NMR Experiments on Acetals. Part 28. 1,3‐Dioxanes with Non‐Chair Conformations and the ²J(Och₂O) Criterium

Several 1,3‐dioxanes, not possessing chair conformations (Chart 1), are newly prepared. The PMR data are discussed in terms of possible conformations. Typically 2 J(OCH 2 O) coupling constants are too positive in accordance with disturbed torsional relations between σ(C 2 –H) bonds and adjacent p (0) lobes. A semiquantitative discussion, relating 2 J with presumed torsion ring angles, is given. Thus values for 2 J(OCH 2 O) in carbon disulfide are: — 5.5 cps for a twist conformation, with (idealized) torsion angles of 30° and 60° (form ( 14 )); ‐3.4 cps for a conformation between a chair form a half‐chair form and sofa form (resp. ( 16 ) and ( 17 )); and — 4.7 cps for a form close to a classical boat ( 19 ) with torsion angles of 0° and 60°. P.D. and G.S. tank the IWONL for a scholarship.