Effect of aromatic ring fluorination on CH⋯π interactions: microwave spectrum and structure of the 1, 2-difluorobenzene⋯acetylene dimer. Issue 35 (17th August 2016)

• Record Type: Journal Article
• Authors: Akmeemana, Anuradha G.; Kang, Justin M.; Dorris, Rachel E.; Nelson, Rebecca D.; Anderton, Ashley M.; Peebles, Rebecca A.; Peebles, Sean A.; Seifert, Nathan A.; Pate, Brooks H.
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 35(2016)
• Page Start: 24290
• Page End: 24298
• Publication Date: 2016-08-17
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp04737h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The H⋯π distance increases in o -C6 H4 F2 ⋯HCCH, compared to C6 H5 F⋯HCCH or C6 H6 ⋯HCCH, consistent with weaker interactions with increased ring fluorination. Abstract : Rotational spectra for the normal isotopic species and for six additional isotopologues of the 1, 2-difluorobenzene⋯acetylene (C6 H4 F2 ⋯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 ( E B = 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 C 2 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 13 C substituted isotopologues.