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Ring Currents in Condensed Ring Systems

Anusooya, Y and Chakrabarti, Aparna and Pati, Swapan K and Ramasesha, S (1998) Ring Currents in Condensed Ring Systems. In: International Journal of Quantum Chemistry, 70 (3). pp. 503-513.

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We have studied magnetism and aromaticity of polycyclic ring systems by analyzing ring currents for different circulations in these molecules. The technique employed for calculating ring currents uses correction vectors which implicitly includes all the eigenstates of the Hamiltonian in the space of the chosen configurations. We have employed the Pariser-Parr-Pople Hamiltonian and have carried out full configuration interaction CI calculations for small systems and approximate CI calculations for large systems. The systems studied include polyacenes, nonaromatic ring systems including the $C_6_0$ fragments pyracylene, fluoranthene, and corannulene, and heteroatomic systems with upto two six-membered rings. We find that in polyacenes, the aromaticity of the extreme phenyl rings reduces with increasing number of phenyl rings in the system, and it saturates at approx 2/3 the benzene value. In systems containing nonaromatic rings, we find paramagnetic or diamagnetic behavior for different circulations depending upon the number of atoms in the chosen ring cycle, in agreement with the 4n + 2 rule. In corannulene, the largest fragment of $C_6_0$ we have studied, the five-membered ring is weakly diamagnetic while the six-membered ring is more diamagnetic, although much less than in isolated benzene. The ring structures with heteroatoms studied are pyridine, pyrimidine, and its isomers, s-triazine, quinoline and its isomer, and quinazoline and its isomers. All these have similar ring currents as in their purely carbon counterparts, although ions of these molecules show interesting behavior.

Item Type: Journal Article
Publication: International Journal of Quantum Chemistry
Publisher: John Wiley & Sons, Inc.
Additional Information: The copyright belongs to John Wiley & Sons, Inc.
Keywords: Ring currents;Conjugated molecules;Pariser parr pople model;Valence bond method;Correction vector technique
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited: 14 Jun 2006
Last Modified: 19 Sep 2010 04:29
URI: http://eprints.iisc.ac.in/id/eprint/7634

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