The intramolecular equilibrium in 2-tert-butylphenol and some derivatives. An anomalous indicating steric distortion

Abstract

. Can. J. Chem. 62, 113 (1984). The 'H nmr spectral parameters in dilute carbon tetrachloride solution arc reported for 2-tert-butylphenol, as obtained by decoupling of the sidechain protons. Long-range couplings between hydroxyl and ring protons are also reported for five derivatives of 2-terr-butylphenol. In the cis conformer of 2-tert-butylphenol an anomalous ' J ? '~- ' occurs, most likely as a consequence of a significant distortion of the COH geometry. Such an anomaly, which leads to an incorrect estimate of the cis-trans equilibrium constant, does not occur in other alkyl phenols, for example, in 2-tert-butyl-6-methylphenol. The coupling constant data provide no evidence for out-of-plane conformational preferences of the hydroxyl group in these compounds.TED SCHAEFER, RUDY SEBASTIAN et SALMAN R. SALMAN. Can. J. Chem. 62, 113 (1984). On rapporte les paramktres spectraux en rmn du 'H obtenus en dkcouplant les protons de la chaine lattrale du tert-butyl-2 phenol en solution dans le tttrachlorure de carbone. On rapporte Cgalement les couplages B longue distance entre le groupe hydroxyle et les protons du cycle de cinq dtrivCs du tert-butyl-2 phtnol. Dans le conformkre cis du tert-butyl-2 phtnol, il se produit un 5~: H ' H -5 anomal qui serait une consCquence d'une dtformation importante de la gComCtrie du groupe COH. Une telle anomalie, qui conduit B une tvaluation incorrecte de la constante d'tquilibre cis-trar~s, ne se produit pas dans les autres phCnols alkylCs: comme par exemple avec le tert-butyl-2 mCthyl-6 phCnol. Les donnCes de constante de couplage n'apportent pas la preuve d'une prCfCrence conformationnelle hors du plan du groupe hydroxyle de ces composts.[Traduit par le journal]

Concerning in 2-methylphenol and its derivatives. A proximate coupling

“…Furthermore, because 'J,!.OH has not been observed in any of the other phenol derivatives mentioned below, the discussion for all of them assumes cis-trans equilibria of planar conformations. As summarized previously ( 17), a variety of physical methods are all consistent with c o~l a n a r conformations of the hydroxyl group even in a highly hindered molecule like 2,6-di-tert-butylphenol. Again, the spin-spin coupling data on 2-isopropyl-6-methylphenol (16) are consistent with correlated conformations of the hydroxyl and isopropyl groups and no nonplanar conformations of the hydroxyl moiety were needed to interpret the experimental results.…”

“…This discrepancy can be rationalized. A substantial distortion of the geometry at the hydroxyl group is indicated by other spin-spin couplings in 2-tert-butylphenol, but must be rather less severe in 2-tert-butyl-6-methylphenol (17). As argued below, because 'J,.…”

“…J a trans b cis must also be very small in 2-allyl-6-methylphenol (1 1). Yet it clearly exists in 2-isopropyl-6-methylphenol (16), and in 2-tert-butyl-6-methylphenol 'J is -220 t 20 mHz (17). An interpretation of this apparent inconsistency is reached as follows.…”

A proton spin-lattice relaxation pathway analysis of conformational preferences of aryl and enol ethers in some cinchona and morphine alkaloids

“…Nuclear magnetic resonance (nrnr) has proven to be a very powerful technique for determination of the conformational bias of enols (6) and en01 ethers (3)(4)(5)7). Using a method that is closely related to techniques utilizing 'H{'H) nuclear Overhauser effects (nOe) (8), as reported by Sanders and co-workers (9) and Kruse et al ( 3 , the spin-lattice relaxation of vinylic, allylic, and ring protons of en01 and aromatic ethers in some cinchona and morphine alkaloids2 has been examined to gain insight into specific conformational preferences of the ether function.…”

1H nuclear magnetic resonance and molecular orbital studies of 2-formylstyrene. Three significant nonplanar conformers at 300 K

“…A speculative mechanism invokes the through-space, or proximate, interaction between the P-CH and the ortho C-H bonds, postulated for styrene (2). In all known cases (2,(35)(36)(37)(38)(39)(40)(41)(42) such an interaction leads to a negative coupling constant between the protons, as indicated in C by the parallel crossed arrows for H-6 and , CHO C H-8. Schematically, the repulsive overlap of the 1s orbitals centered on these protons is consistent with a parallel-spin preference of the electrons in these orbitals.…”