(b) Imagine that you could hold two atoms that are bonded together, twist them, and not change the bond length. Would it be easier to twist (rotate) around a single s bond or around a double 1s plus p2 bond, or would they be the same?

Video transcript

Hey everyone, we're given the following figure and were asked if it would be easier to rotate the central carbon carbon bonds in methane or ethane, comparing these two structures. We can see that we have a single bond and ethane, which means we have a sigma bond. Looking at the thin, we can see that we have a sigma plus a pi bond, and since a pi bond is formed by a parallel overlap of two P orbital's, it is impossible to rotate it without breaking it. So this double bond makes it difficult to rotate while a single bond can rotate freely due to the electron density about the inner nuclear axis. So our answer here is going to be methane is easier to rotate and this is due to the single bond between our two carbon atoms. So I hope that made sense. And let us know if you have any questions.