The Minimum Estrada Index of Spiro Compounds with k Quadrangles

Document Type : Research Paper


Yazd University


Abstract. Let G = (V,E) be a fi nite and simple graph with λ1, λ2,...,λn as its eigenvalues.The Estrada index of G is EE(G) =∑ni=1e^{λi} . A spiro compound is a chemical compound that presents a twisted structure of two or more rings, in which 2 or 3 rings are linked together by one common atom. In this paper, we show that the symmetric and stable spiro compounds among all spiro compounds have the minimum Estrada index.


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