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The configurational isomers of the title compounds consist of four fused five-membered rings. They contain tightly coupled 1H NMR spin systems, which provide excellent models for establishing the relationships between coupling constants and conformation. Complete chemical shift assignments and spin–spin coupling constants are reported for the title compounds by using high-field (500 MHz) 1H NMR techniques (e.g., 2D homonuclear and heteronuclear experiments, difference NOE enhancements, and computational spin simulations). In addition to the more familiar two- and three-bond couplings, the spectra of 1 and 2 also contain a number of long-range (four- and five- bond) couplings, which provide a stringent test of Barfield's theoretical treatment of four-bond couplings.

The dimerization of triquinacene (C10H10) to dodecahedrane (C20H20) has been a goal of organic chemists for more than three decades. An attempted synthesis of dodecahedrane from triquinacene using high pressure and near-UV radiation was not successful, but both hydrocarbons survived the 15 GPa treatment. There is no evidence for a pressure-induced transition in either of the materials. The results of high-pressure Raman spectroscopic investigations to 20 GPa on triquinacene and dodecahedrane are reported. Liquid triquinacene crystallizes near 0.2 GPa at 295 K and the Raman peaks associated with the molecular modes sharpen strikingly. In the crystal the external mode peaks exhibit a large pressure dependence, as expected, but the surprising fact is that the C—H stretching modes behave likewise. In dodecahedrane a similar effect is observed for the C—H stretching modes, but no external mode peaks are observed. The Raman data on dodecahedrane are compared with earlier results and calculations, which support the Ih symmetry for the molecule and an fcc lattice for the crystal.

The intramolecularly H-bonded cis enolic form of malondialdehyde in chloroform is converted to an intermolecularly H-bonded trans enol by methoxy compounds such as methanol and 3,3-dimethoxypropanal. «Polar impurities» such as acetone and dioxane do not induce this effect

Branching at a point is defined in terms of the degrees of the central points in the star graphs, K 1, n , n =0,1,2,3,…. As atoms are added to a structure (i.e., as points are added to a graph), the new structure in which the atom has been affixed to the precursor atom with the higher degree is the more branched. A branching index consistent with this axiom is B M = B R + B s + r + s , where B M , B R , and B S are the branching indices of the new structure and two precursor structures, respectively, and r and s are the degrees of the precursor atoms before they are connected by a bond (line). If B M =0 for methane, then for other molecules it is simply equal to the number of pairs of adjacent bonds, or the number of lines in the line graph of the line graph of the molecular graph. The iterated line graphs are then used to obtain a more complete ordering. Our results are compared to those of other approaches and help clarify branching and its relation to chemical properties such as boiling point.