Past exam of the chemistry B course of the University of Cambridge 2025 Paper 2 B9 b iii Solution 2026-10-20
Secondary amines normally favor non-geminal disubstitution, putting the second amino substituent on a different phosphorus. The first installed group donates electron density to the P–N framework and deactivates its own phosphorus toward further attack. It is also bulkier than an initially installed primary-amino group. Crucially, has no N–H proton, so the proton-abstraction/chloride-elimination pathway that can direct a primary amine geminally is unavailable. Direct attack at a less-deactivated site is favored. The resulting non-geminal products can have cis or trans relative orientations around the ring; non-geminal substitution alone does not select one of these stereoisomers. These are useful trends, with known substituent-dependent exceptions in experimentally characterized mixed derivatives.[ref]
Regiochemical Control in the Substitution Reactions of Cyclotriphosphazene Derivatives with Secondary Amines by Serap Beşli and others. 2018, abstract, pyrrolidine/dimethylamine substitution of differently substituted rings