Structures and numbering of hexamethylene-1,6-bis(N,N-dimethyl-N-dodecyl-ammonium bromide) (1), pentamethylene-1,5-bis(N,N-dimethyl-N-dodecylammonium bromide) (2), tetramethylene-1,4-bis(N,N-dimethyl-N-dodecylammonium bromide) (3), trimethylene-1,3-bis-N,N-dimethyl-N-dodecylammonium bromide) (4) and ethylene-1,2-bis(N,N-dimethyl-N-dodecylammonium bromide) (5).