title: Effect of aromatic ring fluorination on CHπ interactions: microwave spectrum and structure of the 1,2-difluorobenzeneacetylene dimer.
abstract: Rotational spectra for the normal isotopic species and for six additional isotopologues of the 1,2-difluorobenzeneacetylene (C6H4F2HCCH) weakly bound dimer have been assigned in the 6-18 GHz region using chirped-pulse Fourier-transform microwave spectroscopy. This is the third complex in a series of fluorinated benzeneacetylene dimers. In 1,2-difluorobenzeneHCCH, the Hπ distance (2.725(28) Å) is longer by about 0.23 Å, and the estimated binding energy (EB = 2.3(6) kJ mol(-1)) is weaker by about 1.8 kJ mol(-1), than in the previously studied fluorobenzeneHCCH complex. In addition, in 1,2-difluorobenzeneacetylene, HCCH tips ∼46(3)° away from perpendicular to the aromatic ring, with the H nearest the ring moving away from the fluorine atoms along the C2 axis of the monomer, while in the fluorobenzene and benzene complexes HCCH is perpendicular (benzeneHCCH) or nearly perpendicular (fluorobenzeneHCCH, ∼7° tilt) to the ring plane. Results from ab initio and DFT calculations will be compared to an experimental structure determined from rotational constants for the DCCD and five unique (13)C substituted isotopologues.
authors.affiliation: Department of Chemistry, Eastern Illinois University, 600 Lincoln Avenue, Charleston, IL 61920, USA. sapeebles@eiu.edu.
authors.forename: Anuradha G
authors.initials: AG
authors.lastname: Akmeemana
authors.forename: Justin M
authors.initials: JM
authors.lastname: Kang
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Dorris
authors.forename: Rebecca D
authors.initials: RD
authors.lastname: Nelson
authors.forename: Ashley M
authors.initials: AM
authors.lastname: Anderton
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Peebles
authors.forename: Sean A
authors.initials: SA
authors.lastname: Peebles
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Seifert
authors.forename: Brooks H
authors.initials: BH
authors.lastname: Pate