Final answer:
The dihedral angle changes when there is rotation around the C-C bond, increasing or decreasing based on the direction of the rotation and the initial conformation of the molecule.
Step-by-step explanation:
In the scenario where the front carbon (C) rotates clockwise while the back carbon (C) is held stationary, the dihedral angle or torsion angle changes. The dihedral angle is defined as the angle between two planes defined by the atoms in the molecule. When the front C of a C-C bond rotates relative to the back C, new conformations are created, which have different dihedral angles. Therefore, when there is rotation around the C-C bond, the dihedral angle does not remain constant; it either increases or decreases depending on the direction of rotation and the original conformation. For example, rotation from a staggered conformation towards an eclipsed conformation will reduce the dihedral angle, whereas rotation from an eclipsed conformation back to a staggered one will increase it. Hence, as the C-C bonds rotate, the correct answer would be either B) The dihedral angle increases or C) The dihedral angle decreases, depending on the direction of the rotation and initial conformation.