An experimental and theoretical investigation of the internal rotation in anisole

Konschin, Henrik; Tylli, Henrik; Grundfelt-Forsius, C.

doi:10.1016/0022-2860(81)85266-0

Cited by 64 publications

(16 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The state dependence of the rotational motion about the C ( 1 W bond is also suggested by ab initio molecular orbital calculations on the free molecule (13)(14)(15)(16)(17)(18), which have the barrier as less than 8 kJ/mol, as do molecular mechanics computations (19). Microwave spectra (3) agree that 1 is the structure in the gas phase, while for 4-fluoroanisole such spectra (20) are consistent with a lower limit to the barrier of 4.6 kJ/mol.…”

Section: Introductionmentioning

confidence: 84%

Long-range ¹³C, ¹³C spin–spin coupling constants in anisole and some derivatives

Schaefer¹,

Penner²

1988

Can. J. Chem.

View full text Add to dashboard Cite

13C nuclear magnetic resonance chemical shifts and nJ(13C,13C) are reported for anisole and 16 of its derivatives, all enriched with 13C in the methoxyl group. 5J(13C,13C) is directly proportional to sin2θ, where θ is the angle by which the methoxy group twists about the C(1)—O bond. In acetone-d6 solution, 5J(C,C) is not observable for a number of 4-substituted anisoles, except for 1,4-dimethoxybenzene. For the latter, 5J(C,C) is compatible with a twofold barrier of 19.3 ± 1.1 kJ/mol hindering rotation about the C(1)—O bond. However, it is unlikely that the barrier is purely twofold in nature. The observed 5J(C,C) is also compatible with 10.5 and 6.0 kJ/mol for the twofold and fourfold components, respectively, implying a dynamical nuclear magnetic resonance barrier of less than 13 kJ/mol. While phase and solvent effects on the internal barrier in anisole are certainly substantial, it appears that a fourfold component must also be present. The apparent twofold barrier in 2,6-difluoroanisole is 5.4 ± 0.9 kJ/mol, based on 5J(C,C) and 6J(H-4,13C). The latter coupling constant is also reported for 1,2,3-trimethoxybenzene and used to deduce its conformation. The θ dependence of 3J(C,C) and 4J(C,C) is briefly discussed for symmetrical anisole derivatives. Differential 13C, 13C isotope shifts are reported for 1,4-dimethoxybenzene.

show abstract

Section: Introductionmentioning

confidence: 84%

Long-range ¹³C, ¹³C spin–spin coupling constants in anisole and some derivatives

Schaefer¹,

Penner²

1988

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…The methyl groups, whose torsion angles were refined, are oriented to match the requirements of molecular C s symmetry and to exhibit a minimum steric repulsion with the ortho-H atoms of the benzene rings. Thus, the molecular structure of (I) encountered in the crystal appears to represent the minimum energy conformation (Seip & Seip, 1973;Konschin et al, 1981).…”

Section: Resultsmentioning

confidence: 99%

Anisole at 100 K: the first crystal structure determination

Seidel

Goddard

2015

Acta Crystallogr C

View full text Add to dashboard Cite

The simplest alkyl aryl ether, anisole (methoxybenzene), C7H8O, is a feedstock chemical and is widely used in the pharmaceutical industry. The structure of anisole at 100 K, as determined by single-crystal X-ray analysis, is reported. A crystal (m.p. 236 K) suitable for X-ray diffraction was obtained from the melt. The title compound crystallizes in the centrosymmetric space group P2(1)/c with two molecules in the asymmetric unit (Z' = 2). Both crystallographically distinct molecules adopt a virtually flat (Cs-symmetric) conformation. The arrangement of the molecules in the solid state appears to be governed by close packing. No face-to-face π-π stacking of the molecules is observed, but rather edge-to-face interactions result in a herringbone packing motif.

show abstract

“…Qualitatively, therefore, the increased, computed rotational barrier in 3fluoroanisole is very likely correct. Of course, the internal barrier in anisole is state dependent (18)(19)(20) and, although its value in the vapor, as well as in solution, is unknown, there is little doubt that it is substantially higher in solution than in the gas phase or than the value computed (20). By way of contrast, the onefold component computed for 3-fluoroanisole, that is, the energy difference of 0.46 kJ/mol between the two planar conformers, happens to agree with that obtainable from the 'J(H,OCH~) values in CS2 and in acetone-d6 solutions.…”

Section: Molecular Orbital Resultsmentioning

confidence: 99%

¹H nuclear magnetic resonance and molecular orbital studies of the conformations of 3-fluoroanisole

Schaefer¹,

Sebastian²

1989

Can. J. Chem.

View full text Add to dashboard Cite

The proximate spin–spin coupling constant between the methyl protons and the ring protons, 5J(H,OCH3), is extracted from a full analysis of the 1H and 19F nuclear magnetic resonance spectra of 3-fluoroanisole in CS2 and acetone-d6 solutions. The values of 5J(H,OCH3) imply that the less polar cis conformer is slightly more stable at 300 K than the more polar trans conformer in both solvents, in agreement with geometry-optimized STO-3G MO computations for the free molecule. The latter also find a higher barrier to internal rotation of the methoxy group for 3-fluoroanisole than for the parent molecule. The present results are compared with other measurements of the conformer ratio for the vapor and for solutions. The STO-3G and 6-31G structures of the cis and trans conformers are compared. The C—F bond length is computed more reliably with the minimal basis set, as is the COC bond angle. The internal angles of the benzene moiety are, of course, found more accurately with the 6-31G basis. The computations indicate additivity of the substituent effects on the internal angle, as found experimentally for a variety of benzene derivatives. Keywords: 1H NMR of fluoroanisole, conformations of fluoroanisole, molecular orbital calculations for fluoroanisole.

show abstract

An experimental and theoretical investigation of the internal rotation in anisole

Cited by 64 publications

References 34 publications

Long-range ¹³C, ¹³C spin–spin coupling constants in anisole and some derivatives

Long-range ¹³C, ¹³C spin–spin coupling constants in anisole and some derivatives

Anisole at 100 K: the first crystal structure determination

¹H nuclear magnetic resonance and molecular orbital studies of the conformations of 3-fluoroanisole

Contact Info

Product

Resources

About

An experimental and theoretical investigation of the internal rotation in anisole

Cited by 64 publications

References 34 publications

Long-range 13C, 13C spin–spin coupling constants in anisole and some derivatives

Long-range 13C, 13C spin–spin coupling constants in anisole and some derivatives

Anisole at 100 K: the first crystal structure determination

1H nuclear magnetic resonance and molecular orbital studies of the conformations of 3-fluoroanisole

Contact Info

Product

Resources

About

Long-range ¹³C, ¹³C spin–spin coupling constants in anisole and some derivatives

Long-range ¹³C, ¹³C spin–spin coupling constants in anisole and some derivatives

¹H nuclear magnetic resonance and molecular orbital studies of the conformations of 3-fluoroanisole