Abstract— Fluorescence and phosphorescence spectra of lumiflavine, riboflavine, FMN and FAD have been measured by continuous and flash excitation techniques. The differences in emission characteristics observed, show that the flavine side‐chains afect the singlet‐triplet transitions on which chemical and biological activity of flavine systems depend.

Abstract— Flavines in the excited state can effect anaerobic oxidation of amino acids to keto acid and ammonia. The rate of the process depends on the structure of the amino acid. These systems show similarities to the amino acid oxidases.

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Methylcyclohexane-1 : 3-dione, previously imperfectly characterised, has been made by three methods. Monoenol ethers are prepared from several cyclohexane-1 : 3-diones and (a) ethanol in presence of toluene-psulphonic acid, (b) ethyl iodide and sodium ethoxide, or (c) ethyl orthoformate and an acid catalyst. Method (a) is not applicable to %methyl-diones, and (b) is useful only with 2-methyl-diones. Method (c) is generally applicable, but under certain conditions gives complex compounds formed by the coupling of three dione molecules through a CH group.DURING experiments directed towards the synthesis of steroids and other natural have examined the preparation of certain cyclohexane-1 : 3-diones (3-hydroxycyclohex-2-enones) and their enol ethers.cycZoHexane-1 : 3-dione was most easily made by hydrogenation of resorcinol in alkaline solution, but conditions milder than those hitherto recommended were necessary to prevent further reduction. With methyl iodide and methanolic sodium methoxide it afforded the 2-methyl compound, but the maximum yield was only 58% (cf. Friedman and Robinson, Chem. and I d . , 1951, 777) ; and this was not improved by methylation in aqueous sodium hydroxide with a large excess of methyl iodide, partial ring scission to 5-ketohexanoic acid also occurring. Further methylation of 2-methylcyclohexane-1 : 3dione (in methanol) gave the enol ether ; the 2 : 2-dimethyl compound could not be isolated. In contrast, 5 : 5-dimethylcyclohexane-1 : 3-dione always gave a mixture of the 2-methyl and the 2 : 2-dimethyl derivative, as reported by Desai (J., 1932Desai (J., , 1079 and HirsjaM (Chem. A h . , 1948,42,2936). Gilling (J., 1913Gilling (J., , 2029 described the reduction of 4-methylresorcinol ; the product was believed to be 4-methylcyclohexane-1 : 3-dione, but was not satisfactorily characterised. We confirmed the formation of the 4-methyl-dione, a syrup, which rapidly oxidised in air to (crystalline) a-methylglutaric acid. The dione was characterised as the methylenebisderivative, and was synthesised by two further, interdependent methods. Methyl 4-carbe t hoxy-5-keto-2-met hylhexanoat e (from ethyl ace t oacet at e, methyl a-me t hylacrylate, and sodium ethoxide) on successive treatment with sodium ethoxide and alcoholic potassium hydroxide yielded a separable mixture of a-methylgutaric acid and the 4-methyl-dione, in proportions which varied widely in different experiments (Table 1).