Abstract Solvolysis of a series of threo-2-aryl-1-methylpropyl brosylates (p-MeO, p-Me, H, p-Cl, m-Cl, m-CF3, and p-NO2; 1a–g) has been carried out in four carboxamides, N-methylformamide (NMF), N-methylacetamide (NMA), N,N-dimethylformamide (DMF), and N,Ndimethylacetamide (DMA), as solvent. Fractions of ks and FkΔ pathway were determined on the basis of the upward drift from the Hammett plot of the rate constant (kt); the extra acceleration by p-MeO and p-Me substituents was assigned to the FkΔ fraction. The FkΔ⁄kt values were not in agreement with the amount of retained products (threo-acetate and threo-alcohol) obtained in NMA and DMA solvolysis of 1a–c, although they should be in line with each other on the basis of the bridged-ion theory. The C(2)-deuterated phenyl derivative (1c-2-d) was solvolyzed in NMF, NMA, and DMF to give retained carboxylates (acetate or formate). However, the isotope scrambling at C(2) and C(1) of the carboxylates is incomplete, indicating that a symmetrical ion, such as a phenyl-bridged ion, can not be the intermed be the intermediate of the carboxamide solvolysis. A good correlation of logkt for substrates (1a–g) with log(% threo-acetate% erythro-acetate) or with log (% threo-acetate% olefinic products) was found for solvent systems such as NMA, DMA, and acetic acid, indicating that the reactions of all substituted substrates can be explained by intervention of a common intermediate [R+X−], a classical tight ion-pair from which the final products are derived. Such reactivity-selectivity relationship also holds between log kt’s of 1c in a series of carboxamide and logarithms of threo-erythro ratio in acetate or formate. Through-space interaction between a face of aryl ring and carbenium ion center in the transition state is considered as a possible cause for the anomalous acceleration by the activating aryl groups.