title: DFT study of [2.2]-, [3.3]-, and [4.4]paracyclophanes: strain energy, conformations, and rotational barriers.
abstract: The three smallest symmetrical paracyclophanes, having tethers with two, three, or four methylene groups, have been examined with four density functional methods (B3LYP, M06-2x, B97-D, ωB97X-D). The geometries predicted by functionals accounting for medium-range correlation or long-range exchange and/or dispersion are in close agreement with experiment. In addition, these methods provide similar estimates of the strain energy of the paracylcophanes, which decrease with increasing tether length. [4.4]Paracyclophane is nearly strain-free, reflecting the small out-of-plane distortion of its phenyl rings. Lastly, the barrier for interconversion of the conformers of [3.3]paracylcophane is computed in close agreement with experiment, and an estimate for phenyl rotation in [4.4]paracyclophane of about 19 kcal mol(-1) is predicted by the DFT methods employed.
authors.affiliation: Department of Chemistry, Trinity University, 1 Trinity Place, San Antonio, Texas 78212, USA. sbachrach@trinity.edu
authors.forename: Steven M
authors.initials: SM
authors.lastname: Bachrach