Direct detection of the axial conformer of methylcyclohexane by 63.1MHz carbon-13 nuclear magnetic resonance at low temperatures

Using 50.3 MHz 13C nmr at 173 K, distinct resonances for axial conformers of vinyl- and formylcyclohexane have been obtained. Substituent effects for axial and equatorial substitution of these groups have been derived. A deshielding γ–gauche effect was found for the axial substituent carbon of formylcyclohexane, a result attributed to the high preference for rotamers in which the formyl proton does not sterically interfere with syn-axial protons at C-3 and C-5 of the ring. Conformational free energies for the vinyl and formyl groups have been estimated to be 1.49 and 0.84 kcal/mol respectively.

Section: Data Insupporting

confidence: 85%

“…Among the early applications in the latter area was the work of Anet et al (1) in which the lowly populated axial conformer of methylcyclohexane was directly observed at 63.1 MHz.…”

Section: Introductionmentioning

confidence: 99%

Low temperature carbon-13 magnetic resonance detection of axial conformers in vinyl- and formylcyclohexane: a deshielding γ–gauche effect

Buchanan¹

1982

“…Early definitive work in this area with respect to "C NMR was carried out using monosubstituted compounds ( 1 4 ) . Consequently, axial and equatorial a , P, y , and 6 substituent effects have now been delineated for a wide variety of monosubstituted cyclohexane derivatives (1)(2)(3)(4)(5)(6)(7).…”

Section: Introductionmentioning

confidence: 99%

cis-Cyclohexano-9-crown-3 ether. Solid state and low-temperature solution stereochemistry as determined by X-ray crystallography and nuclear magnetic resonance spectroscopy

Buchanan¹,

Driega²,

Moghimi³

et al. 1993

The X-ray crystal structure of the title material has been determined at −130 °C. Low-temperature 1H1H COSY, 13C1H HETCOR, and DEPT 13C NMR spectra have been recorded, which permit unambiguous assignments of all carbon resonances when ring inversion is slow on the NMR timescale. The limiting low-temperature solution phase 13C spectrum has many common features with the solid phase 13C CPMAS spectrum recorded at 300 K. Spectra for the 7,10-tetra-deuterio derivative have also been obtained and substituent influences on 13C shieldings are discussed in detail.

“…These shifts, termed y effects, are consistently to higher field with increased steric crowding and, consequently, provide a new method for the assignment of stereochemistry in a variety of systems. The relative magnitudes of the shifts are well characterized for cyclohexane derivatives (2,3) in which, for example, an axial methyl carbon absorbs ca. 6 p.p.m.…”

mentioning

confidence: 99%

¹³C Nuclear Magnetic Resonance Studies. 32. The ¹³C Spectra of Several Norbornyl Derivatives

Stothers¹,

Tan²,

Teo³

1973

The 13C n.m.r. spectra of several norbornyl derivatives have been recorded to examine the variation of I3C shieldings with molecular geometry. Since it is well established that nonbonded interactions between vicinal carbon nuclei lead to pronounced upfield shifts, the so-called y effects, series of methyl-substituted norbornanes, norbornenes, norbornan-2-ones (norcamphors), and norborn-5-en-2-ones were prepared a s model systems having a variety of y interactions between vicinal methyl groups. The observed shifts of these methyl carbons are considered in terms of the dihedral angle relating the vicinal nuclei. The use of specific deuterationfor unequivocal signal assignments ofcarbons geminal and vicinal to the site of deuteration is illustrated.Les spectres 1.m.n. I3C de plusieurs derives du norbornyle ont ete enregistres afin d'etudier la variation de I'effet de blindage du I3C en fonction de la geometrie moleculaire. Puisqu'il est bien connu que d e s interactions non-likes entre des carbones vicinaux entrainent des deplacements du signal vers des champs Cleves, relation connue sous le nom effets-y plusieurs norbornanes, norbornenes, norbornanones-2 (norcamphres) et norbornkne-5 ones-2 substituis par des groupes methyles ont i t 6 prCpares afin de servir d e modkles posskdant diffkrentes interactions y entre des groupes methyles vicinaux. O n a utilis6 la deutCration spicifique pour attribuer sans arnbiguite les signaux se rattachant aux carbones gCmines et vicinaux au site d e deuteration.[Traduit par le journal]Can. J . Chem., 51, 2893Chem., 51, (1973