Biphenyl symmetry group dependence on torsional angle What is the symmetry group of the biphenyl when the torsional angle between the phenyls is 20 degrees? What about when it is 90 degrees?
The $20$ degree structure exhibits the $D_2$ point group and the $90$ degree $D_{2d}$.

The figure below shows an $D_{2d}$ structure (a spiropentadiene) but the similarity in symmetry should be clear (I hope ). (From molecule-viewer.com)



The biphenyl at an angle not $90$ degrees is shown below