Application of carbon-13 nuclear magnetic resonance spectroscopy. 24. The spectra of cyclopropane-annelated bicyclo[2.2.2]octanes, three-membered-ring effects and chemical shift nonequivalence

Abstract

Experimental Section24Procedure. The reactions were conducted in the flow system previously described,2 but only with alumina catalyst F3 (Houdry HA-100, containing 0.4% sodium ion). Experiments 1-7 involved the use of 2-propanol as solvent and propylating agent. In expt 8 a solution of 2 g of phenol in 56 mL of benzene was added dropwise to the preconditioned catalyst while a mixture of nitrogen (33 mL/min)25 and propene (117 mL/min)25 was passed through the catalyst bed. Processing of the effluent as before gave 0.32 g of neutral, dark brown liquid. In expt 9-12 a solution of 6.9 g of substrate in 44 mL of benzene was added dropwise to the catalyst, but the gas stream consisted of nitrogen only. Product mixtures were collected as before2 and analyzed quantitatively by VPC at 150 °C (isothermally) on a 1 cm X 2.4 m column of

Orbital-Controlled Stereoselections in Sterically Unbiased Cyclic Systems

“…A cyclopropyl group is known to act as a strong π donor due to a high-lying occupied Walsh orbital, which is frequently regarded as an equivalent of a double bond. ,− Photoelectron spectra of the olefins 40a and 41a were previously measured and the signals assigned. ,− Vertical ionization potentials of the olefin π orbitals of 40a and 41a were found to be higher than those of the unsubstituted parent bicyclo[2.2.2]octene 35a (R 1 = R 2 = H) and 7-methylenenorbornane 28a (R 1 = R 2 = H), respectively, indicating a sizable interaction of the π orbital of the double bond with the occupied Walsh orbital of the fused cyclopropane ring. The previous account of the observed anti facial preference of 41a was based on this interaction, in particular, out-of-phase interaction of the relevant orbitals ( 4.36 ). − However, the corresponding out-of-phase interaction of the olefinic π orbital with the Walsh orbital of the cyclopropyl group ( 4.35 ) does not seem to be relevant to 40a because of the observed reverse syn preference.…”

“…154,156 A cyclopropyl group is known to act as a strong π donor due to a high-lying occupied Walsh orbital, 158 which is frequently regarded as an equivalent of a double bond. 154,[159][160][161][162][163][164][165][166] Photoelectron spectra of the olefins 40a and 41a were previously measured and the signals assigned. 154,[163][164][165][166] Vertical ionization potentials of the olefin π orbitals of 40a and 41a were found to be higher than those of the unsubstituted parent bicyclo[2.2.2]octene 35a (R 1 ) R 2 ) H) and 7-methylenenorbornane 28a (R 1 ) R 2 ) H), respectively, indicating a sizable interaction of the π orbital of the double bond with the occupied Walsh orbital of the fused cyclopropane ring.…”

Study of tyrosine and dopa enantiomers as tyrosinase substrates initiatingl‐ andd‐melanogenesis pathways

“…The 13C-NMR spectra of the l-tyrosine, dtyrosine, l-dopa, and d-dopa considered here were obtained in a Varian Unity spectrometer of 300 MHz [24,42]. The electronic density of a carbon atom is correlated with the value of its chemical displacement (δ) in 13 C-NMR [43,44]. Moreover, the nucleophilic power or electron-donating capacity of the oxygen atom of one phenolic hydroxyl has been seen to be inversely correlated with the δ value obtained in 13 C-NMR in the case of the carbon atom that binds to the hydroxyl group [45].…”