Long-range phosphorus-31-hydrogen-1 spin-spin couplings in benzyl and tolyl phosphorus compounds

Abstract

Examination of the spectra of a series of tolyl-and benzylphosphonium salts, phosphonates, and phosphine oxides shows the existence of two types of long-range 31P-1H spin-spin couplings. Four-bond allylic couplings (1-2.5 Hz) are observed in both series of compounds; the magnitude of 4 J~~ depends upon the position of attachment (sp2 or sp3 carbon) of phosphorus to the allylic triad. Both five-and seven-bond homoallylic couplings are observed in the benzylphosphorus systems. The magnitudes of 'JPH (2.3-2.6 Hz) are greater than those of ?]pH (1 ,1-1,7 Hz). Neither six-bond couplings in the benzyl series nor five-and six-bond couplings in the tolyl analogs are observed. Both inductive hyperconjugation and overlap hyperconjugation coupling mechanisms are considered for the homoallylic interactions; on the basis of certain consistent patterns of JPH behavior and the study of model compounds, the latter mechanism is favored.nvestigations of the proton magnetic resonance spectra

Dependence of the long‐range phosphorus–hydrogen coupling constant nJP–H (n = 3,6,7) on the bond order between phosphorus and its substituents: preparation and spectroscopic characterization of several phosphoramidates

“…2 Griffin, 3 Stothers and Robinson 4 and Berry et al 5 have reported the correlation between the hybridization state of the phosphorus atom with proton shift and spin-spin coupling constant J P -H , which was interpreted by Hendrickson et al 6 The influence of benzene on the 1 H NMR spectra of mononuclear phosphorus(V) amides and dimethylamino cyclotriphosphazatrienes is described by Keat and Shaw. 7 Several other publications have described the short-and long-range J P -H in phosphorus compounds 3 -22 and four-and five-bond coupling constants ( 4 J P -H , 5 J P -H ) in allylic and homoallylic phosphorus compounds. 11,13,14,19,22 The observations of five, six, and seven bond couplings in isomeric methylbenzylphosphonium salts have been reported by Khaleeludin and Scott 15 and Gordon and Griffin 14,16 and some other studies have reported 3 J P -H spin-spin coupling too. 6,16 In the above-mentioned studies, several models have been put forward to explain the mechanism of long-range Ł Correspondence to: K. Gholivand, Department of Chemistry, Tarbiat Modarres University, PO Box 14155-4838, Tehran, Iran.…”

“…11,13,14,19,22 The observations of five, six, and seven bond couplings in isomeric methylbenzylphosphonium salts have been reported by Khaleeludin and Scott 15 and Gordon and Griffin 14,16 and some other studies have reported 3 J P -H spin-spin coupling too. 6,16 In the above-mentioned studies, several models have been put forward to explain the mechanism of long-range Ł Correspondence to: K. Gholivand, Department of Chemistry, Tarbiat Modarres University, PO Box 14155-4838, Tehran, Iran. E-mail: gholi kh@net1cs.modares.ac.ir spin-spin coupling, 16 and among them is the hyperconjugation mechanism that was first suggested by Bersohn 23 in 1962.…”

“…6,16 In the above-mentioned studies, several models have been put forward to explain the mechanism of long-range Ł Correspondence to: K. Gholivand, Department of Chemistry, Tarbiat Modarres University, PO Box 14155-4838, Tehran, Iran. E-mail: gholi kh@net1cs.modares.ac.ir spin-spin coupling, 16 and among them is the hyperconjugation mechanism that was first suggested by Bersohn 23 in 1962. On the basis of this mechanism, Khaleeludin and Scott 15 interpreted the long-range coupling in methylbenzylphosphonium salt.…”

“…The interaction decreases in the order of para > ortho > meta. 16 Allen et al 24 and Gulick et al 25 have, in fact, rationalized the coupling constant in a series of semiquinone phosphate radicals in terms of a hyperconjugative mechanism.…”

“…Finally, Griffin and Gordon observed that there exists a long-range coupling in tris-p-tolylphosphonic dichloride, 16 which provides evidence against the importance of hyperconjugation as a mechanism for putting -character into the phosphorus-carbon bond.…”