Albert R. Matlin

Ab Initio Structures for 90°-Twisted s-trans-1,3-Butadiene and Cyclooctatetraene : The Naked sp2-sp2 Bond

The bond length of a carbon-carbon sp2-sp2 sigma-bond without the perturbing effects of pi-interactions has been estimated by high level calculations on two prototypical systems: a 90 degrees -twisted form of butadiene and the tub conformer of cyclooctatetraene. The former system yields a value of 1.4818 A, considerably longer than previous estimates. The corresponding bond length in the latter is slightly shorter due to some pi-electron delocalization.

Photochemically induced reactions of cis,cis-cyclooctadienone

Abstract Irradiation of 2,7-cyclooctadienone 1 produces cis,trans-2,7-cyclooctadienone 5 which has been characterized by low temperature 13 C NMR. Dienone 5 is in equilibrium with a zwitterionic oxyallyl species 6 via B, B′ bond formation. Zwitterion 6 forms cycloadducts with ethyl vinyl ether and 2-methoxypropene.

Intramolecular photochemical reactions of 2-acyl-4-oxa-1,5-hexadienes

Abstract Photolysis of alkyl-substituted 2-(2-oxa-3-butenyl)cyclopent-2-enones gives rise to derivatives of bicyclo[2.1.1]hexanes (“rule of five” product), and α-methylenecyclopentanones(photo-Claisen rearrangement). Methyl substitution remote from the bond forming centers produces a regioselective reaction yielding only the “rule of five” product.

Intramolecular photocycloaddition reactions of 1-acyl-3-oxa-1,5-hexadienes

Abstract The regioselectivity of the intramolecular [2+2] photocycloadditions of 1-Acyl-3-oxa-1,5-hexadienes appears, in general, to follow “rule of five” closure and give annelated 2-oxa-bicyclo[2.1.1]hexanes.

Weak acidity of vinyl CH bonds enhanced by halogen substitution.

As shown by the rates of proton-deuteron exchange in ethylenes with halogen substituents, the weak acidity of vinyl CH bonds is enhanced by halogen substitution. Relative rates of exchange in basic deuterium oxide reflect the relative acidities. Substitution in the α position has the strongest effect. Less electronegative halogens such as bromine increase the acidity more than does fluorine. The vinyl CH acid strengths correlate closely with the energies of deprotonation of isolated molecules into isolated anions, as computed with the MP2/cc-pVQZ model. The smaller deprotonation energies are associated with the stronger acids. Atomic charges from a natural bond order analysis done with the MP2/aug-cc-pVQZ model show that the negative charge becomes more dispersed in the anions of the stronger acids. Results are given for 13 haloethylenes and for 6 halogen-substituted butadienes, cyclopropenes, and a cyclobutene.

Four isomeric 7-isopropyloctahydro-4H-inden-4-ones

The four isomeric 7-isopropyl-4-hydrindanones (2)–(5) have been prepared and their configurations assigned, using arguments based on the results of equilibration of the two pairs of ketones and on the products formed on hydrogenation of enone precursors. Base-catalysed equilibration at ca. 22 °C indicates that for (3)⇄(2), –ΔG 4.5 kcal mol–1 and for (5)⇄(4), –ΔG ca. 0.1 kcal mol–1. Possible diagnostic features in the 1H n.m.r. spectra of (2)–(5) are discussed briefly.