Semiempirical prediction of the thermochemistry of intermediates involved in the cyclic mechanism of hindered amine stabilizers

Abstract

The suitability of the AM1 computational method for predicting the thermochemistry of amine derivatives related to the functioning of hindered amine light stabilizers (HALS) was established by comparing computed data with representative published experimental data for HALS-related intermediates. Thus, AM1 accurately predicts the relative energies of 2,2,6,6-tetramethyl-4-oxopiperidine, 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl and 1-hydroxy-2,2,6,6-tetramethyl-4-oxopiperidine. The AM1 method was then utilized to estimate key bond dissociation energies for which experimental values do not exist. For the 2,2,6,6-tetramethyl-4-oxopiperidine series the following bond strengths are predicted: NO • = 366 kJ/mol; NOH = 234 kJ/mol; NOH = 296 kJ/mol; NOCH 3 = 176 kJ/mol; NOCH 3 = 185 kJ/mol; NOCH 2H = 359 kJ/mol; NOC 2H 5 = 164 kJ/mol; NOC 2H 5 = 172 kJ/mol; NOCH 2HCH 3 = 344 kJ/mol; NOCH(CH 3) 2 = 143 kJ/mol; NOCH(CH 3) 2 = 154 kJ/mol; NOCH(CH 3) 2 = 333 kJ/mol. The data should be of general value for the thermodynamic evaluation of proposed HALS mechanisms.