Ring currents in furan and thiophen

Abraham, Raymond J.; Sheppard, R. C.; Thomas, W. A.; Turner, Stephen

doi:10.1039/c19650000043

Cited by 12 publications

(16 citation statements)

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“…et Cyran8 ski al.16 suggested that the aromatic pathway of porphins includes the 18p- [16]annulene internal cross. If only the 18p- [16]annulene internal cross current path were present, the whole area outside the current path in the molecular plane should be deshielded. This would imply that all the centers of the pyrrolic rings outside the current loop have negative shieldings at the ring centers (NICS values).…”

Section: A Porphinsmentioning

confidence: 99%

“…This would imply that all the centers of the pyrrolic rings outside the current loop have negative shieldings at the ring centers (NICS values). Since this is not the case, it is unlikely that the 18p- [16]annulene internal cross is of importance for porphins.…”

Section: A Porphinsmentioning

confidence: 99%

“…The present study indi-cates that the aromatic pathway of porphins must be considered to be a superposition of several (4n ] 2)p paths, of which the dominating contributions are the 22p-and 26pelectron paths. The 18p- [16]annulene internal cross pathway, the traditional 18p- [18]annulene pathway, the most important 22p-electron pathway and the 26p-electron aromatic pathway for are sketched in Fig. 8.…”

Section: A Porphinsmentioning

confidence: 99%

“…1 Since porphyrins consist of four pyrrole units connected by conjugated bonds to form a larger ring, there are several possible routes for the induced ring current. Traditionally, porphyrins have been considered as a bridged 18p- [18]annulene with the inner NH groups acting as inert bridges.2h5 Recently, et al6 studied the aromatic pathway of Cyran8 ski free-base porphin and concluded that the aromatic pathway of porphins also includes the 18p- [16]annulene internal cross. The 18p- [16]annulene internal cross picture of the porphin molecule implies that the groups of the pyrrolic rings C 2 H 2 function only as exocylic bridges.…”

Section: Introductionmentioning

confidence: 99%

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The aromatic pathways of porphins, chlorins and bacteriochlorins

Jusélius

Sundholm

2000

Phys. Chem. Chem. Phys.

113

115

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The aromatic pathways of free-base porphins, chlorins and bacteriochlorins have been studied by calculating the nuclear magnetic shieldings at selected points outside the molecules. The strengths of the induced ring currents for a given magnetic Ðeld have been obtained by using the aromatic ring current shieldings (ARCS) method. We found that pyrrolic rings with an inner hydrogen have a local ring current of the same magnitude as the ring current for the pyrrole molecule. The local ring current for pyrrolic rings without an inner hydrogen is between half and one fourth of the pyrrole value depending on the porphyrin. The units of C 2 H 2 the pyrrolic rings in free-base porphin have recently been suggested to function as exocyclic bridges, but the present study indicates that this is not the case. The suggested 18p-[16]annulene inner cross aromatic pathway does not exist until all pyrrolic rings are saturated in the b-positions. Free-base trans-porphin was found to have the largest ring-current susceptibility among the molecules studied. Porphyrins for which the aromatic pathway has to pass the nitrogen of a pyrrolic unit with an inner hydrogen have signiÐcantly smaller ring currents than free-base trans-porphin. We also show that the 1H NMR shielding of the inner hydrogens is a sensitive measure of the strength of the ring current for the studied molecules.

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Section: A Porphinsmentioning

confidence: 99%

Section: A Porphinsmentioning

confidence: 99%

Section: A Porphinsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The aromatic pathways of porphins, chlorins and bacteriochlorins

Jusélius

Sundholm

2000

Phys. Chem. Chem. Phys.

113

115

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“…By comparison in 9 in which the carbomethoxy groups are necessarily adjacent to an aromatic ring the line position was 3.69 6, which allows the assignment of ester methyl groups in 8 as 3.65 (4-ester) and 3.28-3.38 6 (3-ester). It has been demonstrated that the ring current in thiophen does not differ significantly from that in benzene despite the observed differences in resonance energy (5).…”

Section: (A) Acetylenic Dipolarophilesmentioning

confidence: 99%

1,3-Dipolar cycloaddition reactions of 2-(2′-thienyl)aziridines

Lown¹,

Matsumoto²

1970

Can. J. Chem.

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The 1,3-dipolar cycloaddition of 2-(2'-thieny1)aziridines to a series of acetylenic and heterornultiple dipolarophiles leading to a series of new linked heterocycles is described. The versatility of these reactions suggests a general synthetic route to linked heterocycles.Canadian Journal of Chemistry, 48, 3399 (1970) We have recently described the preparation of the hitherto unknown 2-(2'-thieny1)aziridines (1) and have shown that, despite the lower resonance energy of the thiophene ring (20 kcal mole-' (2)) compared with benzene, 2-(2'-thieny1)-3-aroylaziridines undergo thermal cleavage of the 2-3 bond of the aziridine ring to azomethine u ylides at moderate temperatures. The transient dipoles could be trapped with olefinic dipolarophiles affording 2-(2'-thieny1)pyrrolidines.We report the examination of 1,3-dipolar cycloadditions of 2-(2'-thieny1)aziridines to acetylenic and heteromultiple bonds as a first approach to a general synthesis of linked heterocycles. (a) Acetylenic DipolarophilesBoth cis-and trans-3-benzoyl-l-cyclohexyl-2-(2'-thieny1)aziridine (1) reacted with dimethyl ~6~1 1 3 yl-3-deutero-2-(2'-thieny1)aziridine (91 % deuterium incorporation) gave 5 in which both branches of the 12 Hz AB quartet due to the methine protons were diminished to an equal extent (20 %). This discounts the trans-3-pyrroline structure 4 for the compound (which is in any case unlikely in view of the magnitude of the methine coupling) which would be expected to show one branch of the AB quartet diminished I C6Hll

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Physical Properties of Thiophene Derivatives

Gronowitz

Hörnfeldt

1991

Chemistry of Heterocyclic Compounds: A Series of Monographs

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Ring currents in furan and thiophen

Cited by 12 publications

References 0 publications

The aromatic pathways of porphins, chlorins and bacteriochlorins

The aromatic pathways of porphins, chlorins and bacteriochlorins

1,3-Dipolar cycloaddition reactions of 2-(2′-thienyl)aziridines

Physical Properties of Thiophene Derivatives

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