Butane planar arrangement

The term conformation (Koenig, 1980) is used to describe the spatial arrangements of various atoms in a molecule that may occur because of rotations about single bonds. The planar cis and planar trans conformations of a n-butane molecule produced by rotations about the bond joining carbons 2 and 3 are illustrated in Fig. 

The most widely studied crystalline polymer is polyethylene. The lowest-energy chain conformation of this macromolecule can be evaluated from considerations of the conformations of the n-butane molecule (Fig. 3.5). A series of all trans bonds produce the lowest-energy conformation in n-butane because of steric interactions and this is reflected in polyethylene where the most stable molecular conformation is the crystal with all trans bonds, i.e. the planar zig-zag. These molecules then pack into the orthorhombic unit cell given in Table 4.1. The arrangement of the molecules in the polyethylene crystal structure is illustrated in Fig. 4.5 with the polymer molecules lying parallel to the c axis. The molecules are held... 

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