Physical Image vs. Structure Relation, Part 13¹: Calculational Evidences for the ^2hJ_PH Spin–Spin Coupling in Internally H-Bonded Isomers of Some 1-Oxoalkanephosphonate Hydrazones

Abstract

The P(IV)↔H spin–spin transfer across the N─H· · · O⁻−P⁺ intramolecular H-bond previously observed NMR spectroscopically for Z stereoisomers of hydrazones of O,O′ -diisopropyl 1-oxoalkanephosphonates, ^2h J _PH = 2.95 ± 0.35 Hz, was rationalized using Fermi-contact (FC) contributions to such J _PH couplings. Moreover, the FC terms were found to be dominant terms of these ^2h J _PH couplings. The applied FPT-DFT(B3LYP) FC calculational approach was successfully tested on J _PH couplings in model phosphorus esters. As a result, linear relation J _PH ^obsd (CDCl₃) vs. J ^FC _PH ^calcd was established for different long-range J _PH couplings occurring via an oxygen atom of the phosphoryl group.

Keywords:

• Conformations
• Fermi-contact term
• FPT-DFT method
• indirect ^2h J _PH coupling across intramolecular H-bond
• NMR spectroscopy
• phosphorus esters

Dedicated to Professor Marian Mikołajczyk from the CBMiM PAN in Łódź, Poland, on the occasion of his 70th birthday.

Notes

^a Absolute values experimentally measured^3,4 for both isomers in the E/Z mixture (excluding 1a)

^b spin perturbation placed on the H-bonded proton^4c

^cspin perturbation placed on the P nucleus^4c

^d predicted using Gaussian 03 (all four Ramsey's terms considered)

^e the FC term was found as identical with that FPT computed according to footnote ^b

^f estimated with the scaling relationship given in ref.^[20]

^g not detected; ^h not computed.