In this paper, we report, for the first time, a plausible full reaction pathway for the activation of O-2 by a tetraazamacrocyclic monocopper(I) complex and for the subsequent intramolecular alkylic hydroxylation to yield the alkoxide product. This theoretical insight offers remarkable support to the fundamental hypothesis in the field that a hydroperoxo complex of the type (CuOOH)-O-II intermediate is the key intermediate in this class of reactions. Overall, we give insight into an intramolecular alkylic C-H bond activation due to the O-2 binding to copper(I) with an end-on eta(1)-O-2 ligation. The loss of a water molecule involves the final substrate oxygenation. The complex we consider is a biomimetic of several systems of biological relevance, such as amine oxidases, peptidylglycine-alpha-hydroxylating monooxygenase, and dopamine-beta monooxygenases.