Rotation Of Tert-butyl Groups Research Articles

Solid-Solid Phase Transitions and tert-Butyl and Methyl Group Rotation in an Organic Solid: X-ray Diffractometry, Differential Scanning Calorimetry, and Solid-State 1H Nuclear Spin Relaxation.

Using solid-state 1H nuclear magnetic resonance (NMR) spin-lattice relaxation experiments, we have investigated the effects of several solid-solid phase transitions on tert-butyl and methyl group rotation in solid 1,3,5-tri-tert-butylbenzene. The goal is to relate the dynamics of the tert-butyl groups and their constituent methyl groups to properties of the solid determined using single-crystal X-ray diffraction and differential scanning calorimetry (DSC). On cooling, the DSC experiments see a first-order, solid-solid phase transition at either 268 or 155 K (but not both) depending on thermal history. The 155 K transition (on cooling) is identified by single-crystal X-ray diffraction to be one from a monoclinic phase (above 155 K), where the tert-butyl groups are disordered (that is, with a rotational 6-fold intermolecular potential dominating), to a triclinic phase (below 155 K), where the tert-butyl groups are ordered (that is, with a rotational 3-fold intermolecular potential dominating). This transition shows very different DSC scans when both a 4.7 mg polycrystalline sample and a 19 mg powder sample are used. The 1H spin-lattice relaxation experiments with a much larger 0.7 g sample are very complicated and, depending on thermal history, can show hysteresis effects over many hours and over very large temperature ranges. In the high-temperature monoclinic phase, the tert-butyl groups rotate with NMR activation energies (closely related to rotational barriers) in the 17-23 kJ mol-1 range, and the constituent methyl groups rotate with NMR activation energies in the 7-12 kJ mol-1 range. In the low-temperature triclinic phase, the rotations of the tert-butyl groups and their methyl groups in the aromatic plane are quenched (on the NMR time scale). The two out-of-plane methyl groups in the tert-butyl groups are rotating with activation energies in the 5-11 kJ mol-1 range.

A quantum chemical study of the structure and energy of β-diketonates. XVII. Internal rotation of radical substituents in β-diketonate molecules

A quantum chemical study of the internal rotation of CX3 (X = H, F, CH3) radical substituents in scandium and calcium β-diketonate complexes is performed. Calculations are carried out using the GAUSSIAN-03 program at the HF and DFT/B3LYP levels with relativistic effective core pseudo-potentials and valence double zeta basis sets. Analytical expressions V(φ) are obtained that describe the potential energy variation during the rotation of CX3 groups. The rotation of CH3 and CF3 groups is shown to be described by a simple potential of the form V = V0/2 + V3cos(3φ), while for the description of the rotation of tert-butyl groups it is required to use a more complex function V = V0/2 + V3cos(3φ) + V6cos(6φ). Based on the obtained expressions for V(φ), the effective torsion angles φef of the rotation of CX3 groups are calculated for different temperatures. It is shown that φef obtained based on the quantum chemical calculations are close to the values obtained in electron diffraction experiments.

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

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.

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

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.

Internal Rotation and Butterfly-like Ring Inversion in 9-tert-Butylanthracene

In the solid state 9-tert-butylanthracene exists in a structure where the anthracene ring is nonplanar. The dihedral angle between the two lateral benzenic rings is about 18°. In addition the tertiary butyl group is displaced in a direction opposite to the ring bending. Ab initio molecular orbital calculations (3-21G) agree that the isolated (gas phase) molecule exists in a nonplanar geometry and indicate that there are two mechanisms for tert-butyl group rotation. A high-energy (35.1 kJ/mol) rotation requires a further bending of the tert-butyl group. The low-energy process (4.7 kJ/mol) involves a concerted tert-butyl rotation and butterfly-like inversion (flapping) of the anthracene fused ring. The motion of the tert-butyl group in solid 9-tert-butylanthracene was monitored by variable temperature 13C CP/MAS NMR spectroscopy and appears to follow the high-energy mechanism for tert-butyl rotation with an activation energy of 63.1 ± 2.7 kJ/mol. The nearly 30 kJ/mol increase over the calculated value is the result of additional intermolecular interactions in the solid state. In solution (5:2 CS2/acetone-d6) it was not possible to stop the tert-butyl group rotation even at the lowest achievable temperature (ca. 150 K). This is consistent with the low-energy mechanism, where the ring inversion is not prevented by crystal packing forces.

Structure and Dynamics of 3,5-Di-tert-butylpyrazole Probed by Combined X-ray Crystallography and 15N Solid State NMR

The crystal structure of the title compound was determined by X-ray crystallography: CIIHZON~, Pbca, 2 = 8, a = 11.4779(3), b = 21.1004(1), c = 9.9801(2) A, D, = 0.99 g ~m-~. The results show that crystals of 3,5-di-tert-butylpyrazole are formed by three types of dimers AA, AB or BA, and BB differing in the conformation of the tert-butyl groups. Variable temperature 15N-CPMAS-NMR experiments which were carried out on a solid I5N-1abeled sample indicate a conformational interconversion of the different dimers via tert-butyl group rotation as well as a nondegenerate intradimer double proton transfer. The rate and equilibrium constants of the tautomerism were obtained by l5N-CPMAS-NMR line-shape analysis. These constants represent averages of the different conformational states. The analysis of the data suggests that the tautomerism takes place only in the symmetric conformer AA where the tautomerism is degenerate. The observed nondegeneracy is then not the consequence of solid state effects, but of the intrinsic conformational exchange.

A carbon-13 CP/MAS NMR study of a double tert-butyl group rotation in the solid state using T1.rho. and line shape measurements

A combination of solid state 13 C CP/MAS NMR techniques has been used to study the rates of rotation of the tert-butyl groups in cis-4-tert-butyl-1-(tert-butylsulfonyl)cyclohexane. The methods employed include line shape analysis and T 1ρ measurements with rates between 6×10 3 and 2×10 7 s -1 over the temperature range 202-320 K. It is demonstrated that 13 C T 1ρ measurements from CP/MAS spectra can give quantitative information on intramolecular motions that agree with that from line shape analysis

Hindered Rotation of tert‐Butyl Groups in Radical Cations of Highly Substituted Alkenes

Hindered Rotation of <i>tert</i>‐Butyl Groups in Radical Cations of Highly Substituted Alkenes

Correlated rotation of tert-butyl groups in tri-tert-butylsilane

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCorrelated rotation of tert-butyl groups in tri-tert-butylsilaneW. Douglas Hounshell, Linda D. Iroff, R. J. Wroczynski, and Kurt MislowCite this: J. Am. Chem. Soc. 1978, 100, 16, 5212–5213Publication Date (Print):August 1, 1978Publication History Published online1 May 2002Published inissue 1 August 1978https://doi.org/10.1021/ja00484a054RIGHTS & PERMISSIONSArticle Views89Altmetric-Citations22LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (321 KB) Get e-Alerts Get e-Alerts