CF₃: an overlooked chromophore in VCD spectra. A review of recent applications in structural determination

Abstract

VCD allows one to investigate the configuration of stereogenic centers bearing a CF3-group and to define its interactions with nearby chemical groups.

π‐Extended Helical Nanographenes: Synthesis and Photophysical Properties of Naphtho[1,2‐a]pyrenes**

“…The trifluoromethyl functionalization of compounds 1 e , 1 f , and 1 i is evidenced by the similar spectral features in the box 11 region. Remarkably, the different location of the functionalization found in 1 i (R 2 ) vs 1 e and 1 f (R 1 ) is evidenced by the shift of the CF 3 signals from box 6 to box 7, respectively [21] . Finally, the functionalization by the methoxy group in compounds 1 c , 1 b , 1 g , 1 f , and 1 d is confirmed by the characteristic peak identified by boxes 12 and 13.…”

“…Remarkably, the different location of the functionalization found in 1 i (R 2 ) vs 1 e and 1 f (R 1 ) is evidenced by the shift of the CF 3 signals from box 6 to box 7, respectively. [21] Finally, the functionalization by the methoxy group in compounds 1 c, 1 b, 1 g, 1 f, and 1 d is confirmed by the characteristic peak identified by boxes 12 and 13. Interestingly, as documented by the tables found in Supporting Information, it is not possible to find a single IR marker of the nanographene core.…”

Structural characterization and antimicrobial activity of 2-[4,6-(Cl/CH3/CF3)-benzimidazol-2-yl]-4-(OCH3/Br)-phenols and their Zn(II), Pd(II) and Au(III) complexes

“…Aliphatic C-F bonds (CF3) present in HL3 and HL6 were observed as intense bands between 1060 and 1150 cm −1 . 28 The remarkable changes in complex compounds compared to ligands are as follows: Due to the coordination over C=N nitrogen and OH oxygen atoms in the complexes, the disappearance of OH bands around 3200 cm −1 and significant changes in the frequency and character of the C=N bands were observed. The coordination of imine nitrogen atom could also be confirmed by appearance of new bands with medium absorption around 620 and 690 cm −1 may be assignable to ν(M-N) vibration modes.…”

Helicity control of a perfluorinated carbon chain within a chiral supramolecular cage monitored by VCD

“…One may associate the intense doublet at 1370 cm −1 to carboxylate symmetric stretchings: the high energy component is attributed to the in phase vibrational modes in the two moieties; the low energy component receives contributions from out of phase symmetric carboxylate stretchings ( PP – P, MP – P, MP – M and MM – M ) while for MM – P and PP – M the low energy component of the doublet receives contributions prevalently from vibrations localized on the cage. The CF stretching bands at 1100–1190 cm −1 are less diagnostic for two main reasons: they are located in the lowest accessible spectroscopic range 5,19 and also aromatic CH bendings of the cage and CH 2 vibrations of the chiral cyclohexane ring are present there. Overall, considering observed versus calculated VCD features, we may notice that the doublet attributed to the guest appears quite intense and sharp as suggested by calculations, on the contrary, VCD bands due to vibrations of the cage, particularly the ones associated to the lateral chains, are broader and weaker.…”