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DHP rings in these structures display a range of conformations near the half-chair form but distorted variously toward each of the two inequivalent d,e- and e,f-diplanar forms. Factor analysis reveals the coordination of torsional motions associated with a principal ring-bending mode based on the various ring conformations. Two methyl ketals and an hemiketal structure are reported. (I): (2S,4S)-cis-2-methoxy, C15H16O4, Mr = 260·30, trigonal, P3221, a = 9·579 (5), c = 24·938 (15) Å (hexagonal axes), V = 1981·7 (33) Å, Z = 6, Dx = 1·309 g cm-3, λ(Mo Kᾱ)= 0·71073 Å, μ = 0·884 cm- 1, F(000) = 828, T = 295 K, R = 0·040 for 1470 observations. (II): (2R,4S)-trans-2-methoxy, C15H16O4, Mr = 260·30, monoclinic, P21, a = 9·254 (4), b = 11·970 (5), c = 12·736 (5) Å, β = 105·64 (4)°, V = 1358·5 (22) Å3, Z = 4 (two molecules per asymmetric unit), Dx = 1·274 g cm-3, λ(Mo Kᾱ) = 0·71073 Å, μ = 0·860 cm-1, F(000) = 552, T = 295 K, R = 0·043 for 2923 observations. (III): (2S,4S)-cis-2-hydroxy, C14H14O4, Mr = 246·27, orthorhombic, P212121, a = 6·816 (3), b = 12·826 (7), c = 13·949 (6) Å, V = 1219·4 (17) Å3 , Z = 4, Dx = 1·340 g cm-3, λ(Mo Kᾱ) = 0·71073 Å, μ= 0·919 cm-1, F(000) = 520, T = 293 K, R = 0·046 for 1291 observations."},{"label":"DOI","value":"10.1107/S0108768191000423"},{"label":"Volume","value":"47"},{"label":"Issue","value":"4"},{"label":"Publication Date","value":"D:00 M:08 Y:1991"},{"label":"Publication Information","value":"Copyright 1991 International Union of Crystallography. The original published version of this article may be found at http://dx.doi.org/10.1107/S0108768191000423."}],"description":"Dihydropyran Ring Conformations. I. 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