関連する実験動画
Updated: Jul 11, 2026
06:15
Interactive Molecular Model Assembly with 3D Printing
Published on: August 13, 2020
まとめ
エタンの内部回転バリアは,局所的または非局所的分子軌道を使用して説明することができます. 両方の方法は,化学システムにおけるこの障壁を引き起こす力について,異なるものの,有効な視点を提供します.
科学分野:
- コンピューティング・ケミストリー
- 量子化学とは,量子化学である.
- 分子スペクトロスコーピーは分子スペクトロスコーピーを用います.
背景:
- 分子の内部回転に対するエネルギー的障壁を理解することは,化学反応性や構成的好みを予測するために極めて重要です.
- エタンの内部回転障壁は,物理有機化学における基本的なモデルシステムとして機能する.
研究 の 目的:
- エタンの内部回転障壁について,質的かつ直感的に有用な説明を提供すること.
- 局所的および非局所的分子軌道を使用して,バリアの記述を比較および対比する.
主な方法:
- デロカライズされた分子軌道 (MOs) とローカライズされた分子軌道 (MOs) を用いた定性分析.
- ウッドワード・ホフマンとウォルシュの法則のような軌道制御概念の検討.
- ステリック相互作用と静電モデルの検討.
主要な成果:
- デロカライズされたMOsは,遮蔽された水素原子間の長距離抗結合相互作用によってバリアを説明します.
- 局所的なMOは,遮蔽された炭素-水素結合の間の破壊的な干渉に障壁を起因している.
- 剛性回転後の構造的緩和は,エネルギーへの影響は最小ですが,エネルギー再分配を引き起こします.
結論:
- デロカライズされた軌道とローカライズされた軌道の両方の記述は,エタンの回転障壁に対する妥当な説明を提供します.
- 軌道制御とステリック相互作用の区別は必ずしも正確ではない.
- 現在,局所的または非局所的軌道を用いた,現在の化学的思考に基づく説明が好まれている.
関連する概念動画
02:18Conformations of Ethane and Propane
In an organic molecule, free rotation about the carbon-carbon single bond results in energetically different conformers of the molecule. Due to this rotation, called the internal rotation, ethane has two major conformations — staggered and eclipsed.
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered ethane, the...
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered ethane, the...
02:20Conformations of Butane
Unlike ethane and propane that have only two major conformations, butane has more than two conformers. The staggered form of butane in which the bulky methyl groups on the two carbons are placed on opposite sides, that is, at a dihedral angle of 180°, is the lowest energy, most stable form — called the anti conformer. This conformation is stabilized due to the absence of steric repulsion between the largely spaced out methyl groups. The other two staggered conformations are degenerate and have...
02:29Conformations of Cycloalkanes
Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3 hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that was based on the...
02:11Conformations of Cyclohexane
Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
02:02Chair Conformation of Cyclohexane
The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
01:27The Molecular Nature of Internal Energy
The internal energy of a molecule is determined by its degrees of freedom, including translational, rotational, and vibrational motions. In addition to these kinetic activities, the energy of molecules is also shaped by electronic energy, intermolecular forces, and the rest-mass energy of electrons and nuclei. These factors collectively influence the energy state of the molecules. The equipartition theorem of classical mechanics provides insight into this energy distribution. It posits that the...