Obtaining Relative Induced Ring Currents Quantitatively from NICS

Stanger, Amnon

doi:10.1021/jo1000753

Cited by 169 publications

(149 citation statements)

References 40 publications

Supporting

Mentioning

143

Contrasting

Unclassified

Order By: Relevance

“…We added two hydrogens to the 1,4-positions of one benzene ring 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 1a ( Figure S13 To understand the mechanism for the formation of a diatropic interior in [n]CPP, we performed a NMR calculation on benzene molecules. Eight benzene molecules are placed on a circle with a diameter of 20 Å ( Figure S11).…”

Section: Resultsmentioning

confidence: 99%

Tetracyclo(2,7-carbazole)s: Diatropicity and Paratropicity of Inner Regions of Nanohoops

et al. 2016

View full text Add to dashboard Cite

Three N-substituted tetracyclo(2,7-carbazole)s were synthesized to investigate the inner regions of nanohoops. One compound has a 5,5-dimethylnonane bridge between two neighboring anti-carbazoles, which can be used as covalently bonded "methane probes". These probes near the ring center are strongly shielded by local ring currents and exhibit a singlet at δ = -2.70 ppm in (1)H NMR. To visualize local and macrocyclic ring currents separately, we drew nucleus-independent chemical shift contour maps of tetracyclo(9-methyl-2,7-carbazole) and [n]cycloparaphenylenes (CPPs). Local ring currents make the interior diatropic, and paratropic regions exist only outside the ring. Macrocyclic ring currents in [5]CPP to [7]CPP generate deshielding cones, which are typical of antiaromatic [4n]annulenes.

show abstract

Section: Resultsmentioning

confidence: 99%

Tetracyclo(2,7-carbazole)s: Diatropicity and Paratropicity of Inner Regions of Nanohoops

et al. 2016

View full text Add to dashboard Cite

show abstract

“…The scans were performed at the (U)B3LYP/6‐311+G(d,p) level of theory, 1.7 Å above the rings. The obtained data include only the π‐electron contribution to the out‐of‐plane component of the magnetic shielding tensor and were calculated by using the σ‐only model of the Aroma 1.0 program package…”

Section: Computational Detailsmentioning

confidence: 99%

A DFT Study of the Modulation of the Antiaromatic and Open‐Shell Character of Dibenzo[a,f]pentalene by Employing Three Strategies: Additional Benzoannulation, BN/CC Isosterism, and Substitution

Baranac‐Stojanović

2019

Chemistry A European J

View full text Add to dashboard Cite

Dibenzo[a,f]pentalene ([a,f]DBP) is a highly antiaromatic molecule having appreciable open‐shell singlet character in its ground state. In this work, DFT calculations at the B3LYP/6‐311+G(d,p) level of theory were performed to explore the efficiency of three strategies, that is, BN/CC isosterism, substitution, and (di)benzoannulation of [a,f]DBP, in controlling its electronic state and (anti)aromaticity. To evaluate the type and extent of the latter, the harmonic oscillator model of aromaticity (HOMA) and aromatic fluctuation (FLU) indices were used, along with the nucleus‐independent chemical shift NICS‐XY‐scan procedure. The results suggest that all three strategies could be employed to produce either the closed‐shell system or open‐shell species, which may be in the singlet or triplet ground state. Triplet states have been characterized as aromatic, which is in accordance with Baird's rule. All the singlet states were found to have weaker global paratropicity than [a,f]DBP. Additional (di)benzo fusion adds local aromatic subunit(s) and mainly retains the topology of the paratropic ring currents of the basic molecule. The substitution of two carbon atoms by the isoelectronic BN pair, or the introduction of substituents, results either in the same type and very similar topology of ring currents as in the parent compound, or leads to (anti)aromatic and nonaromatic subunits. The triplet states of all the examined compounds are also discussed.

show abstract

“…Positive values approaching 1.0 correspond to aromatic compounds, negative values to antiaromatic compounds, and values close to zero indicate nonaromatic compounds. Nucleus independent chemical shift (NICS) scans along an axis perpendicular (z-axis) to the ring planes were generated with the Aroma package 1.0 [71][72][73], using the Gauge-Independent Atomic Orbital (GIAO) method [74] at the GIAO-(U)B3LYP/6-311+G(d,p)//(U)B3LYP/6-311G(d,p) level. Scans were performed starting at the centre of the annulene to 5.0 Å above the ring plane with increments of 0.1 Å.…”

Section: Methodsmentioning

confidence: 99%

The Silacyclobutene Ring: An Indicator of Triplet State Baird-Aromaticity

2017

View full text Add to dashboard Cite

Baird's rule tells that the electron counts for aromaticity and antiaromaticity in the first ππ* triplet and singlet excited states (T 1 and S 1 ) are opposite to those in the ground state (S 0 ). Our hypothesis is that a silacyclobutene (SCB) ring fused with a [4n]annulene will remain closed in the T 1 state so as to retain T 1 aromaticity of the annulene while it will ring-open when fused to a [4n + 2]annulene in order to alleviate T 1 antiaromaticity. This feature should allow the SCB ring to function as an indicator for triplet state aromaticity. Quantum chemical calculations of energy and (anti)aromaticity changes along the reaction paths in the T 1 state support our hypothesis. The SCB ring should indicate T 1 aromaticity of [4n]annulenes by being photoinert except when fused to cyclobutadiene, where it ring-opens due to ring-strain relief.

show abstract

Obtaining Relative Induced Ring Currents Quantitatively from NICS

Cited by 169 publications

References 40 publications

Tetracyclo(2,7-carbazole)s: Diatropicity and Paratropicity of Inner Regions of Nanohoops

Tetracyclo(2,7-carbazole)s: Diatropicity and Paratropicity of Inner Regions of Nanohoops

A DFT Study of the Modulation of the Antiaromatic and Open‐Shell Character of Dibenzo[a,f]pentalene by Employing Three Strategies: Additional Benzoannulation, BN/CC Isosterism, and Substitution

The Silacyclobutene Ring: An Indicator of Triplet State Baird-Aromaticity

Contact Info

Product

Resources

About