Modulating Electrostatic\nProperties and Noncovalent\nInteractions via Structural Isomerism: The Microwave Spectra and Molecular\nStructures of (<i>E</i>)- and (<i>Z</i>)‑1,2,3,3,3-Pentafluoropropene\nand Their Gas-Phase Heter

Microwave spectra of both the <i>E</i> and <i>Z</i> isomers of 1,2,3,3,3-pentafluoropropene along with all\nthree of\nthe singly substituted <sup>13</sup>C isotopologues for each are obtained\nusing broadband chirped-pulse Fourier transform microwave spectroscopy\nfrom 2.0–18.1 GHz. Associated quantum chemistry calculations\nshow that the barrier to internal rotation of the CF<sub>3</sub> group\nis significantly higher for the <i>Z</i> isomer, which is\nstabilized by an intramolecular hydrogen bond, although the barriers\nin both isomers are sufficiently high to prevent the observation of\nany effects due to internal rotation. The normal isotopologues of\nthe argon heterodimers for both isomers are also observed in the broadband\nspectrum and a Balle-Flygare cavity Fourier transform microwave spectrometer\nis used to obtain the 5.0–20.6 GHz spectra of the corresponding <sup>13</sup>C isotopologues. In each case, the argon atom locates so\nas to maximize its interactions with areas of significant electron\ndensity. However, mapped electrostatic potential surfaces indicate\nthat the areas of greatest nucleophilicity are different for the two\nisomers, suggesting that they may interact differently in forming\nheterodimers with protic acids.