SCHEDULED MAINTENANCE
Effect of aromatic ring fluorination on CH⋯π interactions: microwave spectrum and structure of the 1,2-difluorobenzene⋯acetylene dimer†
Abstract
Rotational spectra for the normal isotopic species and for six additional isotopologues of the 1,2-difluorobenzene⋯acetylene (C6H4F2⋯HCCH) 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 benzene⋯acetylene dimers. In 1,2-difluorobenzene⋯HCCH, the H⋯π 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 fluorobenzene⋯HCCH complex. In addition, in 1,2-difluorobenzene⋯acetylene, 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 (benzene⋯HCCH) or nearly perpendicular (fluorobenzene⋯HCCH, ∼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 13C substituted isotopologues.
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