### Abstract

The geometrical and electronic structures of large cyclic polyenes, annulenes, with 18, 30, 42, 54, and 66 CH units, which belong to a subgroup of aromatic (4n + 2)π electron systems and can exhibit a delocalized D_{6h} geometry, are studied using the MNDOC (C for correlation) method coupled with a conventional perturbation treatment. The optimized D_{6h} structures have nearly equal C-C bond lengths of approximately 1.4 Å, in contrast to the D_{3h} ones which exhibit strong bond-length alternation. It is well-known that the Hartree-Fock-based self-consistent-field (SCF) methods generally prefer bond-alternation structures to bond-equalization ones. However, second-order energy (always minus) is larger in the D_{6h} structures, due to the small HOMO-LUMO gap in the D_{6h} structures with nearly equal C-C bond lengths. It is clarified that these two effects strongly compete in the structure of [18]- and [30]annulenes; in [18]annulehe the D_{6h} structure is 6.4 kcal/ mol more favorable, but in [30]annulene the D_{6h} structure is less stable by 4.6 kcal/mol. Moreover, in [42]-, [54]-, and [66]annulenes, the D_{3h} structures are clearly more stable than the corresponding D_{6h} ones.

Original language | English |
---|---|

Pages (from-to) | 5697-5701 |

Number of pages | 5 |

Journal | Journal of physical chemistry |

Volume | 100 |

Issue number | 14 |

Publication status | Published - Apr 4 1996 |

### Fingerprint

### All Science Journal Classification (ASJC) codes

- Engineering(all)
- Physical and Theoretical Chemistry

### Cite this

_{6h}structures in large cyclic polyenes.

*Journal of physical chemistry*,

*100*(14), 5697-5701.

**Electron correlation effects and possible D _{6h} structures in large cyclic polyenes.** / Yoshizawa, Kazunari; Kato, Takashi; Yamabe, Tokio.

Research output: Contribution to journal › Article

_{6h}structures in large cyclic polyenes',

*Journal of physical chemistry*, vol. 100, no. 14, pp. 5697-5701.

_{6h}structures in large cyclic polyenes. Journal of physical chemistry. 1996 Apr 4;100(14):5697-5701.

}

TY - JOUR

T1 - Electron correlation effects and possible D6h structures in large cyclic polyenes

AU - Yoshizawa, Kazunari

AU - Kato, Takashi

AU - Yamabe, Tokio

PY - 1996/4/4

Y1 - 1996/4/4

N2 - The geometrical and electronic structures of large cyclic polyenes, annulenes, with 18, 30, 42, 54, and 66 CH units, which belong to a subgroup of aromatic (4n + 2)π electron systems and can exhibit a delocalized D6h geometry, are studied using the MNDOC (C for correlation) method coupled with a conventional perturbation treatment. The optimized D6h structures have nearly equal C-C bond lengths of approximately 1.4 Å, in contrast to the D3h ones which exhibit strong bond-length alternation. It is well-known that the Hartree-Fock-based self-consistent-field (SCF) methods generally prefer bond-alternation structures to bond-equalization ones. However, second-order energy (always minus) is larger in the D6h structures, due to the small HOMO-LUMO gap in the D6h structures with nearly equal C-C bond lengths. It is clarified that these two effects strongly compete in the structure of [18]- and [30]annulenes; in [18]annulehe the D6h structure is 6.4 kcal/ mol more favorable, but in [30]annulene the D6h structure is less stable by 4.6 kcal/mol. Moreover, in [42]-, [54]-, and [66]annulenes, the D3h structures are clearly more stable than the corresponding D6h ones.

AB - The geometrical and electronic structures of large cyclic polyenes, annulenes, with 18, 30, 42, 54, and 66 CH units, which belong to a subgroup of aromatic (4n + 2)π electron systems and can exhibit a delocalized D6h geometry, are studied using the MNDOC (C for correlation) method coupled with a conventional perturbation treatment. The optimized D6h structures have nearly equal C-C bond lengths of approximately 1.4 Å, in contrast to the D3h ones which exhibit strong bond-length alternation. It is well-known that the Hartree-Fock-based self-consistent-field (SCF) methods generally prefer bond-alternation structures to bond-equalization ones. However, second-order energy (always minus) is larger in the D6h structures, due to the small HOMO-LUMO gap in the D6h structures with nearly equal C-C bond lengths. It is clarified that these two effects strongly compete in the structure of [18]- and [30]annulenes; in [18]annulehe the D6h structure is 6.4 kcal/ mol more favorable, but in [30]annulene the D6h structure is less stable by 4.6 kcal/mol. Moreover, in [42]-, [54]-, and [66]annulenes, the D3h structures are clearly more stable than the corresponding D6h ones.

UR - http://www.scopus.com/inward/record.url?scp=0030568445&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0030568445&partnerID=8YFLogxK

M3 - Article

VL - 100

SP - 5697

EP - 5701

JO - Journal of Physical Chemistry

JF - Journal of Physical Chemistry

SN - 0022-3654

IS - 14

ER -