Date of Award

1-1-1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

Electron donor acceptor complexes of the donors biphenylene (BP) and some ferrocenes have been studied by NMR spectroscopy to examine the effects of donor ring currents on acceptor chemical shifts.Equilibrium constants and the differences in chemical shifts between free and complexed acceptor ((DELTA)(,o) values) for the complexes of BP with the acceptors 1,3,5-trinitrobenzene (TNB), 1,4-dinitrobenzene (DNB), N-methylsuccinimide (NMS), tetrafluoro-1,4-benzoquinone (FAN), and 1,4-dicyano-2,3,5,6-tetrafluorobenzene (TFTN) have been obtained by ('1)H and ('19)F NMR spectroscopy. In addition, the crystal and molecular structures of the 1:1 complexes BP-DNB and BP-FAN have been determined by x-ray diffraction. The complexes crystallize in infinite stacks of alternating BP and acceptor molecules separated by 3.54(ANGSTROM) and 3.26(ANGSTROM) for BP-DNB and BP-FAN, respectively. Both acceptors are approximately centered over the four-membered BP ring and tilted slightly with respect to the mean plane of BP; the dihedral angles are 10.1(DEGREES) and 3.0(DEGREES) for BP-DNB and BP-FAN, respectively. The equilibrium constants obtained show BP is a relatively good donor; however the (DELTA)(,o) values obtained are significantly smaller than literature values for complexes of the same acceptors with methyl-substituted benzenes of similar complexing ability. The (DELTA)(,o) values obtained from ('19)F NMR can be explained on the basis of both charge-transfer and ring currents affecting the ('19)F (DELTA)(,o) values. These results are consistent with several quantum-mechanical calculations that suggest the presence of a paramagnetic ring current in the central four-member ring of BP.Equilibrium constants and (DELTA)(,o) values for the complexes of ferrocene (FER) and 1,1'-dimethylferrocene with TNB have been obtained using NMR spectroscopy. In addition, the equilibrium constants for the complexes of FER and ruthenocene (RUT) with TNB were determined using visible spectroscopy, as the observed changes in chemical shift were not large enough to determine the RUT-TNB equilibrium constant and (DELTA)(,o) value from NMR spectroscopy. Although the equilibrium constant value indicated FER is a better donor than benzene, the (DELTA)(,o) value obtained for the complex of FER with TNB is (TURN)60% that of the literature value for the benzene-TNB complex. Further, the visible spectroscopic measurements indicated RUT is a somewhat better donor than FER, and a calculation of (DELTA)(,o) for the RUT-TNB complex using the equilibrium constant obtained from the spectroscopic measurements and the observed (DELTA) values indicate the RUT-TNB (DELTA)(,o) value is (TURN)40% that of the benzene-TNB complex. These results are consistent with the presence of ring currents in the FER and RUT cyclopentadienyl rings of magnitudes compatible with the smaller ring size and the number of (pi) electrons in the rings. The 1,1'-dimethylferrocene complex with TNB shows an increase in the value of the equilibrium constant and a decrease in the (DELTA)(,o) value analogous to the literature values for benzene and toluene complexes with TNB.The results of the studies of biphenylene and ferrocene complexes are consistent with calculated values of ring currents for these molecules. Thus, the study of acceptor chemical shifts has shown to be a method of confirming theoretical calculations of donor ring currents, or alternately, a method of experimentally evaluating donor ring currents.

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