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†

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

Stereochemistry of reaction paths at carbonyl centres

Unimolecular electrical rectification in hexadecylquinolinium tricyanoquinodimethanide

In this report, which is complementary to that of Bleaney and Stevens in Reports on Progress in Physics, Volume XVI, paramagnetic resonance data are collected together for crystalline solids containing ions of the transition groups, and those parts of the theory necessary for an understanding of the results are presented in a fairly simple way. After a brief introduction, the magnetic properties of various types of compounds are considered, and a simple discussion is given of the spin Hamiltonian which is used to describe the lowest energy levels. Some details are also given of the structures of the ten crystal types which are most commonly used, and of the relation between the structure and the resonance spectrum of a single crystal. Finally, the resonance data which are available for ions of the 3d, 4d, 5d, 4f and 5f transition groups are tabulated. These data are expressed as values of the parameters in the appropriate spin Hamiltonian, and, where applicable, formulae are given for (1) energy levels, (2) susceptibility, (3) specific heat tail CT2/R, in terms of these parameters.

https://iopscience.iop.org/article/10.1088/0034-4885/18/1/308/pdf

Paramagnetic Resonance II

Sufficient isotopic combinations have been studied to make complete structural determinations of fluoroform and chloroform from microwave rotational spectra. The dimensions of CHF3 are dCH = 1.098A, dCF = 1.332A, and ∠FCF = 108°48′; those of CHCl3 are dCH = 1.073A, dCCl = 1.767A, and ∠ClCCl = 110°24′. Measurements were made on only the most abundant isotopic species of CH3CCl3. If the CCl3 configuration as in chloroform and the CH3 configuration as in methane are assumed, the CC distance in CH3CCl3 is found to be 1.55A.

Microwave Spectra and Molecular Structures of Fluoroform, Chloroform, and Methyl Chloroform

The following molecular electric dipole moments, in Debye units, have been obtained from the Stark effect of pure rotational spectra observed in the microwave region: 0.234±0.004 for NF3; 1.03±0.01 for PF3; 1.77±0.02 for POF3; 3.00±0.02 for HCN; 3.92±0.06 for CH3CN; 3.83±0.06 for CH3NC; 1.79±0.02 for CH3F; 0.75±0.01 for CH3CCH; 1.26±0.01 for SiF3H. All values apply to the ground vibrational state.

Electric Dipole Moments of Several Molecules from the Stark Effect

Four low‐J rotational transitions of 0316 have been measured in the region from 42 to 118 kmc. The rotational spectroscopic constants found are A = 106,530.0±1.1 Mc, B = 13,349.06±0.06 Mc, C = 11,834.3±1.1 Mc. The oxygen nuclei form an isosceles triangle with an apex angle of 116°49′±30′, and the two equal internuclear distances are 1.278±0.003A. From the Stark splitting of the 20,2→11,1 transition the dipole moment is 0.53±0.02 debye. Zeeman splittings of this transition show that ozone is not significantly paramagnetic.

The Molecular Structure, Dipole Moment, and g Factor of Ozone from Its Microwave Spectrum

Paramagnetic resonance has been observed in ${\mathrm{U}}^{+3}$ and ${\mathrm{U}}^{+4}$ ions in powdered samples of U${\mathrm{F}}_{3}$ and U${\mathrm{F}}_{4}$, respectively. The resonance curve in U${\mathrm{F}}_{3}$ was found to be asymmetric, with two unresolved peaks yielding ${g}_{\ensuremath{\perp}}\ensuremath{\approx}2.1$ and ${g}_{\mathrm{II}}\ensuremath{\approx}2.8$. The resonance is broad and weak; the over-all half-width is about 5 kilogauss at room temperature. The curve obtained for U${\mathrm{F}}_{4}$ is symmetric and yields $g={2.1}_{5}$. Its half-width is about 3.5 kilo-gauss at room temperature. Although the resonance in U${\mathrm{F}}_{3}$ appeared somewhat stronger at liquid air than at room temperature, that in U${\mathrm{F}}_{4}$ could be detected only at room and at elevated temperatures. The results favor the interpretation that the two unpaired electrons in ${\mathrm{U}}^{+4}$ are $6d$ electrons, that the crystalline field in U${\mathrm{F}}_{4}$ is essentially cubic, and that either the lowest component of the Stark multiplet is a nonmagnetic singlet or that the electrons have a high degree of antiferromagnetic alignment. The results on U${\mathrm{F}}_{3}$ show that the crystalline field has an axially symmetric component.

Paramagnetic resonance in uranium salts

In this paper emissions of 5577 A and 6300 A lines of OI in Martian atmosphere have been investigated. It has been found that for the 5577A line there are two peaks at 90 and 120 km and its total intensity is  about 3.5 kR. For the 6300A line, since the rate of quenching by CO2 molecules is not known, its emission profile is obtained for two values of quenching coefficient, namely, 1 X 10-13 cm3 sec-1 and 1 X 10-12 cm-3 sec-1. It has been found to have a broad peak at 100-.140 km. Its intensity has been found to be 3 and 1 kR for the two values of rate coefficient.

/pdf/day-airglow-emissions-of-5577-a-and-6300-oi-lines-in-martian-qz181us9.pdf

S. N. Ghosh

Papers

Microwave Spectra and Molecular Structures of Fluoroform, Chloroform, and Methyl Chloroform

Electric Dipole Moments of Several Molecules from the Stark Effect

The Molecular Structure, Dipole Moment, and g Factor of Ozone from Its Microwave Spectrum

Paramagnetic resonance in uranium salts

Day airglow emissions of 5577 A and 6300 OI lines In Martian atmosphere