1H, 13C, and 31P NMR spectra of a series of alkyltriarylphosphonium salts, (p-XC6H4)3P+R I- (R = Me, CH2CMe3, and CH2SiMe3; X = H, Me, OMe, and NMe2) are reported. Their chemical shifts and coupling constants, 1JPC and 2JPH, are rationalized in terms of hyperconjugative π bonding between the α C—H bonds and 3d orbitals of phosphorus. NMR including 15N spectra of Ph3P+NHR BF-, where R = H, Me, CMe3, NH2, and NMe2, have also been determined. Relative changes in their parameters are discussed in the light of interaction between the lone pair of nitrogen and d orbitals of phosphorus, and compared vs. those due to hyperconjugative π bonding in the alkyltriarylphosphonium salts. Temperature effects on their spectra are reported and interpreted in terms of changes in bonding around. phosphorus... as a result of inversion at the α nitrogen.