Microwave spectrum, structure and dipole moment of 3-fluorophenylacetylene (3FPA)

Abstract

The 6-18 GHz rotational spectrum of 3-fluorophenylacetylene (3FPA) was measured by chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy. Rotational constants and quartic centrifugal distortion constants based on a Watson-A reduction were determined with 89 transitions; A = 3383.73821(33) MHz, B = 1180.97617(16) MHz, C = 875.26172(12) MHz, ∆J = 0.0382(13) kHz, ∆K = 1.316(21) kHz, δJ = 13.93(56) Hz, and δK = 180.3(60) Hz. An additional 12-13 transitions for each of eight 13 C isotopic species and Stark effect to determine dipole moment components were observed by Balle-Flygare FTMW spectroscopy. Gas phase molecular structures of 3FPA were derived via the leastsquare fitting (r0) and substitution (rs) methods using the moments of inertia of the isotopic species. The ring geometry is discussed and compared with previous studies of structures of monosubstituted benzene and crystalline solid structures of 3FPA.

Microwave spectrum, structure and dipole moment of 4-fluorophenylacetylene (4FPA)

“…Thus, the sum of two values (2.04(3) D) is consistent with the experimental dipole moment of 4-fluorotoluene [36][37]. Furthermore, in the case of 3FPA, when the included angle between C−C≡C−H and C−F is supposed to be 120°, the result of vector summation is 1.45 D and it is in agreement with the experimental dipole moment, 1.361(1) [1].…”

“…Unlike the methyl group in toluene, the acetylenic group in phenylacetylene has not decreased the opposite angle significantly. The smaller C3C4C5 angle in 4FPA than fluorobenzene's, though the difference is only one degree, is particularly interesting since the fluorinated angle in 3FPA is comparable to that of fluorobenzene, 123.5° [1].…”

“…Using the 480 MHz bandwidth chirped-pulse FTMW, the 6-18 GHz spectrum of 4FPA was initially recorded. As it has C 2v symmetry, a smaller number of transitions was observed than for the previously studied 3FPA (3-fluorophenylacetylene) [1]. Further transitions out of the range of the CP-FTMW spectrometer for the normal isotopic species, and for all minor isotopic species, were measured by a standard resonant cavity FTMW.…”

“…There are three isomers of fluorophenylacetylenes that differ in the fluorine position relative to the acetylenic group: 2-fluorophenylacetylene (2FPA), 3-fluorophenylacetylene (3FPA), and 4-fluorophenylacetylene (4FPA). The meta-substituted compound, 3FPA, was already reported by our group using microwave spectroscopy [1]. The paper includes its spectrum, structure and dipole moment components.…”