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Cyclic Acetals. Structural Analysis of 1,3‐Dioxepine and Related Compounds
Author(s) -
Jørgensen Flemming S.,
Gajhede Michael,
Frei Bruno
Publication year - 1985
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.19850680809
Subject(s) - chemistry , bicyclic molecule , acetal , molecular orbital , diene , ab initio , stereochemistry , group (periodic table) , computational chemistry , crystallography , molecule , organic chemistry , natural rubber
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 CH 2 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 CO and CC groups, respectively. The crystal structure of the keto‐acetal 2 was determined by an X‐ray analysis.