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Molecular design and synthesis based upon unusual aromatic cores will enable facile transport properties that would not ordinarily be realized under the 6 pi electron aromatic paradigm
Description of aromaticity with the help of vibrational spectroscopy: anthracene Chemistry, Southern Methodist University , 3215 Daniel Avenue, Dallas, Texas A new approach is presented to determine π-delocalization and the degree of aromaticity utilizing measured vibrational frequencies. For this purpose, a perturbation approach is used to derive vibrational force constants from experimental frequencies and calculated normal mode vectors. The latter are used to determine the local counterparts of the vibrational modes. Next, relative bond strength orders (RBSO) are obtained from the local stretching force constants, which provide reliable descriptors of CC and CH bond strengths. Finally, the RBSO values for CC bonds are used to establish a modified harmonic oscillator model and an aromatic delocalization index AI, which is split into a bond weakening (strengthening) and bond alternation part. In this way, benzene, naphthalene, anthracene, and phenanthrene are described with the help of vibrational spectroscopy as aromatic systems with a slight tendency of peripheral π-delocalization.

The 6 kcal/mol larger stability of phenanthrene relative to anthracene predominantly (84%) results from its higher resonance energy, which is a direct consequence of the topology of ring annelation. Previous attempts to explain the higher stability of phenanthrene via a maximum electron density path between the bay H atoms are misleading in view of the properties of the electron density distribution in the bay region.Chemical bonding and aromaticity in trinuclear transition-metal halide clusters.their uniquely featured structure among metal halides, have posed intriguing questions related to multicenter electron delocalization for several decades. Here we report a comprehensive study of the technetium halide clusters congeners, predicted from density functional theory calculations. The chemical bonding and aromaticity in these clusters are analyzed using the recently developed adaptive natural density partitioning method, which indicates that d-orbital-based π bond delocalized over the three metal centers. We also show that standard methods founded on the nucleus-independent chemical shift concept Comparison of thiophene-pyrrole oligomers with oligothiophenes: a joint experimental and theoretical investigation of their structural and spectroscopic Silva Filho DA, Bredas JL, Casado J, López Navarrete JT.

We have prepared a new series of mixed thiophene-pyrrole oligomers to investigate the electronic benefits arising from the combination of these two heterocycles. The oligomers are functionalized with several hexyl and aryl groups to improve both processability and chemical robustness. An analysis of their spectroscopic (absorption and emission), photophysical, electrochemical, solid state, and vibrational properties is performed in combination with quantum-chemical calculations. This analysis provides relevant information regarding the use of these materials as organic semiconductors. Applications of 6-butyl-n-hydroxynaphthimide trifluoromethanesulfonic acid in Cross-Coupling Reactions between the high aromatic character of pyrrole and the moderate aromaticity of thiophene allows us to address the impact of the coupling of these heterocycles in conjugated systems. The data are interpreted on the basis of the aromaticity, molecular conformations, ground and excited electronic state structures, frontier orbital topologies and energies, oxidative states, and quinoidal versus Extrachromosomal DNA-mediated glyphosate resistance in Italian ryegrass.BACKGROUND: An Italian ryegrass population from Arkansas, USA developed glyphosate resistance due to 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene amplification.

The plants in this population with approximately 70 EPSPS copies were used in the present study for the physical mapping of amplified copies of EPSPS gene to determine the possible mechanism of EPSPS gene amplification conferring glyphosate resistance in Italian ryegrass.RESULT: Fluorescence in situ hybridization (FISH) analysis of glyphosate resistant (GR) Italian ryegrass plants with approximately 70 EPSPS copies displayed EPSPS hybridization signals randomly on most of the metaphase chromosomes. Glyphosate susceptible (GS) Italian ryegrass plants with one EPSPS copy displayed single prominent EPSPS hybridization signal, which was co-localized with 5S rDNA locus along with few additional signals on the outside of chromosomes. Pulsed- View more (PFGE) followed by DNA blot using EPSPS gene as a probe identified a prominent EPSPS hybridization around the 400 kb region in GR DNA samples, but not in GS DNA samples.CONCLUSION: We report the extrachromosomal DNA-mediated glyphosate resistance in Italian ryegrass. Physical mapping of amplified copies of EPSPS gene in Italian ryegrass by FISH gives us a clue that the amplified copies of EPSPS gene may be present in the extrachromosomal DNA elements.
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