A Non-Karplus Effect: Evidence from Phosphorus Heterocycles and DFT Calculations of the Dependence of Vicinal Phosphorus–Hydrogen NMR Coupling Constants on Lone-Pair Conformation

Abstract

In contrast to literature reports of a Karplus-type curve that correlates 3JPH with phosphorus-hydrogen dihedral angle, a recently-reported glycine-derived 1,3,2-oxazaphospholidine (7c) has two hydrogen atoms on the ring with identical PNCH dihedral angles but measured coupling constants of ~6 Hz and 1.5 Hz. DFT calculations were in accord with these values, and suggested that the smaller coupling constant is negative. Experimental evidence of the opposite signs of these coupling constants was obtained by analysis of the ABX NMR spectrum of the new glycine-derived N-p-toluenesulfonyl phosphorus heterocycle 6c. DFT calculations on 6c and on Me2NPCl2 and t-BuPCl2 were also in accord with NMR data, and allowed confirmation of unusual features including a lone pair effect on 3JPH, the negative coupling constant, temperature-dependent chemical shifts due to rotation about the sulfonamide S-N bond, and vicinal phosphorus-hydrogen coupling constants over 40 Hz. Calculation of phosphorus-hydrogen coupling constants both as a function of PYCH dihedral angle θ(Y = O, N, C) and lone pair-PYC dihedral angle ω showed similar θ,ω surfaces for 3JPH with a range of 3JPH from −4.4 Hz to +51 Hz, and demonstrates the large non–Karplus effect of lone-pair conformation on vicinal phosphorus-hydrogen coupling constants.

Selective Derivatization of a Hexaphosphane from Functionalization of White Phosphorus

“…The larger one is found for the upward orientation (Et 3 P 9 : 81.6 Hz; t Bu 3 P 9 : 93.2 Hz), which strongly supports our assumption. The 3 J (PH) cannot be used for indication as both orientations are expected to have high values …”

“…The 3 J(PH) cannot be used for indication as both orientations are expected to have high values. 58 Crystallographic Investigation. Crystals of exo,endo-8 and exo,endo-9 were obtained by vapor diffusion of n-pentane into a dichloromethane or benzene solution of a mixture of exo,endo-8 and endo,endo-8 or exo,endo-9 and endo,endo-9, respectively.…”

First example of a high-level correlated calculation of the indirect spin–spin coupling constants involving tellurium: tellurophene and divinyl telluride

“…The same effect was also reported for the 3 J(P,H) and 3 J(Se,H) couplings due to the orientational lone pair effect of phosphorous and selenium. 71,72 Thus, it follows that geminal and vicinal 125 Te-1 H coupling constants show marked stereospecificity originating in the orientational lone pair effect of tellurium, in line with the same effects observed for phosphorous 71,74,75 and selenium, 56,72,73,[76][77][78][79][80][81] which is of prime importance for the stereochemical studies of organotellurium compounds.…”

Synthesis of dinucleoside acylphosphonites by phosphonodiamidite chemistry and investigation of phosphorus epimerization

“…The signal was observed as a doublet with 1 J PC = 22.4 Hz, in poor agreement with the calculated value of −60 Hz, although both CH 3 calculations were in remarkably good agreement ( 13 C: 31 ppm, 2 J PC = 54 Hz). Investigation of the poor agreement with the one-bond coupling constant has not been attempted, but the cause might be a phosphorus lone pair/carbonyl dihedral angle effect in which the true minimum energy conformation has not been found [ 48 – 50 ]. Once purified, 7 exhibited a strong carbonyl peak in the infrared spectrum at 1654 cm −1 , a surprisingly low frequency considering the downfield 13 C chemical shift.…”