青にシフトした水素結合の物理的起源について

Xiaosong Li¹, Lei Liu, H Bernhard Schlegel

¹Contribution from the Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.

Journal of the American Chemical Society

|August 9, 2002

まとめ

水素結合は,ブルーシフト系における水素結合の伸縮周波数を驚くほど増加させることができる. 計算研究で観察されたこの現象は,主に電子相関ではなく,静電相互作用によって引き起こされます.

科学分野:

コンピューティング・ケミストリー
分子相互作用とは
スペクトロスコーピーは,スペクトロスコーピーを用います.

背景:

水素結合は,通常,複雑化時にX-H伸縮周波数の減少を伴う.
青にシフトした水素結合系は,X-H伸縮周波数の異常な増加を示している.

研究の目的:

水素結合系システムにおけるブルーシフト現象の原因となる根本的なメカニズムを調査する.
青いシフトの原因となる軌道相互作用と対比して静電相互作用の役割を決定する.

主な方法:

量子化学の計算は,理論の様々なレベルで行われました.
考案的なF(3) C·H··FH系と関連する分子が研究されました.
荷重再分配と分子間力に関する分析が行われました.

主要な成果:

青いシフトはハートリー・フォックレベルで再現され,電子相関が主な原因ではないことを示唆しています.
炭素中心や陽子ドナー上の単一のペアのないシステムでは,実質的なブルーシフトが観察されました.
軌道間相互作用は,X-H結合を延長し,ブルーシフトの観測と矛盾していることが判明しました.

結論:

水素結合におけるブルーシフトは,主に静電相互作用によって支配される.
均衡幾何学における分子断片間のパウリ反発は,X-H結合を圧縮し,青のシフトを引き起こします.
この排斥的相互作用は,これらの特定のシステムにおける結合延長軌道効果を覆す.

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