The conformational properties of some phenyl esters. Molecular orbital and nuclear magnetic resonance studies

Abstract

. Can. J. Chem. 65, 2175 (1987). Extensive, geometry-optimized, STO-3G MO computations on phenyl formate imply a strongly nonplanar Z conformer (C=O bond cis to the phenyl group) at ambient temperatures. The internal barrier to rotation about the C(1)-0 bond in this conformer is computed as v/k~mol-' = (-5.17 * 0.27) sin2 0 -(2.42 k 0.27) sin2 20, 0 being zero for the planar conformer; the twofold is nearly twice as large as the fourfold component. The expectation value of 0 is 58" at 300 K. The spin-spin coupling constants over six bonds between I3C and I9F nuclei in 4-fluorophenyl formate, acetate, propionate, and isobutyrate, as well as in the 2,6-dichloro-4-fluorophenyl acetate, are adduced as evidence for nonplanar conformers of these molecules. The magnitudes of these six-bond coupling constants are consistent with internal barriers to rotation about the C(1)-0 bonds, which are similar in magnitude to those given by the computations on the Z conformer of phenyl formate. The energies of the planar and nonplanar E conformers, as well as the interconversion energies for E = Z isomerization, are computed. Small amounts of the nonplanar E conformer are predicted at ambient temperatures. The I3C chemical shifts and the one-bond 13C, I9F coupling constants are consistent, respectively, with only minor variations in the conformational behavior of the ester moieties caused by the fluorine substituent and by changes in the structures of these moieties themselves.TED SCHAEFER et GLENN H. PENNER. Can. J. Chem. 65, 2175 (1987). Des calculs ktendus d'OM effectuks au niveau STO-3G sur du formate de phknyle optimisC pour la gkomktrie laissent fortement supposer que le conformkre Z non-plan (la liaison C=O est cis par rapport au groupement phknyle) est privilCgiC B la tempkrature ambiante. On a calculC que la barrikre interne B la rotation autour de la liaison C(1)-0 de ce conformtre peut &tre exprimCe par 1'Cquation V/kJ mol-I = (-5,17 * 0,27) sin2 0 -(2,42 ? 0,27) sin2 20 dans laquelle 0 : st Cgal B zCro pour le conformtre plan; la composante binaire est deux fois plus importante que la composante quaternaire. A 300 K , la valeur attendue pour 0 est de 58". On a aussi utilisC les constantes de couplage spin-spin a travers six liaisons entre les noyaux de I3C et de I9F des formate, acetate, propionate et isobutyrate de fluoro-4 phCnyle de mCme que de 1'acCtate du dichloro-2,6 fluoro-4 phtnyle comme preuve de l'existence des conformkres non-plans de ces molCcules. Les amplitudes de ces constantes de couplage B travers six liaisons sont en accord avec des barritres 1 la rotation autour des liaisons C(1)-0 qui sont semblables en amplitude B celles obtenues par calculs sur la conformkre Z du formate de phCnyle. On a aussi calculC. les Cnergies des conformtres E plan et non-plan ainsi que les Cnergies d'interconversion pour 1'isomCrisation E = Z. A la tempkrature arnbiante, on prCdit que de faibles proportions du conformkre E non-lan existeront. Le dCplacements chimiques en rksonance ! magnktique nuclkaire du I3C et les consta...

Why (1S)-Camphanates Are Excellent Resolving Agents for Helicen-1-ols and Why They Can Be Used to Analyze Absolute Configurations

“…The figure shows that the carbonyl groups of phenol esters do not lie in the planes of the benzene rings. Instead, the preferred angles a are 92 ± 26° and −90 ± 27°, in accord with previous NMR spectroscopic and theoretical analyses. , Steric repulsions between the carbonyl oxygens and the phenyl's C-2 hydrogens are thought to be the determinants. , Thus in 5 , the CO bond must point either down, toward the aromatic rings at the other end of the helicene, or up, away from the helicene framework. Both space-filling models and calculations to be described below, using the MacroModel molecular mechanics program with the MM3* force field, imply that the preferred orientation should be the latter, in which the carbonyl points away from the helicene framework.…”

Extrapolative prediction using physically-based QSAR

“…The corresponding 3D overlay with the most similar training ligand (which was a phenyl methyl sulfone) shows ChEMBL318881 with the 4-fluorophenyl ester group both non-planar and in the E conformation. Although this may not be the lowest energy state, this conformation of a 4-fluorophenyl alkyl ester is not unreasonable [ 41 ].

Fig.

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Resolution of a Configurationally Stable Hetero[4]helicene

“…Regardless, all chiral acids 7a-h (Scheme 5 panel A and Table 1) allowed the formation of diastereomeric esters 8a(a-h) (Scheme 5 panel A and Table 1) in good yields, in none of these cases it was possible to separate the diastereoisomeric mixtures by flash chromatography or crystallization. We thought, as suggested by literature data [25][26][27][28][29][30][31][32][33][34][35][36][37][38], that functionalization of the cape-zone position keeps the chiral auxiliaries too far from the superimposition area of the terminal aryl rings vanishing separation. Thus, we moved to helicene 1b(OH), which allowed for the insertion of chiral auxiliaries on 1-position, ortho to the nitrogen atom, which we indicated as bay-zone, i.e., exactly in the area of terminal ring superimposition (Scheme 5B).…”

“…We thought, as suggested by literature data [25][26][27][28][29][30][31][32][33][34][35][36][37][38], that functionalization of the capezone position keeps the chiral auxiliaries too far from the superimposition area of the terminal aryl rings vanishing separation. Thus, we moved to helicene 1b(OH), which allowed for the insertion of chiral auxiliaries on 1-position, ortho to the nitrogen atom, which we indicated as bay-zone, i.e., exactly in the area of terminal ring superimposition (Scheme 5B).…”