The eigenvalues λ i of an Hermitian matrix A of order n satisfy the inequality ∑ i = 1 n | λ i | ≤ n 1/2 N, where N is the Frobenius norm of A. Let n and ν be, respectively, the numbers of atoms and bonds in the conjugated system of a hydrocarbon, and let E be the corresponding Hückel matrix. Then the Hückel π‐electron energy is nα + εβ , where [2ν + n(n − 1)| det E | 2/n ] 1/2 ≤ ε ≤ (2nν) 1/2 . Analogous bounds are obtained for π‐electron energies calculated by Wheland's method. An approximation for the Hückel π‐electron delocalization energy (DE) in the closed‐shell ground state of a hydrocarbon is DE / β = an 1/2 − n + r , where a ≈ 1.30 , and r = 0 or 1 , according as n is even or odd.