Calculations: Cytochrome P450 enzymes facilitate a number of chemically different reactions. For example, amines can be either N-dealkylated or N-oxidized, but it is complex to rationalize which of these competing reactions occurs. It is shown that the barrier for inversion of the alkylamine nitrogen atom seems to be of vital importance for the amount of N-oxidized product formed relative to dealkylation and hydroxylation products.