Substituent effects on 13C NMR chemical shifts in dialkylaminophenylchlorophosphines

• Published in: Polyhedron Vol. 11; no. 21; pp. 2759 - 2766
• Main Authors: Marathias, Vasilios, Turnbull, Mark M., Abdon, Robert L., Coppola, Brian P.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1992; New York, NY Elsevier Science
• Subjects: Atomic and molecular physics; Exact sciences and technology; Molecular properties and interactions with photons; Nuclear resonance and relaxation; Physics; Substituent effect; Spin spin coupling constant; Chemical shift; Amine; NMR parameter; Tertiary phosphine; Twist angle; Benzenic compound; Experimental study; NMR spectrum; Organic compounds
• ISSN: 0277-5387
• DOI: 10.1016/S0277-5387(00)83633-5

The relative chemical shifts and 2 J(PC) coupling constants in the low-temperature limiting spectra of a series of Ph(R 2N)PCl compounds [R  Me, Et, PhCH 2, iPr and c-Hex] differ for R  primary or secondary. For primary alkyl substituents, the more downfield signal exhibits a large, positive coupling and the more upfield resonance shows a small, negative coupling. These observations are reversed for secondary alkyl substituents. Calculated minimum-energy molecular structures indicate that the source of this reversal does not lie in differences in conformation about the PN bond. Analysis of the high- and low-temperature limiting spectra of a series of Ph(RR′N)PCl compounds [R, R′  Me, Et, Bz, iPr and c-Hex] suggests that the NC carbon syn to the phosphorus lone-pair is subject to a relatively constant deshielding effect from the phosphorus-lone pair and a shielding contribution from the anti substituent that increases with increasing bulk of that anti substituent. Conversely, the chemical shift of the carbon anti to the phosphorus lone-pair is relatively insensitive to changes in the syn substituent, giving rise to the observed chemical shift reversal.