Kinetic and thermodynamic study of the substituent effect on the amino-Claisen rearrangement of para-substituted N-allyl-N-arylamine: a Hammett study via DFT

Abstract

In order to find the susceptibility of the amino-Claisen rearrangement and the next proton shift reaction of N-allyl-N-arylamine to the substituent effects in the para position, the kinetic and thermodynamic parameters were calculated at the B3LYP level using the 6-31G^** basis set. The calculated activation energies for the rearrangements and proton shift reactions are close to 44.4 and 49.5 kcal mol^− 1, respectively. The transition states of the rearrangement with electron-donor substituents are more stable than those with electron-withdrawing substituent groups, but for the proton shift reaction, this situation is reversed (with the exception of fluorine atom for the rearrangement and fluorine and chlorine atoms for the proton shift reaction). Negative values for the activation entropy confirm the concerted mechanism for the amino-Claisen rearrangement and proton shift reaction. The Hammett ρ values of − 2.4172 and − 1.7791 are obtained for σ_p and σ⁻  (enhanced sigma) in the amino-Claisen rearrangement, respectively. The correlation between log(k _X/k _H) and σ_p is weaker than that with σ⁻  (enhanced sigma). A negative Hammett ρ value indicates that the electron-donating groups slightly increase the rate of amino-Claisen rearrangement. A positive Hammett ρ value (2.4921) for the proton shift reaction indicates that electron-withdrawing groups increase the rate of reaction.

Keywords:

• Hammett
• density functional theory
• substituent effect
• amino-Claisen rearrangement
• N-allyl-N-arylamine

Notes

1. Ph.D. Student.