Chemical Constituents of Rhododendron lepidotum
Two new coumarin glycosides, 7-O-β-D-glucopyranosyl-8-methoxybenzopyranone (1) and 7-hydroxy-8-O-β-glycosylbenzopyranone ((2), are reported along with the isolation of 7,8-dihydroxy coumarin (daphnetin) from Rhododendron lepidotum (aerial part).
New coumarin glycosides from Rhododendron lepidotum.
Two new coumarin glycosides, named Rhodonin (1) and Rhodonetin (2) were isolated from the aerial parts of Rhododendron lepidotum.
Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules
The NICSzz-scan curves of aromatic organic, inorganic and “all-metal” molecules in conjunction with symmetry-based selection rules provide efficient diagnostic tools of the σ-, π- and/or double (σ + π)-aromaticity. The NICSzz-scan curves of σ-aromatic molecules are symmetric around the z-axis, having half-band widths approximately less than 3 A with the induced diatropic ring current arising from Tx,y-allowed transitions involving exclusively σ-type molecular orbitals. Broad NICSzz-scan curves (half-band width approximately higher than 3 A) characterize double (σ + π)-aromaticity, the chief contribution to the induced diatropic ring current arising from Tx,y-allowed transitions involving both σ- and π-type molecular orbitals. NICSzz-scan curves exhibiting two maxima at a certain distance above and below the molecular plane are typical for (σ + π)-aromatics where the π-diatropic ring current overwhelms the σ-type one. In the absence of any contribution from the σ-diatropic ring current, the NICSzz(0) value is close to zero and the molecule exhibits pure π-aromaticity.