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Conformation analysis of some novel isomeric phosphate esters by phosphorus nuclear magnetic resonance spectroscopy. Malcolm , Robert Bennet


A series of isomeric, six-membered, cyclic phenyl phosphate esters has been obtained by column chromatography of the mixtures of isomers obtained by reaction of phenyl phosphorodichloridate with appropriate 1,3-diols. The conformational analysis of the isomers was undertaken using both ¹ʜ and ³¹p n.m.r.. The basic conformation of the 2 oxo-2-phenoxy-1,3,2-dioxaphosphorinane ring system is that of a "flattened-chair". The thermodynamic free energy difference between "chair" conformations is sufficiently large for the basic ring to exist essentially in one favoured conformation, rationalized to have an axial phenoxy substituent. The stereospecific nature of Jpoch has been confirmed by using ¹ʜ n.m.r. to determine conformations. Long-range, ⁴J, ³¹p- ¹ʜ coupling constants have been found to be stereospecific in nature and useful in facilitating assignment of conformations for methyl-substituted-2-oxo-2-phenoxy-l,3,2-dioxaphosphorinanes. Similar ring systems having different substituents at phosphorus have been studied and the conformations of these derivatives are seen to differ depending on the nature of the phosphorus substituent. The conformation of a cyclic nucleotide has been determined from its ³¹p n.m.r. spectrum. The use of computer programming techniques and hetero-nuclear double resonance techniques, greatly facilitated the analysis of the n.m.r. spectra discussed. An interesting deceptively-simple type of ABX n.m.r. spectrum has been found for many of these cyclic phosphate derivatives and the explicit analysis of this system is presented.

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