Spectroscopy and reactivity of nitrene radical anions and nitrenes

Neloni Ranmali Wijeratine, Purdue University

Abstract

Nitrenes are unusual molecular structures that exhibit high reactivities. Although, they are isoelectronic with carbenes and can be generated and detected in a similar manner, they usually exhibit different reactivities. In this study we have used mass spectrometric methods and spectroscopy to determine thermochemical properties and reactivities of nitrene radical anions and nitrenes. Using ion chemistry in the flowing afterglow ion source we were able to measure enthalpy of formation and proton affinity of benzoylnitrene radical anion (BzN-). By combination of above measurements with other known properties we were able to calculate homolytic N-H bond dissociation energy of the benzamide in the gas phase for the first time. Additional thermochemical properties obtained include the electron affinity of benzamidyl radical, the hydrogen atom affinity of benzoylnitrene radical anion, and the oxygen anion affinity of benzonitrile. The reactivity studies carried out on BzN- turned out to be very interesting due to its open-shell nature. This allowed it to exhibit unique chemical reactivity with radical reagents and Lewis acids in the gas phase. We also found out that BzN- to be a useful reagent for the formation of ionized reactive intermediates, such as diradicals and carbenes. Although its reactivity is similar to that of O-, it can be used with substrates that are too acidic to give M-2H ions with O-. Therefore, it can be used to generate oxygen-based ions, such as ionized quinones and quinomethanes and the acetate radical that cannot be easily prepared by other methodologies. Spectroscopic studies of chloro and methoxy-substituted phenylnitrenes were carried out using a time-of-flight negative ion photoelectron spectrometer (NIPES) to determine how the introduction of substituents will affect their reactivity and thermochemical properties. The 355 nm photoelectron spectra of the substituted-nitrene anions are fairly similar to that measured for phenylnitrene anion (PhN-). Both have triplet ground states and open-shell structure for the low-lying singlet state, indicating they would exhibit the same reactivity as unsubstituted PhN. Furthermore. Electron affinities were measured for the above substituted phenylnitrenes and they are in excellent agreement with the values predicted by electronic structure calculations.

Degree

Ph.D.

Advisors

Wenthold, Purdue University.

Subject Area

Analytical chemistry|Organic chemistry|Physical chemistry

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