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出典:『Wikipedia』 (2010/11/08 03:46 UTC 版)

英語による解説

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Pentane interference or syn-pentane interaction is the steric hindrance that the two terminal methyl groups experience in one of the chemical conformations of n-pentane. The possible conformations are combinations of anti conformations and gauche conformations and are anti-anti, anti-gauche⁺, gauche⁺ - gauche⁺ and gauche⁺ - gauche⁻ of which the last one is especially energetically unfavorable. In macromolecules such as polyethylene pentane interference occurs between every fifth carbon atom. This is not to be confused with the 1,3-diaxial interactions of cyclohexane derivatives (gauche interactions shared between substituents and the ring). A clear example of the syn-pentane interaction is apparent in the diaxial versus diequatorial heats of formation of cis 1,3-dialkyl cyclohexanes. Relative to the diequatorial conformer, the diaxial conformer is 2-3 kcal/mol higher in energy than the value that would be expected based on 1,3-diaxial interactions alone. Pentane interference helps explain molecular geometries in many chemical compounds, product ratios, and purported transition states. One specific type of syn-pentane interaction is known as 1,3 allylic strain or (A^1,3 strain).