Eclipsed state

A further feature of three-membered rings is that they must be planar, and a consequence of this is that, in cyclopropane, all C-H bonds are in the high-energy eclipsed state. There can be no conformational mobility to overcome this. 

If cyciobutane were planar, all C-H bonds would be in the high-energy eclipsed state. It transpires that cyciobutane is not planar, since it can adopt a... 

This reaction is conducted in a solvent that won t separate the ion pairs. This necessitates an eclipsed / syn orientation for elimination to take place. If there is a choice of eclipsed states, elimination will take place during the most stable, which generally gives the less substituted alkene. 

Figure 2.2 Newman and saw horse projections for n-butane. (a) A staggered state (planar trans) with angle of bond rotation (j> = 0 and (b) an eclipsed state (planar cis) with = 180°.

Calculate the smallest separations between hydrogen atoms connected to the two different carbon atoms 2 and 3 of the butane molecule when the central C—C bond, between atoms 2 and 3, is in the trans, gauche and eclipsed states. 

Rotation through syn state Libration through perfectly staggered state Rotation through eclipsed state Libration through the anti conformation Rotation between gauche conformations Rotation between gauche and anti conformations... 

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