Conformation of 1,3-dioxans

The most stable conformation of 1 3 dioxan 5 ol is the chair form that has its hydroxyl group in an axial orientation Suggest a reasonable explanation for this fact Building a molecular model IS helpful... 

The preferred conformer of 1,3-dioxane is the chair form, as proved by photoelectron spectroscopy (85MI2) and, mainly, by NMR spectroscopy... 

Conformation of 1,3-Dioxane-2-ylium Ions and the Corresponding Carbanions... 

The X-ray structures of two anthraquinone derivates of 1,3-dioxane were published. In both 1 -methoxy-4-(2-methylprop-2-enyloxy)-2-[(2i ,6i )-4,4,6-trimethyl-1,3-dioxan-2-yl]-anthraquinone and 4-hydroxy-3-(2-methyl prop-2-enyloxy)-2-[(27 ,67 )-4,4,6-trimethyl-l,3-dioxan-2-yl]anthraquinone the 1,3-dioxane ring adopts the chair conformation and the substituents in positions 2 and 6 are in equatorial conformations (99AX(C)436). Finally, Freeman et al. (02JMS(T)43), employing both ab initio theory and density function theory, calculated the energies of chair, half-chair, sofa, twist, and boat conformers of 1,3-dioxane. 

The conformations of 1,3-dioxans have been well investigated for example, for methyl derivatives, by the use of isotope n.m.r., microwave spectroscopy, and the relationship with retention time in g.l.c. ... 

Further work on non-chair conformations of 1,3-dioxans has been reported by the group in Stirling. - They point out that there should be two twist conformations of the 1,3-dioxan ring, viz. 1,4-twist (13) and/or 2,5-twist (14), depending upon which ring atoms lie on the (quasi) two-fold... 

Explain why the most stable chair conformation of 1,3-dioxan-5-ol has an axial hydroxyl group, but the most stable chair conformation of 5-methoxy-l,3-dioxane has an equatorial methoxy group. 

Conformation of l,3-Dioxan-2-ones, 1,3-Dioxan-4-ones, and Meldrum s... 

The presence of twist-boat forms in the conformational equilibria of 1,3-dioxane derivatives due to the presence of 1,3-diaxial interactions was corroborated by force field calculations [77T2237 79T691, 79T1945]. 

Preferred Confobmers and Conformational Equilibria of 1,3-Dioxan-2-ones in CDCL AT Room Temperature [83ACSA(B)289]... 

Eliel, E. L. Nader, F. W. Conformational analysis. XX. The stereochemistry of reaction of Grignard reagents with ortho esters. Synthesis of 1,3-dioxanes with axial substituents at C-2.]. Am. Chem. Soc. 1970, 92, 584-590. 

The infrared spectra of the saturated heterocycles in this series show characteristic C—O (1300-1020 cm ) and C—S (800-600 cm ) stretching vibrations. The v(C—O) are often found to be the stronger. In the case of 1,3-dioxane, IR has been used as a structural probe for ring conformation, and the conclusions are in agreement with those from other methods <70JCP(53)376>. 

Kaloustian MK, Dennis N, Mager S, Evans SA, Alcudia F, Eliel EL (1976) Confinmational analysis. XXX. Conformational equilibria of 1,3-dioxanes with polar substituents at C-5. J Am Chem Soc 98 956-965... 

Computer simulation of conformational transformations of 1,3-dioxanes and their 2-siLa and 2-bora analogs 13ZOR1247. 

Table 3.8. Comparison of Conformational Free-Energy Values for Substituents on Tetrahydropyran, 1,3-Dioxane, and 1,3-Dithiane Rings with Those for Cyclohexane...

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