Novel aromatic species containing group 14 atoms

2008 ◽  
Vol 80 (3) ◽  
pp. 563-569 ◽  
Author(s):  
Robert West
Keyword(s):  
Raman Spectroscopy ◽  
Chemical Shift ◽  
Molecular Orbital ◽  
Mo Calculations ◽  
Group 14 ◽  
Nucleus Independent Chemical Shift ◽  
Benzene Rings ◽  
Aromatic Species ◽  
Nics Calculations ◽  
Stabilization Energies

The dianions of tetraphenylsilole and tetraphenylgermole behave as aromatic species, as shown by the equalization of C-C bond lengths in these rings and by nucleus-independent chemical shift (NICS) calculations. Similarly, the dianions of 9-silafluorene and 9-germafluorene are aromatic. In the latter species, the heteroatom five-membered rings are more aromatic than the attached benzene rings. Also to be recognized as aromatically stabilized compounds are the stable unsaturated diiminocarbenes, diiminosilylenes, and diiminogermylenes. Evidence for the aromatic delocalization in these molecules comes from NMR, NICS calculations, Raman spectroscopy, isodesmic molecular orbital (MO) calculations, and calculated isomerization stabilization energies. From the presently available evidence, the aromaticity appears to alternate, with C > Ge > Si, going down group 14.

Synthesis and electronic properties of meso-tetra(3,4,5-trimethoxy)phenyl-porphyrin and -tetrabenzoporphyrin and their phosphorus complexes

2020 ◽  
Vol 24 (01n03) ◽  
pp. 105-111
Author(s):  
Taniyuki Furuyama ◽  
Yuichi Takahashi ◽  
Tomoteru Fukumura ◽  
Ana C. C. Bacilla ◽  
Nagao Kobayashi
Keyword(s):  
Chemical Shift ◽  
Molecular Orbital ◽  
Electronic Absorption ◽  
Current Density ◽  
Magnetic Circular Dichroism ◽  
Induced Current ◽  
Mo Calculations ◽  
Metal Free ◽  
Nucleus Independent Chemical Shift ◽  
Td Dft

meso-Tetra(3,4,5-trimethoxy)phenyl-porphyrin and -tetrabenzoporphyrin and their phosphorus complexes were synthesized and their electronic absorption and magnetic circular dichroism (MCD) spectra discussed based on TD-DFT molecular orbital (MO) calculations. Nucleus-independent chemical shift (NICS) and anisotropy of the induced current density (ACID) calculations were also carried out for metal-free (and phosphorus) tetrabenzoporphyrins in order to discuss the aromaticity and flow of electrons in the molecule.

Antiaromatic ions and their value in quantifying aromaticity, as probes of delocalization, and potential as stable diradicals

2012 ◽  
Vol 84 (4) ◽  
pp. 1101-1112 ◽  
Author(s):  
Nancy S. Mills
Keyword(s):  
Chemical Shift ◽  
Molecular Orbital ◽  
Energetic Properties ◽  
Nucleus Independent Chemical Shift ◽  
Highest Occupied Molecular Orbital ◽  
Diradical Character ◽  
Aromatic Species ◽  
Lowest Unoccupied Molecular Orbital ◽  
Homo Lumo

Antiaromatic dications and dianions are available through oxidation or reduction of unsaturated precursors as well as through ionization of diols. Their experimental accessibility allows them to be used to evaluate the effectiveness of theoretical treatments of antiaromaticity such as the nucleus-independent chemical shift (NICS). Because measures of antiaromaticity are generally larger in magnitude than corresponding measures of aromaticity, they demonstrate relationships between different measures of aromaticity–antiaromaticity, such as those based on magnetic and energetic properties, more effectively than do aromatic measures. Antiaromatic species are more sensitive probes of delocalization than are aromatic species, giving the possibility of observation of subtle effects. Antiaromatic species possess a small highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO-LUMO) gap, giving rise to species with diradical character.

scholarly journals Synthesis, structure and aromaticity of carborane-fused carbo- and heterocycles

2018 ◽  
Vol 9 (8) ◽  
pp. 2284-2289 ◽  
Author(s):  
Tek Long Chan ◽  
Zuowei Xie
Keyword(s):  
Chemical Shift ◽  
Molecular Orbital ◽  
Ring System ◽  
Membered Ring ◽  
Stabilization Energy ◽  
Molecular Structures ◽  
Aromatic Character ◽  
Nmr Data ◽  
Nucleus Independent Chemical Shift ◽  
System P

The results of molecular structures, NMR data, and NICS (nucleus-independent chemical shift) and ISE (isomerization stabilization energy) values as well as molecular orbital analyses clearly suggest the presence of considerable aromatic character in the exo five-membered ring of carborane-fused carbo- and heterocycles and considerable conjugation between a 3-D carborane and a fused 2-D π-ring system.

scholarly journals Aromatic, or Antiaromatic, That Is the Question:

2021 ◽  
Author(s):  
Ben Joseph R Cuyacot ◽  
Cina Foroutan-Nejad
Keyword(s):  
Electronic Structure ◽  
Chemical Shift ◽  
Model System ◽  
Low Energy ◽  
Software Packages ◽  
Ring Currents ◽  
Nucleus Independent Chemical Shift ◽  
Simple Protocol ◽  
Aromatic Species ◽  
Stable Structures

The term aromaticity in chemistry is reminiscent of symmetric, stable structures that have delocalized electrons and sustain diamagnetic ring currents in the presence of external magnetic fields. The two latter characteristics sometimes mistakenly are thought to be the same. In a groundbreaking discovery Liddle and co-workers synthesized a D3h complex with rare Th‒Th bonds. Studying the electronic structure of a neutral singlet model system, 3”, showed that the molecule has a delocalized HOMO between three Th atoms akin to a 2-electron 3-center bond. Employing nucleus independent chemical shift (NICS) computations and according to the pattern of the NICS scan plot on 3”, the authors suggested that the molecule is a σ-aromatic species as it is reflected also in the title of their paper. Unfortunately, NICS is an inappropriate tool for evaluation of the magnetic aromaticity among early and mid-transition metals (TM), the elements that share a characteristic with thorium; they all have low-energy unoccupied orbitals. In the following we explain why NICS fails to assess aromaticity of molecules containing TMs and prove that the Th3 ring is a weakly antiaromatic system. We introduce a simple protocol to examine the aromaticity of any molecule utilizing software packages, which have been used by the authors of the main article.

Synthesis, Optical Properties, Structures and Molecular Orbital Calculations of Subazaporphyrins, Subphthalocyanines, Subnaphthalocyanines and Related Compounds

1999 ◽  
Vol 03 (06) ◽  
pp. 453-467 ◽  
Author(s):  
NAGAO KOBAYASHI
Keyword(s):  
Molecular Orbital ◽  
Magnetic Circular Dichroism ◽  
Soret Band ◽  
Ring Expansion ◽  
Molecular Orbital Calculations ◽  
Mo Calculations ◽  
Key Points ◽  
Adsorption Data ◽  
Ring Expansion Reaction ◽  
Related Compounds

The synthesis of and spectroscopic data on subazaporphyrins, subphthalocyanines, subnaphthalocyanines and their related compounds reported to date are summarized, together with the results of molecular orbital (MO) calculations from our laboratory. Thus the problems and key points in the synthesis of these subazamacrocycles and their electronic absorption and magnetic circular dichroism (MCD) spectra are discussed, together with those of the monosubstituted-type low-symmetrical phthalocyanines obtained by their ring expansion reaction. The Q bands of these subazamacrocycles are orbitally doubly degenerate, and in the Soret band region, three transitions to the orbitally degenerate state are found. The MO calculations suggest that the HOMO levels destabilize considerably while the LUMO levels change slightly with increasing size of the π system. In addition, the electronic adsorption data are reproduced by the calculation only when the two pyrrole hydrogens in the monosubstituted-type phthalocyanines are assumed to be linked to the two pyrrole nitrogens along the short axis.

scholarly journals Étude théorique de la structure du phosphate d'isaxonine

1984 ◽  
Vol 62 (4) ◽  
pp. 680-686
Author(s):  
Jean-Pierre Monti ◽  
Marcel Sarrazin ◽  
Pierre Brouant
Keyword(s):  
Chemical Shift ◽  
Molecular Orbital ◽  
Coupling Constants ◽  
Published Data ◽  
Molecular Orbital Calculations ◽  
Good Prediction ◽  
Proton Chemical Shift ◽  
Screening Constant ◽  
Bond Lengths ◽  
Bond Indices

Protonations of isaxonine phosphate are studied by performing CNDO/2 and CNDO/S molecular orbital calculations. Results are compared with previously published data. Wiberg's bond indices and S character percentages calculated using electronic populations are shown to correctly predict variations of bond lengths and bond angles as well as [Formula: see text] coupling constants. A good prediction of proton chemical shift variations using a calculation of the screening constant was obtained.

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