A series of bis(arylnitrene) compounds was generated for studies by ESR spectroscopy at cryogenic temperature. Zfs $\vert$D/$h$c$\vert$ and $\vert$E/$h$c$\vert$ were determined and temperature dependent studies were done on some of the bis(arylnitrene)s. Bis(p-phenylnitrene) compounds were generated, and their ESR spectra showed mononitrene signals and triplet dinitrene signals including $\Delta$m$\sb{\rm s}$ = 2 transitions. Zfs $\vert$D/$hc\vert$ of mononitrenes and triplet dinitrenes decreased as conjugation between phenylnitrenes increased. Zfs $\vert$E/$h$c$\vert$ was estimated to be zero except for 1,4-phenyldinitrene. The temperature dependent studies concluded that all bis(p-phenylnitrene)s have ground state singlets. Triplet zero field splitting observed for bis(p-phenylnitrene)s are due mostly to one-center interaction of $\sigma$ and $\pi$-electrons of the nitrenes. Three biphenyldinitrenes were generated: the 4,4$\sp\prime$-isomer, 3,4$\sp\prime$-isomer, and 3,3$\sp\prime$-isomer. The 4,4$\sp\prime$-isomer showed an ESR spectrum typical of a triplet dinitrene, and a temperature study showed a singlet ground state. The 3,4$\sp\prime$-isomer showed a complex ESR spectrum typical of a quintet state, and a temperature study showed a ground state quintet. The 3,3$\sp\prime$-isomer showed only a mononitrene signal in the ESR spectrum, so it is presumed to be a disjoint compound with almost no interaction between nitrene sites. Three phenylether dinitrene compounds were generated for comparison with the biphenyl compounds. The 4,4$\sp\prime$-isomer had only a mononitrene ESR signal, so a ground state singlet is assumed due to a superexchange mechanism between the paired electrons of oxygen and the $\pi$-electrons of the nitrenes. The 3,4$\sp\prime$-isomer showed very weak quintet signals, so a ground state quintet was assumed. The 3,3$\sp\prime$-isomer showed a very weak quintet signal, and a temperature study showed this to be an excited quintet state. Bis(4$\sp\prime$-nitrenophenyl)-1,3-butadiyne was generated for a study of the effect of acetylene as a coupling spacer. Its ESR spectra showed a strong mononitrene signal only and very weak signals presumed to be a quintet state. The spectrum suggests that this acetylene is a twisted structure where any coupling between nitrenes was changed from linear behavior.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-9006 |
| Date | 01 January 1994 |
| Creators | Minato, Masaki |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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