如何由haworth式构象转变为船式构象
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发布时间：2022-04-29 21:44
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热心网友
时间：2022-06-23 13:50
根据现代分子结构理论,由于基团的相互作用
的缘故,椅式构象比船式构象稳定得多,常温下环己烷几乎完全是椅式构象.
通过船式构象的纽曼投影式（图2）,
可以看到碳原子1、2、4、5上相连的氢原子都处在全重叠式的位置上.从船式构象的透视式可以看到碳原子3和6（或称船头和船尾碳原子）上的两个向环内伸展的氢原子相距较近.上述两种情况都使氢原子之间产生较大的斥力,从而产生一种使船式构象扭转为椅式构象的内在力量,这种力称为扭转张力.这是船式构象不稳定的根本原因.在椅式构象中,组成碳环的任何相邻的两个碳原子上的氢,彼此都处在交叉式的位置上（图3）,
它们之间无扭转张力,比较稳定.
英文版解释：
Conformation[edit]
Main article: Cyclohexane conformation
The 6-vertexed ring does not conform to the shape of a perfect hexagon.The conformation of a flat 2D planar hexagon has considerable angle strain because its bonds are not 109.5 degrees; the torsional strain would also be considerable because all of the bonds would be eclipsed bonds.Therefore,to rece torsional strain,cyclohexane adopts a three-dimensional structure known as the chair conformation.There are also two other intermediate conformers; half chair,which is the most unstable conformer,and twist boat,which is more stable than the boat conformer.This was first proposed as early as 1890 by Hermann Sachse,but only gained widespread acceptance much later.The new conformation puts the carbons at an angle of 109.5°.Half of the hydrogens are in the plane of the ring (equatorial) while the other half are perpendicular to the plane (axial).This conformation allows for the most stable structure of cyclohexane.Another conformation of cyclohexane exists,known as boat conformation,but it interconverts to the slightly more stable chair formation.If cyclohexane is mono-substituted with a large substituent,then the substituent will most likely be found attached in an equatorial position,as this is the slightly more stable conformation.
Cyclohexane has the lowest angle and torsional strain of all the cycloalkanes,as a result cyclohexane has been deemed a 0 in total ring strain,a combination of angle and torsional strain.This also makes cyclohexane the most stable of the cycloalkanes and therefore will proce the least amount of heat (per CH2 unit) when burned compared to the other cycloalkanes.
