Part 1 In an attempt to clarify a botanical classification problem, the chemical constituents of Ptaeroxylon obliquum were investigated. Structures ore proposed for three chromones and four coumarins isolated from the timber. Two novel chromones, Karenin and desoxykarenin (ptaeroxylin), have been shown to possess a seven-membered oxide ring fused to a 5-hydroxy-2-methylchromono nucleus. The linear direction of fusion was uniquely defined by the isolation of dihydropeucenin as a hydrogenolysis product of both Karenin and desoxykarenin. Peucenin was also isolated and its structure confirmed. The functionality and position of substituents for the coumarins was derived from spectral data. The structure of 7-0-(3,3-dimethylallyl)scopolotin was verified by acid hydrolysis to scopoletin and synthesis from aesculin. Two further coumarins, nieshoutin and nieshoutol, from spectral behaviour, are very similar; both possess a fused trimethyldihydrofuran system but have not been related chemically. On biogenotic and other evidence, structures have been proposed and a recent synthesis in this laboratory confirms the constitution of the former. Part2 A systematic study of the carbonyl and hydroxyl regions of the infrared solution spectra of twenty-seven chromones has been undertaken. The results of a qualitative survey of the effects of progressive structural changes on the spectral profile of the carbonyl region are presented. Although the hydroxyl stretching frequencies were easily identified, the complexity of the carbonyl spectrum did not allow a unique assignment of the carbonyl stretching frequency. Variation of solvent polarity and temperature proved to be of little value in this assignment. The spectra of seven chromones containing a deuterium-enriched 5-hydroxyl group indicated that two maxima, ca. 1660 and ca, 1630 cm.-1, had high carbonyl character. The possible dependence of spectral splitting on an intramolecular vibrational effect (Fermi resonance) is discussed with reference to two nuclearly deuterated derivatives of 5-hydroxy-2-mothylchromone and to oxygen-18 enriched 5-hydroxy--- 2-methylchromone
