- 3 Apr, RE: Torsional Strain (Scheme 12) - So does the "strain" arise from the electrostatic repulsion of the two filled sp3 orbitals in the probability density part of the orbitals pointing directly at each other i.e. the black parts? Or is it the whole orbital? Confusing with the arrows pointing at the part of the orbital overlapping with the bound hydrogens. Probably not important. I assume the "torsional" part comes from the unfavourable interaction while the bond is spinning. Kind of like trying to turning a tap when there's not enough space for the tap to move. MHT - Yes, that's a nice analogy. Yes, the repulsion is from the electrons in the whole orbital. The orbital arises, for example, from a contributing hydrogen s and a carbon sp3. Once there is a bond formed, we kind of stop thinking about the separate lobes because the electrons are free to move throughout the bond. The largest torsional strain is when the bonds are eclipsed. So there's always strain, just more or less depending on the relative positions.