Concerning the internal rotational barrier and the experimental and theoretical ⁿJ(¹³C,¹³C) and ⁿJ (¹H,¹³C) in ethylbenzene-β-¹³C

Abstract

The 1H nuclear magnetic resonance spectra of ethylbenzene-β-13C in CS2/C6D12 and acetone-d6 solutions yield long-range 1H,1H and 1H,13C coupling constants. The 13C {1H} NMR spectra yield 13C, 13C couplings. The conformational dependence of some of these coupling constants is compatible with two values of the barrier to internal rotation about the exocyclic Csp2—Csp3 bond. If the fourfold component of the internal rotational potential is not larger than about 20% of the twofold component and the perpendicular conformer is most stable, then the barrier height is probably less than 6 kJ/mol. However, if the stable conformer has a torsion angle of 60° for the exocyclic C—C bond, then the coupling constants are consistent with a twofold barrier of about 23 kJ/mol. Experimental values of [Formula: see text] and [Formula: see text], where ψ and θ are the torsion angles for the exocyclic C—C and C—H bonds, respectively, are compared to those obtained from INDO MO FPT computations of the angular dependence of nJ(H,C), and nJ(H,H), nJ(C,C) for n ≥ 3. For example, the computations very likely give the correct qualitative ψ dependence of 5J(C,C), yet overestimate its extremum by about a factor of two, either because of an overestimate of the σ–π exchange integrals or because of too large a valence orbital density at the carbon nucleus. Other nJ values are discussed in a similar manner and, because optimized geometries are used in the computations, a somewhat more reliable treatment arises for some coupling constants; an example is 3J(C,C) at small torsion angles.

Effects of crystallinity of ZSM-5 zeolite on para-selective tert-butylation of ethylbenzene

“…The slight decrease in selectivity for 1,2-DEB from 200 to 400 °C was the result of increased steric hindrance for substitution at the ortho position as a result of free rotation of the ethyl group about the C-C bond. Such free rotation of alkyl groups in alkyl aromatics has been reported previously [38]. At low temperatures, the rotation would be slow, but at high temperatures it would be rapid, thus significantly suppressing substitution at both ortho positions.…”

Oxidation of Ethylbenzene to Acetophenone with N-Doped Graphene: Insight from Theory

“…For example, nitrogen-doped graphene could be used in a lot of different applications like electrochemical devices, field-effect transistors, ultracapacitors, biomedical sensors, and as a photocatalyst . The most studied application of doped graphene is its use as a catalyst for the oxygen reduction reaction (ORR) in fuel cells. − …”

Solid-State NMR Study of Guest Molecule Dynamics in 4-Alkyl-tert-butylbenzene/Thiourea Inclusion Compounds

“…Internal Rotation versus Molecular Rotation. Previous experimental and theoretical work on alkylbenzenes yields liquid- and gas-phase barriers to internal rotation for ethyl, isopropyl, and tert -butyl groups of 4−8, 1−9, and 2−5 kJ/mol, respectively. Evidently, these barriers are not sufficiently high that the alkyl groups can be considered as locked into one position with respect to the phenyl ring.…”