NMR SPECTROSCOPIC STUDIES OF INTERMEDIARY METABOLITES OF CYCLOPHOSPHAMIDE. A COMPREHENSIVE KINETIC ANALYSIS OF THE INTERCONVERSION OF CIS‐ AND TRANS‐4‐HYDROXYCYCLOPHOSPHAMIDE WITH ALDOPHOSPHAMIDE AND THE CONCOMITANT PARTITIONING OF ALDOPHOSPHAMIDE BETWEEN IRREVERSIBLE FRAGMENTATION AND REVERSIBLE CO