molec4 conformers by CAM-B3LYP-D3p3p:
 conformer    dihedral   E
                  deg   meV
     trans                0
 g   gauche   d0  296    23
 g1  gauche   d1  296    25
 s   saddle   d0  240   126
 sH  saddle   dH  180   126
 c   cis      d0    0   232
 h   hairpin            102

*Dihedrals: d0=[7,10,13,16], d1=[1,4,7,10], dH=[25,1,4,7]

Detailed analysis of chain-length dependence of hairpin vs trans conformer energies is given in Refs.[Byrd14,Zhugayevych18]