03_01_ of alkanes and cycloalkanes html

1、Chapter 3 Conformations of Alkanes andCycloalkanes3.1Conformational Analysis of EthaneConformations are different spatial arrangements of a molecule that are generated by rotation about single bonds.eclipsed conformationEthaneeclipsed conformationEthanestaggered conformationEthanestaggered conformat

2、ionEthaneHHHHHHHHHHHHNewmanSawhorseProjection Formulas of the Staggered Conformation of EthaneHHHHHH180HHHHHHTwo bonds are anti when the angle between them is 180.Anti RelationshipsH60HHHHHHHHHHHTwo bonds are gauche when the angle between them is 180.Gauche RelationshipsThe terms anti and gauche app

3、ly only to bonds (or groups) on adjacent carbons, and only to staggered conformations.An important point:12 kJ/mol060120180240300The eclipsed conformation of ethane is 12 kJ/mol less stable than the staggered.The eclipsed conformation is destabilized by torsional strain.Torsional strain is the desta

4、bilization that results from eclipsed bonds.Torsional strain3.2Conformational Analysis of Butane14 kJ/mol3 kJ/mol060120180240300van der Waals strainThe gauche conformation of butane is 3 kJ/mol less stable than the anti.The gauche conformation is destabilized by van der Waals strain (also called ste

5、ric strain).van der Waals strain is the destabilization that results from atoms being too close together.van der Waals strainThe conformation of butane in which the two methyl groups are eclipsed with each other is is the least stable of all the conformations.It is destabilized by both torsional strain (eclipsed bonds) and van der Waals strain.3.3Conformational Analysis of Higher AlkanesHexaneThe most stable confor