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Activation Energies and Reaction Energetics for 1,3‐Dipolar Cycloadditions of Hydrazoic Acid with CC and CN Multiple Bonds from High‐Accuracy and Density Functional Quantum Mechanical Calculations
Author(s) -
Jones Gavin O.,
Ess Daniel H.,
Houk Kendall N.
Publication year - 2005
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200590134
Subject(s) - hydrazoic acid , chemistry , acetylene , transition state , enthalpy , tetrazole , computational chemistry , density functional theory , adduct , thermodynamics , organic chemistry , catalysis , physics
The reactions of hydrazoic acid (HN 3 ) with ethene, acetylene, formaldimine (H 2 CNH), and HCN were explored with the high‐accuracy CBS‐QB3 method, as well as with the B3LYP and mPW1K density functionals. CBS‐QB3 predicts that the activation energies for the reactions of hydrazoic acid with ethylene, acetylene, formaldimine, and HCN have remarkably similar activation enthalpies of 19.0, 19.0, 21.6, and 25.2 kcal/mol, respectively. The reactions are calculated to have reaction enthalpies of −21.5 for triazoline formation from ethene, and −63.7 kcal/mol for formation of the aromatic triazole from acetylene. The reaction to form tetrazoline from formaldimine has a reaction enthalpy of −8 kcal/mol (ΔG rxn =+5.6 kcal/mol), and the formation of tetrazole from HCN has a reaction enthalpy of −23.0 kcal/mol. The trends in the energetics of these processes are rationalized by differences in σ ‐bond energies in the transition states and adducts, and the energy required to distort hydrazoic acid to its transition‐state geometry. The density functionals predict activation enthalpies that are in relatively good agreement with CBS‐QB3, the results differing from CBS‐QB3 results by ca. 1–2 kcal/mol. Significant errors are revealed for mPW1K in predicting the reaction enthalpies for all reactions.