Ab initio analysis of the energy and geometry during the rearrangement of cyclopentadienylboranes and the evaluation of the dapsic computer tutorial.

Abstract

The equilibrium and transition state geometries of the degenerate 1,5-sigmatropic rearrangement of cyclopentadienylborane, cyclopentadienyldifluroborane, cyclopentadienyldichloroborane, pentamethylcyclopentadienylborane, pentamethylcyclopentadienyldifluroborane, and pentarnethylcyclopentadienyldichloroborane were optimized using ab initio (RHF/3-21G*, RHF/6-31G*, RMP2/3-21G*, and RMP2/6-31G*) calculations. Activation energies were predicted and compared with previously published experimental data [P. Jutzi, B. Krato, M. Hursthouse, A. J. Howes, Chem. Ber. (1987), 120, 565--574.] The molecule optimized to an asymmetrical geometry with the boron atom shifted away from its symmetric h1 position and toward one of the two neighboring carbons. This geometry was predicted for each molecule at each level of theory except for C 5H5BH2 at the RMP2/6-31G* level and C5H 5BH2 at the RHF/6-31G* level. This geometry was also predicted for bis(pentamethylcyclopentadienyl)fluoroborane.

Also, a computer aided instruction program called DAPSIC was evaluated for effectiveness in introductory college chemistry classes at MTSU. DAPSIC was designed to teach unit conversions using the factor-label method (also known as dimensional analysis or unit analysis.) Student performance on a brief quiz before and after using DAPSIC was compared with student performance on a brief quiz before and after doing an equivalent worksheet assignment. In the chemistry class intended for non-majors, the improvement in the quiz scores of students who used DAPSIC was significantly greater than the improvement in the quiz scores of students who used the worksheet. No significant difference was seen in the chemistry major's introductory class. In both classes, students over age 22 who used DAPSIC also showed significantly greater improvement over students age 22 who used the worksheet.