The Enantiomers of Indolino Spiro Compounds. Barriers to Thermal Cleavage of Their C(sp³)-O BOND*

Photo-, Thermo-, Solvato-, and Electrochromic Spiroheterocyclic Compounds

“…Another approach is based on the preparative separation or enrichment of the enantiomers of 1 and direct determination of the rate constants of thermal racemization. Resolution of spiropyrans of several types, 11 , 13a , and 14 , as well as spirooxazines 20 (X = N), with the use of chiral-phase HPLC on microcrystalline triacetyl- and tribenzoylcellulose has been accomplished for the first time by Mannschreck and co-workers, , who measured energy barriers to the ring opening by polarimetry and off-line or on-line circular dichroism (CD). The most representative data on the energy barriers of ring-opening reactions obtained with the use of NMR and chiroptical methods are collected in Tables −7.…”

Spirooxazines: synthesis, structure, spectral and photochromic properties

“…The tautomeric equilibrium between the cyclic A and merocyanine B forms in the ground state is typical of SPO in solutions. The A > B equilibrium was studied by 1 H NMR spectroscopy, 85,95,96 circular dichromism spectroscopy 164,165 and spectrophotometry. 13, 96, 166 ± 169 If the concentrations of the equilibrium forms A and B are sufficiently high that they can be reliably identified by NMR…”

Thermal Racemization of Substituted Indolinobenzospiropyrans: Evidence of Competing Polar and Nonpolar Mechanisms

“…Surprisingly, CD measurements have shown that 5 undergoes thermal racemization 10 times faster than 4 under the same conditions! 14 To explain this unusual result, we have investigated the effect of substituents on the rate of thermal racemization of the indolinobenzospiropyrans 1 and 6a − l using solvents that are less polar than those used in previous studies (vide supra). , In this paper, we report the measurements of rate constants for racemization ( k rac ) of 1 and 6a − l by CD spectropolarimetry in three different solvents and correlations of the k rac values with Hammett σ p and σ - constants. These results strongly suggest that the thermal racemization of indolinobenzospiropyrans proceeds via competing polar and nonpolar mechanisms, and that the outcome of this competition is a function of solvent polarity.…”

“…Mannschreck and co-workers resolved several spiropyrans and spirooxazines by chiral phase HPLC on microcrystalline triacetylcellulose and measured their Δ G ‡ inv by on-line circular dichroism (CD) using methanol and ethanol as solvents …”