title: Synthesis, chiroptical properties and density functional theory calculations of 3,3'-biphenyl-2,2'-bitropone.
abstract: The synthesis of new bitropone derivatives, namely, 3,3'-biphenyl-2,2'-bitropone and 7,7'-biphenyl-2,2'-bitropone, are reported. Isolation of enantiomers arising from restricted rotation around the C-C bond connecting the tropone moieties was attempted by means of chiral high performance liquid chromatography (HPLC). No separation was obtained for 7,7'-biphenyl-2,2'-bitropone. For 3,3'-biphenyl-2,2'-bitropone, difficulties were encountered because of the low separation factor of the peaks and the presence of a rapid racemization process. However, quantitative chiroptical data on the antipodes were obtained by linking a circular dichroism (CD) spectrometer and a UV-vis spectrophotometric detector in series to the HPLC instrument. The analysis of the CD and UV-vis spectra in terms of absolute conformations was done with the help of theoretical calculations performed at the Density Functional Theory (DFT) level. The most stable conformations of the 3,3'-biphenyl-2,2'-bitropone in its ground state were obtained. Starting from these minimum energy conformations, it was possible to compute theoretical CD and UV absorption spectra that fit well with the experimental ones. From this comparison the absolute configuration to the antipodes was assigned. Finally, the effect of the presence of the two lateral phenyl substituents on the structure of the bitropone and hence on the CD spectrum is discussed.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, via Risorgimento 35, 56126 Pisa, Italy.
authors.forename: Marino
authors.initials: M
authors.lastname: Cavazza
authors.forename: Mario
authors.initials: M
authors.lastname: Cifelli
authors.forename: Valentina
authors.initials: V
authors.lastname: Domenici
authors.forename: Tiziana
authors.initials: T
authors.lastname: Funaioli
authors.forename: Benedetta
authors.initials: B
authors.lastname: Mennucci
authors.forename: Carlo Alberto
authors.initials: CA
authors.lastname: Veracini
authors.forename: Maurizio
authors.initials: M
authors.lastname: Zandomeneghi
mesh_terms: D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D015394:Molecular Structure; D011789:Quantum Theory; D013237:Stereoisomerism; D014334:Tropolone / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: C587584:3,3'-biphenyl-2,2'-bitropone; D014334:Tropolone
keywords: CD; DFT; HPLC; UV-vis; atropoisomerism; enantiomers; separation, racemization; tropone