Cyclic Acetals. Structural Analysis of 1,3‐Dioxepine and Related Compounds

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The He(I) PE spectra of 1,3‐dioxepine (1) and the related bicyclic acetals 1,3,7,7‐tetramethyl‐2,11‐dioxabicyclo[4.41]undeca‐3,5‐dien‐10‐one (2) and 1,3,7,7‐tetramethyl‐10‐methylidene‐2,11‐dioxabicyclo[4.4.1]undeca‐3,5‐diene (3) have been recorded and analyzed. Interpretation of the PE data indicate strong orbital interactions between the diene and acetal moieties in 1. Different conformations have been evaluated by a joint MMP2 molecular mechanics and ab initio molecular orbital analysis, which shows 1 to prefer a slightly boat‐shaped conformation with the diene part being planar and the CH2 group placed considerably out‐of‐plane. The bicyclic acetals 2 and 3 show a frontier orbital picture similar to 1 superimposed with the characteristics of the CO and CC groups, respectively. The crystal structure of the keto‐acetal 2 was determined by an X‐ray analysis.

Original languageEnglish
JournalHelvetica Chimica Acta
Issue number8
Pages (from-to)2148-2157
Number of pages10
Publication statusPublished - 1 Jan 1985

ID: 218713809