High electron affinities of bicyclo[n, n, 0]perfluoroalkanes

Abstract

Electron attachment is an important contributor to the chemistry of perfluoroalkanes. The adiabatic electron affinities (AEAs) and vertical electron affinities (VEAs) of bicyclo[n, n, 0]perfluoroalkanes (n, n-BCPFA) (where n= 1, 2, 3, 4) were computed using hybrid density functionals with DZP++ (polarization and diffuse function augmented double-ζ) basis sets. The bicyclo[1, 1, 0]perfluorobutane (1,1-BCPFA) and bicyclo[2, 2, 0]perfluoro-octane exhibit exceptionally high electron affinities for a saturated perfluoroalkane at all the levels of theory (2.20 and 1.86 eV, respectively; KMLYP/DZP++ with zero-point corrections). The predicted zero-point corrected AEAs of the n, n-BCPFAs range from 1.40 to 2.20 eV with the KMLYP/DZP++ level of theory. The structural changes which occur over the different ring sizes are varied and are dictated by the mode of electron binding by the n, n-BCPFA. Spin density and SOMO plots reveal that 1,1-BCPFA and 2,2-BCPFA bind the electron in a C–C antibonding σ* orbital. The 2,2-BCPFA radical anion has two minima differing in their nature of binding the ‘extra electron’. One of the minima has the electron distributed around the cleaved bridgehead C–C bond, and the other has it dispersed over the entire carbon skeleton. The 4,4- and 5,5-BCPFA radical anions hold the unpaired electron in a C–F antibonding σ* orbital which is localized on an exceptionally long tertiary C–F bond. The 1,1-BCPFA radical anion exhibits an exceptionally long bridgehead C–C bond. The most stable minimum of the 2,2-BCPFA radical anion exhibits similar characteristics as the 1,1-BCPFA radical anion. The 3,3-BCPFA (both the cis and trans forms) and the trans form of the 4,4-BCPFA radical anion display exceptionally long tertiary C–F bonds.