Two-fold rotational barriers in 1,1,2,2-tetrasubstituted ethanes a dynamic nmr and molecular mechanics study of some highly-branched saturated hydrocarbons

Anderson, J. Edgar; Bettels, B.R.; Hoffmann, H. M. R.; Pauluth, Detlef; Hellmann, S.; Beckhaus, Hans‐Dieter; Rüchardt, Christoph

doi:10.1016/s0040-4020(01)86000-2

Cited by 11 publications

(5 citation statements)

References 35 publications

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“…Assignment of these conformers was performed with the aid of 1 H NMR NOE experiments. The conformational dynamics of 10 and similar amines significantly differ from those of trialkylamines with less bulky substituents , but more flexible moieties and that of the hydrocarbon 3-isopropyl-2,2,4,4-tetramethylpentane, i.e., 10 with CH instead of the N atom. Shorter C–N bonds in comparison with C–C bonds and underestimated steric congestion of tertiary amines may be relevant factors to provide an explanation.…”

Section: Results and Discussionmentioning

confidence: 98%

Steric Hindrance Underestimated: It is a Long, Long Way to Tri-tert-alkylamines

et al. 2018

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Ten different processes (Methods A-J) were tested to prepare tertiary amines bearing bulky alkyl groups. In particular, S1 alkylation of secondary amines with the help of 1-adamantyl triflate (Method D) and reaction of N-chlorodialkylamines with organometallic reagents (Method H), but also attack of the latter reagents at iminium salts, which were generated in situ by N-alkylation of imines (Method J), led to trialkylamines with unprecedented steric congestion. These products showed a restriction of the rotation about the C-N bond. Consequently, equilibration of rotamers was slow on the NMR time scale resulting in distinguishable sets of NMR data at room temperature. Furthermore, tertiary amines with bulky alkyl substituents underwent Hofmann-like elimination when heating in toluene to form an olefin and a secondary amine. Since the tendency to take part in this decay reaction correlated with the degree of steric hindrance around the nitrogen atom, Hofmann elimination at ambient temperature, which made the isolation of the tertiary amine difficult, was observed in special cases.

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Section: Results and Discussionmentioning

confidence: 98%

Steric Hindrance Underestimated: It is a Long, Long Way to Tri-tert-alkylamines

et al. 2018

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“…In conclusion, distinctive stereodynamic processes that involve the two enantiotopic substituents of a formally achiral molecule (e.g. diphenyl sulfoxide) can be observed only in situations where the anisotropic environment (in this case the crystal packing) renders the two groups symmetry nonequivalent, thus making the whole supramolecular system chiral; on the contrary this effect cannot be detected in achiral isotropic media, unless the formally achiral molecule adopts a chiral conformation 23…”

Section: Methodsmentioning

confidence: 93%

Unprecedented Detection of Distinct Barriers Involving Formally Enantiotopic Substituents: Phenyl Rotation in Solid Diphenyl Sulfoxide

Casarini

Lunazzi

Mazzanti

2001

Angew. Chem. Int. Ed.

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“…The dynamic behaviour of the highly hindered tri-tertbutylcarbinol (1) has been extensively studied by 1 H and 13 C NMR in solution and in the solid state. 1 -4 Molecular mechanics calculations have been performed to determine the rotational barriers of tert-butyl groups.…”

Section: Introductionmentioning

confidence: 99%

“…1 -4 Molecular mechanics calculations have been performed to determine the rotational barriers of tert-butyl groups. 1,4 The influence of the hydroxyl group on the 13 C chemical -shift values of aliphatic acyclic alcohols has been well established. 5 In a related 17 O NMR study of sterically hindered aliphatic alcohols, intramolecular through-space interaction of the -methyl hydrogen with the oxygen lone pair has been reported.…”

Section: Introductionmentioning

confidence: 99%

Dynamic NMR study of tri-tert-butylcarbinol and of a carbinol-methylaluminoxane mixture

Helaja

Hakala²,

Helaja

et al. 2000

Magn. Reson. Chem.

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The reaction of tri‐tert‐butylcarbinol and oligomeric methylaluminoxane (MAO) prepared in toluene‐d8 was studied by analysing the reaction mixture utilizing ROESY, HSQC and HMBC 2D NMR experiments. The formation of one main alkoxide was observed in the reaction. Dynamic 13C NMR and semiempirical PM3 molecular modelling were used in concert to study the tert‐butyl group rotation barriers of this alkoxide. From several modelled acyclic and cyclic MAO fragments, an open chain—Al(Me)OAl(Me)—fragment was observed to be consistent with the NMR results. Copyright © 2000 John Wiley & Sons, Ltd.

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Two-fold rotational barriers in 1,1,2,2-tetrasubstituted ethanes a dynamic nmr and molecular mechanics study of some highly-branched saturated hydrocarbons

Cited by 11 publications

References 35 publications

Steric Hindrance Underestimated: It is a Long, Long Way to Tri-tert-alkylamines

Steric Hindrance Underestimated: It is a Long, Long Way to Tri-tert-alkylamines

Unprecedented Detection of Distinct Barriers Involving Formally Enantiotopic Substituents: Phenyl Rotation in Solid Diphenyl Sulfoxide

Dynamic NMR study of tri-tert-butylcarbinol and of a carbinol-methylaluminoxane mixture

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