Visualization and quantification of anisotropic effects on the 1H NMR spectra of 1,3-oxazino[4,3-a]isoquinolines—indirect estimates of steric compression

Local and global aromaticity under rotation: analysis of two- and three-dimensional representative carbon nanostructures

Nanoscaled 2D and 3D carbon structures with closed curved π-surfaces are of relevance in the development of desirable building units for materials science. Such species are able to sustain local and global aromatic circuits involving isolated regions or the overall structural backbone, respectively. Here we account for local and global aromaticity under rotation of representative two- and three-dimensional species involving para-connected and fused edge-sharing phenyl rings ([8]CPP, [10]CPP, CNB), and C₆₀ fullerene at different charge states. Our results denote that nanoscaled 2D global aromatics mimic the behaviour of the most prototypical aromatic 6π-circuit, given by benzene, where the shielding cone properties vary along the rotation motion. In contrast, 3D spherical aromatics remain almost invariant under rotation, given the distinctive characteristics of such species, differing from 2D global aromatics. Dissection of orbital contributions reveals that π-orbitals are determinants for shifting from non-aromatic to spherical aromatic species. Under rotation, the variation of the anisotropic effect inherent to such nanoscaled structures is accounted for, which is relevant to rationalize variation in NMR signal shifts upon the formation of host-guest aggregates.

Enabling dual aromaticity in fused nanobelts: evaluation of the magnetic behavior of fused [10]CPP units

Cyclo-para-phenylene (CPP) nanobelt structures with curved π-surfaces are of relevance in the development of desirable building units for materials science.

NMR spectral study of some 2r,6c-diarylpiperidin-4-one (3'-hydroxy-2'-naphthoyl)hydrazones with special reference to γ-syn effect

1H and 13C NMR spectra have been recorded for 2r,6c-diarylpiperidin-4-one (3'-hydroxy-2'-naphthoyl)hydrazones 10-17 and 3,3-dimethyl-2r,6c-bis(p-methoxyphenyl)piperidin-4-one (5). For selected compounds 2D NMR spectra have been recorded. The spectral data along with those reported for related compounds are used to study the effect of a heteroatom X on the 13C chemical shift of a γ-carbon with X Cα Cβ Cγ torsional angle close to 0°, termed as γ-syn effect. Also γ-gauche and δ-effects of the alkyl groups at C-3 on the carbons of the aryl group at C-2 have been studied. The chemical shifts for the naphthalene ring are in accord with the mesomeric and steric effects of the carbonyl and hydroxy groups.