Reply to Hengge: On the 31P chemical shifts of the phosphorane compounds

In reply to the letter from Hengge (ref. 1; see also references therein), our goal is to specify that the 31P chemical shifts (δP) of the phosphorane compounds P(OR)5 and PR5 are distributed in the broad range between −5 and −130 ppm (Fig. 1, p. 3 in ref. 2), depending on the chemical nature of the substituents. Hengge (1) refers to the phosphoranes substituted with aromatic groups, which have δP values between −55 and −85 ppm. Apparently, the aromatic rings influence the magnetic properties of the phosphorus nucleus. ATP triphosphate does not contain aromatic groups. Instead, we have a lysyl-substituted phosphorane (3), which rather resembles the phosphorane 4 (Fig. 1). Phosphate-atrane 3 may represent a model substrate composition for the nucleotidyl transfer 1→2 catalyzed by DNA ligase. During the intramolecular N→P nucleophilic attack in 3, the pentacoordinated phosphorane 4 is formed with δP = −13.7 ppm (p. 67 in ref. 2). The latter is shifted upfield by 2 ppm compared with δαP in 2. This relatively minor chemical shift difference may originate from the positive charge on the nitrogen atom, which additionally polarizes the P–N bond in 4.