C=C,C=O,C=S の二重結合にメチル基を加えたときの運動学と熱力学の比較
David J Henry1, Michelle L Coote, Rodolfo Gómez-Balderas
1Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia. djhenry@rsc.anu.edu.au
Journal of the American Chemical Society
|February 12, 2004
まとめ
アルケーン,カルボニル,チオカルボニルへのメチルラジカル添加が研究されました. 反応障壁は,速度を理解する上で鍵となるものであり,加算はしばしば炭素センターを好む.
科学分野:
- コンピューティング・ケミストリー
- 化学動力学 化学動力学
- 反応メカニズム 反応メカニズム
背景:
- ラジカル添加反応を理解することは,化学合成と大気化学にとって極めて重要です.
- 以前の研究では,急進的な追加が調査されていますが,異なる不飽和システム全体にわたる包括的な分析が必要です.
研究 の 目的:
- アルケーン,カルボニル,チオカルボニルへのメチル基の添加の障壁,エンタルピー,速度定数を調査する.
- 逆ベータ分裂反応を分析する.
- 曲線交差モデルを使用して,発見を合理化する.
主な方法:
- 反応エネルギーと運動を決定するために,高レベルのアビニシオ計算が採用されました.
- 曲線交差モデルを使用して,観察された傾向を合理化しました.
- 分析には,加算およびβ分裂反応のバリア,エンタルピー,速度定数が含まれていました.
主要な成果:
- 添加反応は,初期の移行構造を通して進行します.
- C=C結合の場合,加法障壁は主に外熱性によって引き起こされ,非置換炭素を好む.
- C=O結合の場合,バリアはエクソ熱性およびシングレット・トリプレット・ギャップに依存し,炭素添加を好む.
- チオカルボニルの場合,炭素添加は熱力学的に好ましいが,硫黄添加はスピン密度による低 кинеティックバリアを有する.
結論:
- 反応速度は主に活性化バリアによって決定されるが,エントロピー差は小さい.
- 炭素中心への添加は,これらのシステム全体で一般的に動力学的に,熱力学的に好ましい.
- スピン密度は,チオカルボニルの反応経路を決定する上で重要な役割を果たします.
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