code: def spine_to_terminal_wedge(mol):
      
      for i, a in mol.atoms_iter():
          if mol.neighbor_count(i) == 1:
              ni, nb = list(mol.neighbors(i).items())[0]
              if nb.order == 1 and nb.type in (1, 2) \
                      and ni > i != nb.is_lower_first:
                  nb.is_lower_first = not nb.is_lower_first
                  nb.type = {1: 2, 2: 1}[nb.type]
docs: Arrange stereo wedge direction from spine to terminal atom