title: Energetics of oxaspirocycle prototypes: 1,7-dioxaspiro[5.5]undecane and 1,7,9-trioxadispiro[5.1.5.3]hexadecane.
abstract: The relative gas-phase energetics of several low-lying isomers of 1,7-dioxaspiro[5.5]undecane and 1,7,9-trioxadispiro[5.1.5.3]hexadecane have been calculated with second-order Mller-Plesset perturbation theory and basis sets as large as aug-cc-pVQZ. Relative energies in THF, dichloromethane, acetone, and DMSO have been estimated with corrections from polarized continuum model calculations at the B3LYP/6-311+G(d) level. In the most stable conformation of 1,7-dioxaspiro[5.5]undecane, both rings adopt chair conformations, and both oxygens are axially disposed (2A). It is more than 2 kcal mol(-1) more stable than all the other conformers. In agreement with previous work, the "twist-boat" trans isomer (3A) is the most stable isomer of 1,7,9-trioxadispiro[5.1.5.3]hexadecane. However, in contrast to this earlier study, an "all-chair" conformation (3B) is found to be the most stable cis isomer of 1,7,9-trioxadispiro[5.1.5.3]hexadecane (E approximately 0.5 kcal mol(-1) in acetone and DMSO). Gauge-independent atomic orbital computations at the B3LYP/6-311+G(d) level indicate that this is the only cis isomer with (13)C NMR chemical shifts that are qualitatively consistent with the experimental spectra.
authors.affiliation: Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677-1848, USA.
authors.forename: Abby Jones
authors.initials: AJ
authors.lastname: Weldon
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Tschumper
mesh_terms: D003516:Cycloparaffins / Q000737:chemistry*; D008958:Models, Molecular; D013141:Spiro Compounds / Q000737:chemistry*
chemical_list: C516985:1,7,9-trioxadispiro(5.1.5.3)hexadecane; D003516:Cycloparaffins; D013141:Spiro Compounds; C103434:1,7-dioxaspiro(5.5)undecane