Issue in Honor of Prof. Waldemar Adam ARKIVOC 2007 (viii) 257-272
Theoretical studies on thermal stability of alkyl-substituted 1,2-dioxetanes
Erick L. Bastosa and Wilhelm J. Baaderb,*
aCentro de Ciências Naturais e Humanas, Fundação Universidade Federal do ABC. Rua Santa Adélia, 166. 09210-170 Santo André/SP Brazil bInstituto de Química, Universidade de São Paulo. Av. Prof. Lineu Prestes, 748 Bl. 12S. 05508900 São Paulo/SP Brazil E-mail: wjbaader@iq.usp.br
Dedicated to Prof. Waldemar Adam on the occasion of his 70th birthday
Abstract
The geometry of thirty alkyl-substituted 1,2-dioxetanes derivatives was optimized using theoretical methods. It was found that AM1 and PM3 semiempirical methods do not adequately predict dihedral angles of the peroxidic ring of highly stabilized 1,2-dioxetanes. Geometric parameters calculated by ab initio and hybrid DFT methods are in better agreement with experimental activation parameter data than the one obtained by semiempirical calculations. Among those, the B3LYP method with the 6-31G(d) basis set is the most adequate one. Very good correlation between theoretical carbon-carbon bond distances and experimental activation parameters was found for all ab initio and hybrid DFT methods, whereas, oxygen-oxygen bond distances and dihedral angles do not correlate well with the activation parameters. Results obtained by different methods are compared and a qualitative explanation for the stabilization effect of alkyl groups on the 1,2-dioxetane ring is proposed.
Keywords: 1,2-Dioxetanes, thermal stability, quantum mechanics.
Introduction
1,2-Dioxetanes constitute a large class of isolable high-energy molecules whose uncatalyzed thermal decomposition generates electronically excited products in considerable yields.1,2 These products are formed preferentially in the electronically excited triplet state and the mechanism of this transformation was extensively studied during the 1970’s and mid 1980’s.1,3-7 As consequence, several hundreds of 1,2-dioxetane derivatives were synthesized.3-6 Among them, those originated from hindered olefins have shown remarkable thermal stability.8
ISSN 1424-6376 Page 257 ©ARKAT USA, Inc.
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