Potential surfaces butane rotation

To conclude this computer project, we shall lirst search the potential surface for rotation of u-butane about its 23 C C bond, for which we think we know the answei, then seai ch the potential sutface foi I-butene, foi which we do not. In I -butene, the double bond establishes a rigid plane but the methyl group can take up several d i ffe ren t positions re I at i ve to i t by rotation ab ou t th e 2 - 3 s i n g I e bo n d,... 

The energy of the dihedral angles must be periodic, because, for example, dihedral angles across single bonds are free to rotate. This term s potential energy surface is the same as the butane central dihedral angle (Fig. 3.2) and is treated as a sum of cosine terms (Fig. 3.6) ... 

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