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AbstractThe essential oils from peels and leaves of Citrus clementineHort. ex Tan. were extracted via two methods: conventional hydrodistillation (CHD) and microwave-assisted hydrodistillation (MAHD). Their physicochemical properties were investigated. Their chemical compositions of the oils were determined by GC/FID and GC/MS. A total of forty-one and seventy-seven compounds of the total essential oil composition of the peels and leaves respectively were identified. The peel oils were dominated by monoterpene hydrocarbons in which limonene was the main component (95.48% [CHD], and 95.03% [MAHD]). The leaf oils were also dominated by sesquiterpene hydrocarbons with sabinene (26.02% [CHD], and 19.52% [MAHD]), β-elemene (10.50% [CHD], and 18.04% [MAHD]), linalool (9.88% [CHD], and 7.51% [MAHD]), (E)-β-ocimene (5.87% [CHD], and 5.00% [MAHD]), β-caryophyllene (4.04% [CHD], and 7.49% [MAHD]), and δ-selinene (4.76% [CHD], and 8.02% [MAHD]) as major components. The oil contents of peels were obtained with 5.31% and 5.67% by CHD method and MAHD method, respectively. The oil contents of the leaves were obtained with 0.33% and 0.20% by CHD method and MAHD method, respectively. The antimicrobial activity (disc diffusion antibiotic sensitivity assay) of the oils was investigated against six reference test organisms including two Gram (+) bacteria (Bacillus subtilis, Staphylococcus aureus), three Gram (-) bacteria (Escherichia coli, Pseudomonas aeruginosa, Shigella flexneri), and one fungus (Candida albicans).

AbstractThe chemical composition of the curry leaf essential oils obtained from curry trees growing in the South of Vietnam was studied for the first time. Two methods of extraction were used, conventional hydrodistillation (CHD) and microwave-assisted hydrodistillation (MAHD), thus leading consequently to the isolation of two oils of moderately different composition. The oils were obtained in the yields of 0.83 % and 0.39 % by CHD (480 minutes) and MAHD (50 minutes), respectively. The main chemical compositions of the oils were completely dominated by hydrocarbons. The extracted oils were determined by GC/FID and GC/ MSD to contain 76 and 62 identifiable components for the CHD and the MAHD methods, respectively. The oil extracted by MAHD displayed a higher anti-microbial activity than the oil extracted by means of CHD.

The enol-enethiol tautomerism of p/p'-disubstituted thiobenzoyl benzoyl methanes have been studied by 1H NMR spectroscopy. The significance of the chelate proton chemical shift has been evaluated by means of principal component analysis.

Deuterium isotope effects on ¹³C nuclear shielding, ⁿΔC(OD), were investigated for a series of enolic triacetylmethane, 2-acyl-1,3-cycloalkanediones, 5-acyl Meldrum’s acids and 5-acyl-1,3-dimethylbarbituric acids at different temperatures. The enolic 2-acyl-1,3-cycloalkanediones, 5-acyl Meldrum’s acids and 5-acyl-1,3-dimethylbarbituric acids all exhibit intramolecular enol–enol tautomerism. For the first two the equilibrium constants were estimated from the deuterium isotope effects on the enolic and carbonylic carbons. The equilibrium constants were estimated to be 1.5 for the enolic 2-acyl-1,3-cyclohexanediones and 2-acetyl-1,3-cyclopentanedione, favouring the form having an endocyclic enolic double bond, and 0.8 for 5-acyl-1,3-dimethylbarbituric acids, favouring the form having an exocyclic enolic double bond. Apparently, the equilibrium position is unaffected by increasing the size of the acyl group, and therefore no distinct effects caused by steric hindrance were observed. The non-hydrogen-bonded α-carbonyl group of enolic triacetylmethane, the 2-acyl-1,3-cycloalkanediones, 5-acyl Meldrum’s acids and 5-acyl-1,3-dimethylbarbituric acids cause a high frequency shift of the OH ¹H chemical shifts. A plot of the latter against the sum of ²ΔC(OD)+⁴ΔC(OD) shows a larger sum for the compounds apparently exhibiting intramolecular enol–enol tautomerism than for compounds apparently not exhibiting such tautomerism. © 1998 John Wiley & Sons, Ltd.

4-hydroxy-6-mercaptothiopyran-2-thiones in solution exhibit structural dynamics owing to occurrence of intramolecular degenerated tautomerism.

Anisole (or dimethoxy analogues) and thioanisole can be efficiently acylated under conventional or microwave conditions.

The new geranylated coumarin surangin D (I) is isolated together with four known coumarins and seven xanthones.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.