Enantiomerization Kinetics of 2,2′‐Disubstituted Biphenyls: A Dynamic Chiral HPLC Investigation

Abstract

The enantiomers of eight axially chiral biaryls were separated by chiral HPLC. On‐column enantiomerization of 1‐(o‐tolyl)naphthalene and 2‐cyclohexyl‐2′‐dimethylaminobiphenyl was observed between 10 °C and 35 °C, generating characteristic HPLC elution profiles with a plateau between the resolved enantiomer peaks. Computer simulation of the experimentally obtained chromatograms allowed determination of the Gibbs free energies of activation, ΔG≠, as 93.2 kJ/mol and 88.4 kJ/mol, respectively.

Phenylene‐Bridged Perylene Monoimides as Acceptors for Organic Solar Cells: A Study on the Structure–Property Relationship

“…The introduction of a methyl group on the phenyl linker increases the rotation barrier to 93 kJ mol −1 . This value is in excellent agreement with the experimentally obtained value for a naphthalene with an o ‐methylphenyl substituent (93 kJ mol −1 ) [36] . Thus, for compound 5 (and also compound 4 ) rotation around the C−C bond is expected to be possible at room temperature.…”

“…This value is in excellent agreement with the experimentally obtained value for a naphthalene with an o-methylphenyl substituent (93 kJ mol À 1 ). [36] Thus, for compound 5 (and also compound 4) rotation around the CÀ C bond is expected to be possible at room temperature. This could be confirmed by NOESY1D spectra in which a cross relaxation between the methyl protons and the aromatic protons of the linker, both in ortho position, with three perylene core protons could be seen for compound 5 (Figure S32).…”

Recent trends and applications in liquid‐phase chromatography enantioseparation of atropisomers

“…As biphenyl and its derivatives have found applications in enantioselective catalysis and, recently, as chirality chemosensors , Wolf and co‐workers separated the enantiomers of the eight axially chiral biaryls 22 – 29 (Fig. ) by chiral HPLC on Lux Cellulose‐4 (MP = hex, FR = 1.0 mL/min) and observed on‐column enantiomerization of 1‐( o ‐tolyl)naphthalene 27 and 2‐cyclohexyl‐2’‐dimethylaminobiphenyl 28 . In these cases, computer simulation of the experimentally observed elution profiles at various temperatures yielded Gibbs free energies of activation, Δ G ‡ , of 93.2 and 88.4 kJ/mol, respectively.…”

1,2,3- versus 1,2-Indeno Ring Fusions Influence Structure Property and Chirality of Corannulene Bowls

“…Racemic 4- rac was separated by preparative HPLC over chiral stationary phase to obtain 4a (first eluted, α D 25 + 1004 (CHCl 3 , c = 0.025)) and 4b (second eluted, α D 25 – 1009 (CHCl 3 , c = 0.024)). From enantiomerization kinetics, the bowl-inversion barrier was inferred to be 109.8 kJ/mol (CHCl 3 , 62 °C). , Thus, a level of configurational stability for 4 is established at about 2 h at 60 °C (over a day at ambient temperature). With configurationally stable enantiomers of 4 in hand, how can we best determine and assign the absolute configuration?…”

“…Racemic 4-rac was separated by preparative HPLC over chiral stationary phase to obtain 4a (first eluted, α D 25 + 1004 (CHCl 3 , c = 0.025)) and 4b (second eluted, α D 25 − 1009 (CHCl 3 , c = 0.024)). From enantiomerization kinetics, the bowl-inversion barrier was inferred to be 109.8 kJ/mol (CHCl 3 , 62 °C).…”