The Conservation of Orbital Symmetry

Die Erhaltung der Orbitalsymmetrie

A novel mechanophore with acid-releasing capability is designed to produce a simple catalyst for chemical change in materials under mechanical stress. The mechanophore, based on a gem-dichlorocyclopropanated indene, is synthesized and used as a cross-linker in poly(methyl acrylate). Force-dependent rearrangement is demonstrated for cross-linked mechanophore samples loaded in compression, while the control shows no significant response. The availability of the released acid is confirmed by exposing a piece of insoluble compressed polymer to a pH indicator solution. The development of this new mechanophore is the first step toward force-induced remodeling of stressed polymeric materials utilizing acid-catalyzed cross-linking reactions.

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Proton-Coupled Mechanochemical Transduction: A Mechanogenerated Acid

Cyclobutarenes and Related Compounds

Recent chemistry of benzocyclobutenes

7-Deuterocycloheptatriene - prepared from tropylium bromide and lithium aluminium deuteride in 94% isotopic purity - rearranges on heating at 100-140°. Mass spectrometry and proton magnetic resonance (NMR) spectroscopy showed that by an intramolecular process a mixture of the 7-, α-, β- and γ-monodeuterocycloheptatrienes is formed. The changes in shape and intensity of the NMR signals proved that these isomers arise in successive steps, each of which involves a trans-annular 1-5 shift of hydrogen, combined with a shift of two double bonds. The Arrhenius parameters of the shift are E = 31-32 kcal/mole and log A (s−1) = 10.9-11.5. In transition-state theory this corresponds with an appreciable negative entropy of activation, indicating a rigid transition state.



A number of known isomerizations in 7-membered ring systems, particularly those of the Buchner esters and acids, can be explained by a trans-annular 1-5 shift.

The chemistry of cycloheptatriene: Part VII: Thermal isomerization of 7‐deuterocycloheptatriene by trans‐annular 1‐5 shifts of hydrogen

7-Phenylcycloheptatriene-1,3,5 rearranges on heating to a mixture of the 3-, 1- and 2-isomers. These are formed in the order indicated by successive trans-annular 1-5 shifts of hydrogen. The isomerization of the 7- to the 3-isomer, by which the trienic and aromatic systems enter into conjugation, is appreciably faster than the 1-5 shift in cycloheptatriene itself. The interconversion of the 3- and 1-isomers, however, proceeds at a rate comparable with that of the unsubstituted compound.



The nature of the solvent has no influence on the rate of the 1-5 shift.

The chemistry of cycloheptatriene: Part VIII: Transannular 1‐5 shifts of hydrogen in phenylcycloheptatriene

The photo-isomerization of 7-deutero- and several phenyl-substituted cycloheptatrienes has been investigated.

The chemistry of cycloheptatriene: Part X: Photochemical shift of hydrogen in cycloheptatrienes

Eine neue Synthese des Tropons (Vorläufige Mitteilung)

cf. CA 63, 457a. The effect of substituents on 1-5 intramol. shifts of H in cycloheptatriene (I) was investigated at 100-140 Deg (CA 59, 14771b). Conversion of 7-substituted I to the 3-substituted isomer was accelerated by all of the substituents studied, including NMe2, OMe, SMe, Me, Ph, and CN, the rates varying between 700 for the NMe2 deriv. and 9 for the Me deriv. relative to the half-rate for unsubstituted I. Rates for conversion of 3-to 1-, 1- to 3-, 1- to 2-, and 2- to 1-substituted I were also measured. The 7-Me2N compd. was converted by 2 rapid and virtually irreversible steps to the 1-substituted compd., which was the only detectable isomer in the equil. mixt. At equil. the amts. of isomers decreased in the order 1-, 3-, 2-, 7- for electron-donating substituents, the differences being more pronounced as the electron-donating tendency became stronger. In this sequence the substituent is in formal conjugation with 3, 2, 1, and 0 double bonds, resp., of the trienic system. For Ph and CN substituents the 1-isomer was again the most prevalent, but the 3- and 2-isomers were present in equal amts. at equil. 7-Di-methylaminocycloheptatriene not only underwent a 1-5 H shift at 70-110 Deg but also yielded 5-7% benzene, the amt. of which increased slightly with increasing temp. Neither reaction was affected by the type of solvent used. [on SciFinder (R)]

A. P. ter Borg

Papers

The chemistry of cycloheptatriene: Part VII: Thermal isomerization of 7‐deuterocycloheptatriene by trans‐annular 1‐5 shifts of hydrogen

The chemistry of cycloheptatriene: Part VIII: Transannular 1‐5 shifts of hydrogen in phenylcycloheptatriene

The chemistry of cycloheptatriene: Part X: Photochemical shift of hydrogen in cycloheptatrienes

Eine neue Synthese des Tropons (Vorläufige Mitteilung)

The Chemistry of Cycloheptatriene Part XII: The thermal behaviour of substituted cycloheptatrienes: Preliminary communication†