Part I. Synthesis and characterization of donor-[pi]-acceptor compounds with pentadienyl-bridged indoline and tetrahydroquinoline donors and aldehyde and thiobarbituric acid acceptors : Part II. : Longitudinal study comparing online versus face-to-face course delivery in introductory chemistry /

Abstract

Part I. The design and development of organic second-order nonlinear optical (NLO) materials have attracted much interest due to their applications in optoelectronic devices and modern communications technology. Donor-pi-acceptor compounds, D-(CH=CH)n-A, often exhibit hyperpolarizability that results in laser frequency doubling (second harmonic generation) and spectroscopic solvatochromism. To study the effect of donor amine geometry upon properties associated with second-order NLO behavior in simple donor-pi-acceptor compounds, equilibrium geometries and hyperpolarizabilities (beta) for donor-acceptor polyenes with amine donors were calculated at several levels of computational theory. Two new molecules with donors that only differ by one methylene group were chosen for comparison. Thus, 5-(N-methylindolin-5-yl)-2, 4-pentadienal (1a) and 5-(N-methyl-2, 3, 4-trihydroquinolin-6-yl)-2, 4-pentadienal (2a) were synthesized in two steps from starting materials described in the literature. These aldehydes were converted into stronger acceptors in one step to give diethylthiobarbituric acid derivatives 1c and 2c, as well as tricyanofuran derivatives 1d and 2d. Positive UV solvatochromism was observed in all three derivatives. NMR solvatochromism was most pronounced in 1c, and 2c vs. 1a and 2a as measured by changes in chemical shifts. Additionally, coupling constants showed more conjugation in 1c and 2c, where 1a and 2a showed less conjugation. Finally, differential scanning calorimetry and thermal gravimetric analysis were used to compare decomposition and melting temperatures of these compounds to determine their stability. Aldehydes, 1a and 2a had distinct melting points, while the 1c, 2c, 1d, and 2d derivatives decomposed at temperatures above 150 degrees C.

Part II. This longitudinal study focused on an introductory chemistry course taught using two different modes of delivery: online and face-to-face (FtF). The sections of the course using the different delivery modes covered the same material at the same level, used the same textbook, and were taught by the same instructor. Student success was tracked over a period of nine consecutive years along with other important dependent variables including the number of developmental courses taken, student age, math and reading placement scores, overall GPA and full time status. Surprisingly, student success correlated negatively to their placement scores.

The students who chose the online course had higher overall GPA's and better placement test scores than the FtF students. Despite these advantages, online students were less successful than their FtF counterparts. This result suggests that FtF instruction was more effective, even with better students. These findings have important implications for institutions evaluating the role online instruction will play at their institutions.