Bond rotation, alkanes propane

Propane, the next higher member in the alkane series., also has a torsional barrier that results in hindered rotation around the carbon-carbon bonds. The barrier is slightly higher in propane than in ethane—a total of 14 kj/mol (3.4 kcal/mol) versus 12 kj/mol. 

Conformational isomerism in propane Propane is a three-carbon- (sp -hybridized) atom-containing linear alkane. All are tetrahedrally arranged. When a hydrogen atom of ethane is replaced by a methyl (CH3) group, we have propane. There is rotation about two C-C cr bonds. 

FIGURE 4.1 3D shapes of some alkanes using balls (for atoms) and sticks (for bonds) to depict (a) ethane, (b) propane, and (c) butane, (d) The dynamics of ethane as it rotates around the C—C bond and changes the relative orientations of the C—H bonds. The variable location of the distinctly colored H emphasizes the rotation. 

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