関連する実験動画
Updated: May 9, 2026
09:48
Original Experimental Approach for Assessing Transport Fuel Stability
Published on: October 21, 2016
アルケンの相対的安定性に対する相関効果
William C McKee1, Paul von Ragué Schleyer
1Center for Computational Chemistry and Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.
Journal of the American Chemical Society
|August 6, 2013
まとめ
高分岐アルカンと"原分岐"を持つアルカンは,電子相関効果によりより安定しています. これらの効果は,特に1,3-アルキル群の間では,アルカンの安定性と相関エネルギーを強化します.
科学分野:
- コンピューティング・ケミストリー
- 有機化学 オーガニック・ケミストリー
- 物理化学 物理化学
背景:
- アルカン分岐効果は,その線形同位体 (例えばn-ブタン) と比較して,分岐アルカン (例えば,イソブタン) の安定性の増加を記述する.
- 線形アルケンは線形アルケンを表しています.
- プロトブランチ
- これらは1,3-アルキル-アルキル相互作用で,より低いエネルギーに寄与します.
研究 の 目的:
- 枝分かれしたアルカンと原枝分かれしたアルカンにおける安定化エネルギーの起源を調査する.
- アルカンの安定性における電子相関の役割を明らかにする.
主な方法:
- プロトブランクアルカンとエタンのイソデズミック比較.
- 自相一致後のフィールド処理 (SCF) を利用した正確な初期計算.
- 局所化分子軌道二次モーラー-プレセット (LMO-MP2) の相関エネルギーの分割.
主要な成果:
- 枝分かれと原枝分かれは,アルケンの有意な安定エネルギーにつながります.
- 中距離の電子相関 (1.5-3.0 Å) は,安定性を正確に特徴づけるために重要である.
- LMO-MP2の分析により,1,3-アルキル群間の電子相関が安定性の向上の主な要因であることが明らかになった.
結論:
- 電子相関効果,特に1,3-アルキル相互作用の内では,枝分かれおよび原枝分かれアルケンの安定性の強化に起因する.
- これらの微妙な安定効果を捉えるには,正確な量子化学的方法が必要です.
関連する概念動画
01:59Relative Stabilities of Alkenes
The relative stability of alkenes can be determined by comparing their heats of hydrogenation. The lower heat of hydrogenation indicates the more stable alkene. The three main factors determining the relative stability of alkenes are i) the number of substituents attached to the double-bond carbon atoms, ii) hyperconjugation, and iii) the stereochemistry of the double bond.
02:14Combustion Energy: A Measure of Stability in Alkanes and Cycloalkanes
The low reactivity in alkanes can be attributed to the non-polar nature of C–C and C–H σ bonds. Alkanes, therefore, were initially termed as “paraffins,” derived from the Latin words: parum, meaning “too little,” and affinis, meaning “affinity.”
Alkanes undergo combustion in the presence of excess oxygen and high-temperature conditions to give carbon dioxide and water. A combustion reaction is the energy source in natural gas, liquified petroleum gas (LPG), fuel oil, gasoline, diesel fuel, and...
Alkanes undergo combustion in the presence of excess oxygen and high-temperature conditions to give carbon dioxide and water. A combustion reaction is the energy source in natural gas, liquified petroleum gas (LPG), fuel oil, gasoline, diesel fuel, and...
02:33Physical Properties of Alkanes
Alkanes are nonpolar molecules due to the presence of only carbon and hydrogen atoms. The electronegativity difference between carbon and hydrogen is minimal, and hence alkanes have a zero dipole moment. This leads to the presence of only dispersion forces between the molecules. The strength of dispersion forces is dependent on the surface area of the molecules on which they act. Since the surface area increases with the molecular length for straight-chain alkanes, the dispersion forces also...
02:42Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
02:47Structure and Bonding of Alkenes
Olefins, which are unsaturated hydrocarbons containing one or more carbon–carbon double bonds, are broadly divided into alkenes and cycloalkenes. The general chemical formula of an alkene is CnH2n.
Doubly bonded carbons are sp2 hybridized and have a trigonal planar geometry. The double bond is composed of a σ bond formed by the overlap of hybrid orbitals and a π bond produced by the lateral overlap of unhybridized 2p orbitals on both the carbons. Each carbon atom is bonded to two hydrogen atoms...
Doubly bonded carbons are sp2 hybridized and have a trigonal planar geometry. The double bond is composed of a σ bond formed by the overlap of hybrid orbitals and a π bond produced by the lateral overlap of unhybridized 2p orbitals on both the carbons. Each carbon atom is bonded to two hydrogen atoms...
02:18Constitutional Isomers of Alkanes
Organic compounds of the same molecular formula can have different structural formulas called constitutional isomers, and the phenomenon is known as constitutional isomerism. Alkanes with four or more carbons showing multiple structures with the same molecular formula thereby exhibit constitutional isomerism.
The linear isomer of an alkane is prefixed by the term “n”; hence a linear isomer of pentane is known as n-pentane. Based on the type of branching, some of the branched isomers are given...
The linear isomer of an alkane is prefixed by the term “n”; hence a linear isomer of pentane is known as n-pentane. Based on the type of branching, some of the branched isomers are given...