Eccentric Connectivity Index of Chemical Trees

The eccentric connectivity index $\xi^c$ is a distance--based molecular structure descriptor that was recently used for mathematical modeling of biological activities of diverse nature. We prove that the broom has maximum $\xi^c$ among trees with a fixed maximum vertex degree, and characterize such trees with minimum $\xi^c$\,. In addition, we propose a simple linear algorithm for calculating $\xi^c$ of trees.