Remarks on the internal motion in diphenyl ether. Fluorophenyl ethers

Abstract

and POTLAKI TSEKI. Can. J. Chem. 66, 1647Chem. 66, (1988. The I3C nuclear magnetic resonance chemical shifts and the I3C,l9F spin-spin coupling constants are reported for 4,4'-difluorophenyl ether and 4-fluorophenyl phenyl ether in CS, and in acetone-d6 solutions. An estimate of 6~9 0 , the extremum in the a-T coupling constant between the I9F nucleus on one ring and the ips0 I3c nucleus on the other, is obtained from measurements on 2,6-dibromo-4-fluorophenyl phenyl ether. The ensuing estimates of (sin' 0), the expectation values of sin2 0 as obtained from 6~( 1 3 C , 1 9~) , are compared with those obtained from STO-3G MO computations for diphenyl ether and its 4-fluoro derivatives. These computations give conformational energies at 30" intervals of the angles of twist about the two C-0 bonds. In rough agreement with C-INDO computations, interconversion of the helical forms is calculated to occur most easily by the so-called one-ring flip mechanism; the barrier to interconversion is less than 1 kJ/mol in the ether and its 4-fluoro derivatives. It appears that the conformational behaviour of these derivatives is unaltered by passage from CSZ to acetone solutions at 300 K. Furthermore, (sin' 0) values from 6~( 1 3~, 1 9~) in solution are very similar to those obtained from the computations on the free molecules. If this agreement is not accidental, then it may arise from a high degree of flexibility of the molecules in which, by a disrotatory or one-ring flip mechanism requiring a very low energy of activation, one helical or C2 conformation can be converted to another. The other conformations have considerably higher energies and the solvents do not appear to lower these energies enough to favor their populations significantly at 300 K. [Traduit par la revue]

NMR spectra of the porphyrins. Part 39. Paramagnetic shifts in cobalt(II) porphyrins

“…Consequently, we used the value 115", which is the average of this range but which has also been optimized by previous ab initio studies . 29 The proton paramagnetic shifts used in the optimization were those of the ortho-, meta-and parahydrogens on the second phenyl ring. Values for the first phenyl ring, which is the phenyl group directly attached to the porphyrin macrocycle, were not considered as this ring had already been optimized at 65" to the porphyrin plane.…”

Receptor interactions by polybrominated diphenyl ethers versus polychlorinated biphenyls: A theoretical structure–activity assessment

“…A variety of experimental and theoretical studies have shown that the unsubstituted diphenyl ether itself has a twist conformation in that φ1 and φ2 lie in the vicinity of 25-50° (Schaefer et al, 1988). In general, PBDE congeners prefer a skew or twist conformation depending on the number of the ortho-bromo substituents (Klösener et al, 2008).…”

Conformational flexibility of xanthene‐based covalently linked dimers

“…A variety of experimental and theoretical studies have been conducted on diphenyl ether and its derivatives in order to gain insights of internal dynamics of molecule. Those studies suggest that the unsubstituted diphenyl ether freely rotates in solution with barrier for rotation less than 1 kcal/mol . Introducing substituents in ortho position of diphenyl ether can significantly increase the energy barrier .…”