppm; CF3Br, 2.7±0.3 ppm; CF3I, 16.8±0.2 ppm. The quantity σ∥ is approximately constant for each of the CF3X molecules studied. This feature permits an estimate of the shielding and spin–rotation constants of CF4.

Benjamin P. Dailey

Papers

NMR Spectra of Nematic Solutions of Methyl Isocyanide and Methyl Cyanide

19F shielding anisotropies of the fluoromethanes obtained from NMR studies in a smectic liquid crystal solution

Phosphorus chemical shielding anisotropies and the sign of JPP IN P4S3 from NMR studies in a nematic solvent

Orientation studies by N.M.R. spectroscopy using a lyotropic liquid crystal solvent

Fluorine‐19 FT–NMR studies of CF3‐containing systems dissolved in smectic liquid crystal solutions