NMR experiments on acetals. part 54. Rotameric behaviour of geminal 4‐, and 5‐phenylgroups in 1,3‐dioxanes
- 1 January 1974
- journal article
- research article
- Published by Wiley in Bulletin des Sociétés Chimiques Belges
- Vol. 83 (9-10) , 357-368
- https://doi.org/10.1002/bscb.19740830907
Abstract
The 1H‐NMR spectra were studied of a series of 2‐Me‐5‐R‐5‐ø1,3‐dioxanes (5) (R = H, Me, Et, i.Pr; ø of 2‐Me‐spiro(1,3‐dioxane‐5,9′‐fluorene) (14), of 5‐R‐4,4‐diø‐1,3‐dioxanes (14) (R = Me, Et, n.Pr, i.Pr and i.Bu) and of 5‐R‐spiro(1,3‐dioxane‐4,2′‐adamantane) (7) (R = Me, Et, n.Pr, i.Pr, ø). From a comparative shift study, the preferential orientation of the phenylgroups in the ø‐substituted 1,3‐dioxanes were ascertained. In (10) and (10) the 5‐ø‐axial groups are bisectional (14). The 5‐ø‐equatorial groups are bisectional in the 5‐R‐5‐ø‐derivatives with R = H and Me, but flatsided with the larger substituents R = Et, i.Pr, ø. (See Chart I). For the 4,4‐diø‐derivatives, both aromatic rings are flatsided (10). In order to reach this conclusion comparison between (10) and (14), where the 5‐R‐groups occupy the axial positions, was essential. A rational explanation for the behaviour of the non‐spherical phenyl groups is offered.Keywords
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