So peptide bonds are resonance stabilized, which means they have a double bond character. Now what do we mean by double bond character? Well, basically the length between this carbon and this nitrogen will be somewhere in between a single bond and a double bond. Now remember from organic chemistry that single bonds can actually rotate, but double bonds cannot rotate. And because we have a double bond character between the carbon and the nitrogen, this peptide bond also will not be able to rotate in space. So this bond, this bond, this bond and this bond, the atoms that are connected by these bonds will not be able to rotate in space.