Acyclic systems with extremal Hückel π-electron energy

The main result of the present work is the proof that among acyclic polyenes C_nH_n+2, the linear isomer H₂C=(CH)_n–2=CH₂ has maximal HMO -electron energy. The 1,1-divinyl isomer (H₂C=CH)₂C(CH)_n–6=CH₂ has maximal -energy among branched acyclic systems. Among trees withn vertices, the star has minimal energy. A number of additional inequalities for HMO total -electron energy of acyclic conjugated systems are proved.