### 抄録

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.

元の言語 | 英語 |
---|---|

ページ（範囲） | 5697-5701 |

ページ数 | 5 |

ジャーナル | Journal of physical chemistry |

巻 | 100 |

発行部数 | 14 |

出版物ステータス | 出版済み - 4 4 1996 |

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### All Science Journal Classification (ASJC) codes

- Engineering(all)
- Physical and Theoretical Chemistry

### これを引用

_{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.

研究成果: ジャーナルへの寄稿 › 記事

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

*Journal of physical chemistry*, 巻. 100, 番号 14, pp. 5697-5701.

_{6h}structures in large cyclic polyenes. Journal of physical chemistry. 1996 4 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.

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M3 - Article

VL - 100

SP - 5697

EP - 5701

JO - Journal of Physical Chemistry

JF - Journal of Physical Chemistry

SN - 0022-3654

IS - 14

ER -