Dications of Benzylidenefluorene and Diphenylmethylidene Fluorene: The Relationship between Magnetic and Energetic Measures of Antiaromaticity

Oxidation of m- and p-substituted benzylidene fluorenes to antiaromatic dications was attempted by electrochemical and chemical means. Electrochemical oxidation to dications was successful for benzylidene fluorenes with p-methoxy, p-methyl, p-fluoro, and unsubstituted phenyl rings in the 3-position; attempts to oxidize the m-substituted derivatives via electrochemistry were unsuccessful. Chemical oxidation with SbF5/SO2ClF gave the dication of 9-[(4-methoxyphenyl)methylene]-9H-fluorene cleanly; oxidation of all other substituted benzylidene fluorenes resulted in mixtures of products. The excellent linear relationship between the chemical shifts calculated by the GIAO method and the experimental shifts for the p-methoxy-substituted benzylidene fluorene dication suggests that the calculations satisfactorily reflect the magnetic properties of this dication and potentially those of the other dications studied. The redox potentials from electrochemical oxidation, a measure of the stability of the dications, showed a good linear relationship with another measure of stability, the calculated difference in energy between each dication and its neutral precursor. The dications of benzylidene fluorenes were less stable than the dications of diphenylmethylidene fluorenes; within each type of compound, dications withp-substituted phenyl rings were more stable than dications with m-substituted phenyl rings and dications with phenyl rings substituted with electron-donating groups were more stable than dications with phenyl rings substituted with electron-withdrawing groups. The antiaromaticity of the fluorenyl system was assessed through the nucleus-independent chemical shift (NICS) that was also calculated by the GIAO method. The plot of the NICS values per square area versus the calculated energy difference for the dications showed a moderate degree of linearity; the plot of NICS values per square area versus the oxidation potentials was less linear. Thus, a suggestive, but not conclusive, relationship between magnetic and energetic measures of antiaromaticity was observed

A Study of Alternative Catalysts and Analysis Methods for Biodiesel Production

This project aims to develop a cost efficient process for biodiesel production and can be divided in three main components: 1) production of biodiesel from a variety of fuel stocks using liquid morpholine as catalyst; 2) production of biodiesel using a homogeneous phase transfer catalyst; and 3) development of a method for using Infrared Spectroscopy (IR) to determine the extent of conversion of oil to biodiesel. The production of biodiesel from various fuel stocks in the presence of methanol using liquid morpholine as catalyst reduces the problems related to purification of the biodiesel since morpholine can be recovered by distillation. Furthermore the use of two homogeneous phase transfer catalyst, tetramethylammonium hydroxide (TMAH) and choline hydroxide (CH), was evaluated. The advantage of using these catalysts is that it allows for a better separation between the fuel and glycerin, thus additionally simplifying the purification procedure. Finally, this project endeavored to develop a way to use FT-IR to determine the purity of biodiesel samples obtained since FT-IR is faster and more readily available than the standard method of gas chromatographic analysis. For educational applications, a calibration curve was created by comparing data on the purity of biodiesel samples obtained from the GC-FID analysis to the ratio of the absorbances at 1197 cm-1 to 1166 cm-1 from the FT-IR spectrum. For field application, a similar method was developed using a portable IR spectrometer. The data collected gave a good linear fit for % purity of the samples versus absorbance ratio

Dications of 3-Phenyl-indenylidene Dibenzo[ a.d ]cycloheptene: The Role of Charge in the Antiaromaticity of Cationic Systems

Dications of 9-(3-phenyl-1H-inden-1-ylidene)-5H-dibenzo[a,d]cycloheptene, 52+, were prepared by oxidation with SbF5 in SO2ClF, and their magnetic behavior was compared to dications of 9-(3-phenyl-1H-inden-1-ylidene)-9H-fluorene, 22+. The good correlation between the experimental 1H NMR shifts for the dications that were oxidized cleanly and the chemical shifts calculated by the GAIO method supported the use of the nucleus independent chemical shifts, NICS, to evaluate the antiaromaticity of the indenyl systems of 22+/52+ and their unsubstituted parent compounds, 62+ and 72+, as well as the antiaromaticity of the fluorenyl system of 22+/72+ and the aromaticity of the dibenzotropylium system of 52+/62+. Antiaromaticity was shown to be directly related to the amount of charge in the antiaromatic systems, with the antiaromatic systems more responsive to changes in the calculated NBO charge than the aromatic systems. The antiaromaticity was also shown to be directly related to the amount of delocalization in the ring system. The aromaticity of the dibenzotropylium system was much less responsive to changes in the amount of charge in the tropylium system, because the aromatic system was much more completely delocalized. Thus, antiaromatic species are more sensitive probes of delocalization than aromatic ones