Uses of isotopes in organic chemistry

In recent years, isotopes have become one of the most potent tools available to the organic chemist for determination of reaction mechanisms, quantitative analysis, and elucidation of structures. The purpose of this review is to illustrate a variety of tracer applications by specific examples

The Dipole Moment of Bis-(p-chlorophenylcyclopentadienyl)-iron

The dipole moment (3.12 D) found for bis-(p-chlorophenylcyclopentadienyl)-iron indicates a molecular configuration having the p-chlorophenyl groups in rather close proximity to one another

Quantum Mechanical Calculations of Electrical Effects of Substituents in para-Substituted Anilines

Base strength measurements with substituted anilines indicate direct conjugation between the amino groups and electron-attracting unsaturated substituent groups such as —NO_2,—C≡N, etc. (I). Such conjugation delocalizes the unshared electron pair of nitrogen and confers a formal (+) charge on the amino group. Somewhat analogous behavior might be anticipated for substituents which do not carry multiple bonds but which, like tercovalent boron, could accept an electron pair (II) or, like a positively charged trimethylammonium group, could stabilize an adjacent negatively charged center as in the “ylides” (III). Resonance forms may be written which symbolize each of these situations (I-III)

Small-Ring Compounds. XIV. Radioactive Cyclobutanone from Ketene and Diazomethane-^(14)C

It has been shown by the ^(14)C-tracer technique that cyclobutanone is formed from the reaction OF ketene with diszomethane-^(14)C via an intermediate possessing the symmetry properties of cyclopropanone

The Mechanism of Aminations of Halobenzenes

An elimination-addition mechanism, probably involving a "benzyne" intermediate, has been established for the rearrangements which often occur in the conversion of non-activated aryl halides to arylamines with metallic amides. The evidence for the "benzyne" intermediate was obtained through ^(14)C-tracer studies of rearrangements with halobenzenes and experiments designed to determine the role of the hydrogen atom located ortho to the displaced halogen atom

Orientation in Aminations of Substituted Halobenzenes

The respective orientations of amine and substituent groups resulting from aminations of a number of substituted halobenzenes have been determined qualitatively and correlated with the aid of a previously postulated elimination-addition (“benzyne”) mechanism

Small-ring Compounds. XXIII. The Nature of the Intermediates in Carbonium Ion-type Interconversion Reactions of Cyclopropylcarbinyl, Cyclobutyl and Allylcarbinyl Derivatives

Investigation of the extent of isotope-position rearrangement in carbonium ion-type reactions of ^(14)C-labeled cyclopropylcarbinyl derivatives has revealed that the three methylene groups of the starting material achieve a striking degree of equivalence between reactants and products. These results, taken in conjunction with the abnormally large solvolytic reactivities of cyclopropylcarbinyl and cyclobutyl halides and sulfonate esters, can best be accounted for by assuming rapid but not instantaneous equilibration of three isomeric non-classical unsymmetrical “bicyclobutonium” ion intermediates