1976
DOI: 10.3987/r-1976-02-0293
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A Review on the Conformational Aspects in the 1,3-Dioxane System

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Cited by 105 publications
(46 citation statements)
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“…45 Molecular mechanics calculated the 1,4-twist (2a) and 2,5-twist (2b) conformers to be 3.1 kcal/mol and 4.2 kcal/mol, respectively, higher in energy than the chair conformer (1). 29,30 The HF chair (1)-1,4-twist (2a) free energy difference (⌬GЊ c-t ϭ 4.93 for 1,4-dithiane at 298.15 K was comparable to the estimated experimental value for cyclohexane (⌬GЊ c-t ϭ 4.9 kcal/mol), 6 lower than some of the estimated experimental values for 1,3-dioxane (⌬GЊ c-t ϭ 5.7 kcal/ mol), 6,13,68 and larger than the estimated experimental values for 1,3-dithiane (⌬GЊ c-t ϭ 2.9 kcal/mol). ‡ ) is 3.151 Å, which is less than the sum of the van der Waals radius (r vdw ϭ 1.80 Å) for sulfur.…”
Section: Resultsmentioning
confidence: 91%
“…45 Molecular mechanics calculated the 1,4-twist (2a) and 2,5-twist (2b) conformers to be 3.1 kcal/mol and 4.2 kcal/mol, respectively, higher in energy than the chair conformer (1). 29,30 The HF chair (1)-1,4-twist (2a) free energy difference (⌬GЊ c-t ϭ 4.93 for 1,4-dithiane at 298.15 K was comparable to the estimated experimental value for cyclohexane (⌬GЊ c-t ϭ 4.9 kcal/mol), 6 lower than some of the estimated experimental values for 1,3-dioxane (⌬GЊ c-t ϭ 5.7 kcal/ mol), 6,13,68 and larger than the estimated experimental values for 1,3-dithiane (⌬GЊ c-t ϭ 2.9 kcal/mol). ‡ ) is 3.151 Å, which is less than the sum of the van der Waals radius (r vdw ϭ 1.80 Å) for sulfur.…”
Section: Resultsmentioning
confidence: 91%
“…In all the investigated structures the 1,3-dioxane rings exhi- bit chair conformations and the bond lengths, bond angles, and torsion angles show normal values. [26] In 5a the dihedral angles between the best plane of each heterocycle (the plane formed by the exocyclic bonds of the acetal carbon atom) and the plane of the corresponding aromatic ring exhibit values close to 90°( C 7 The investigated crystal of 5b (selected from the mixture of isomers) contains a centrosymmetric molecule (group P 21/c) and represents the unlike isomer. Two of the aromatic rings exhibit orthogonal disposition (…”
Section: Solid-state Molecular Structuresmentioning
confidence: 99%
“…A Ph ϭ 13.04 kJ/mol) [26] determines the strong shifting of the conformational equilibria involving the flipping of the 1,3-dioxane rings towards the conformer with both aryl groups in equatorial orientation. Owing to the chirality of the spiro skeleton, these compounds show separable enantiomers and are obtained under the usual conditions of the acetalisation reaction as racemic mixtures (P and M configurations of the helix, Scheme 2).…”
Section: Introductionmentioning
confidence: 99%
“…Four configuration isomers are possible: cis-cis-cis (I); cis-cis-trans (II); cis-trans-trans (III) and trans-trans-trans (IV) (Scheme 7). The A-values of methyl and ethyl substituents at position 5 of the 1,3-dioxane ring are very close (A Me = 3.7 kJ/mol [10]; A Et = 3.3 kJ/mol [10]), while the aromatic substituent in the ketal part (positions 2', 2", 2"') strongly prefers the axial orientation. The isomers of 5 exhibit anancomeric structures (as the NMR spectrum of the row product shows) with axial orientation of the aromatic group and with statistically equal axial and equatorial orientations of the methyl and ethyl groups at positions 5', 5" and 5"'.…”
Section: Scheme 4 Synthesis Of Compdmentioning
confidence: 96%