Cyanocarbon Chemistry. II.1 Spectroscopic Studies of the Molecular Complexes of Tetracyanoethylene

Molecular association of various aromatic hydrocarbons (D, including sterically hindered donors) with a representative group of diverse acceptors (A = quinone, trinitrobenzene, tetracyanoethylene, tropylium, tetranitromethane, and nitrosonium) is visually apparent in solution by the spontaneous appearance of distinctive colors. Spectral (UV−vis) analyses of the colored solutions reveal their charge-transfer origin (λCT), and they provide quantitative information of the intermolecular association in the form of the KDA and eCT values for the formation and visualization, respectively, of different [D,A] complexes. Importantly, such measurements establish charge-transfer absorption to be a sensitive analytical tool for evaluating the steric inhibition of donor−acceptor association. For example, the steric differences among various hindered aromatic donors in their association with quinone are readily dramatized in their distinctive charge-transfer (color) absorptions and verified by X-ray crystallography of ...

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Charge-Transfer Probes for Molecular Recognition Via Steric Hindrance in Donor-Acceptor Pairs

Comparative biochemistry of the phenolase complex.

The base-stacking patterns in over 70 published crystal structures of nucleic acid constituents and polynucleotides were examined. Several recurring stacking patterns were found. Base stacking in the solid state apparently is very specific, with particular modes of interaction persisting in various crystalline environments. The vertical stacking of purities and pyrimidines in polynucleotides is similar to that observed in crystals of nucleic acid constituents. Only partial base overlap was found in the majority of the structures examined. Usually, the base overlap is accomplished by positioning polar substituents over the ring system of an adjacent base. The stacking interactions are similar to those found in the crystal structures of other polar aromatic compounds, but are considerably different from the ring–ring interactions in nonpolar aromatic compounds. Apparently, dipole-induced dipole forces are largely responsible for solid-state base stacking. It is found that halogen substituents affect base-stacking patterns. In general, the presence of a halogen substituent results in a stacking pattern which permits intimate contact between the halogen atom and adjacent purine or pyrimidine rings. Considering differences in the stacking patterns found for halogenated and nonhalogenated pyrimidines, a model is proposed to account for the mutagenic effects of halogenated pyrimidines.

Stereochemistry of Nucleic Acids and Their Constituents. X. * Solid-state Base-Stacking Patterns in Nucleic Acid Constituents and Polynucleotides

Interactions of the DNA intercalator acridine orange, with itself, with caffeine, and with double stranded DNA.

The structures of molecular compounds exhibiting polarization bonding. II. The crystal structure of the chloranil–hexamethylbenzene complex

The structures of molecular compounds exhibiting polarization bonding. I. General introduction and the crystal structur of phenoquinone

THE nature of the molecular interaction in the formation of crystalline quinhydrones has been discussed previously by Anderson1. By comparison of preliminary crystallographic data for a number of quinhydrones, he came to the conclusion that the molecules are held together by the interaction of polar groups and polarizable aromatic substances, and that hydrogen-bond formation is not an essential structural feature, though it is not necessarily excluded. We have now been able to confirm these conclusions by a detailed structure determination of phenoquinone (which will be reported in full elsewhere), and by comparison with further preliminary data for quinhydrone and other molecular compounds of this type.

Molecular Compounds of the Quinhydrone Type

The crystal structure of the chloranil–hexamethylbenzene complex

A simple method is described whereby a crystal mounted in the usual way on an oscillation goniometer may be maintained at a temperature of -30 to 60°C for at least an hour. Liquid air in a vacuum flask is boiled by electrical heating and the cold gas is conveyed to the crystal through a well-lagged rubber tube ending in a glass tube supported about 3 mm above the crystal. The temperature may be varied by adjusting the rate of boiling of the liquid air. No precautions against ice formation are necessary.

https://iopscience.iop.org/article/10.1088/0950-7671/31/5/303/pdf

S. C. Wallwork

Papers

The structures of molecular compounds exhibiting polarization bonding. II. The crystal structure of the chloranil–hexamethylbenzene complex

The structures of molecular compounds exhibiting polarization bonding. I. General introduction and the crystal structur of phenoquinone

Molecular Compounds of the Quinhydrone Type

The crystal structure of the chloranil–hexamethylbenzene complex

A simple method of obtaining low-temperature x-ray diffraction photographs