Phase dependence of conformational motions in solids. The tert-butyl rotation in (1R*,2S*,5R*)-5-tert-butyl-2-hydroxycyclopentanecarboxylic acid

Frank G. Riddell, G. Bernáth, F. Fülöp

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Abstract

(1R8*,2S*,5R*)-5-tert-Butyl-2-hydroxycyclopentanecarboxylic acid exists in several solid phases, two of which are investigated in this report: a first phase (phase I) obtained by crystallization from common solvents and a second phase (phase II) obtained by heating the first phase above ca. 70 °C. The second phase appears to be the stable phase at ambient temperature, and the first phase appears to be a metastable phase. A third phase (phase III), which reverts to phase II on standing at room temperature, is obtained by cooling the melt to room temperature. The rates of rotation of the tert-butyl groups in phases I and II have been measured by CP/MAS NMR techniques. The activation parameters for the tert-butyl group rotation differ markedly between the two phases: phase I, ΔH≠ = 59.0 ± 2.1 kJ mol-1, ΔS≠ = 51.6 ± 8.1 J K-1 mol-1; and phase II, ΔH≠ = 43.9 ± 2.5 kJ mol-1, ΔS≠ = 28.3 ± 9.3 J K-1 mol-1. The structure of phase I has been solved by X-ray diffraction techniques, and this assists in understanding the experimental observations.

Original languageEnglish
Pages (from-to)2327-2335
Number of pages9
JournalJournal of the American Chemical Society
Volume117
Issue number8
DOIs
Publication statusPublished - Mar 1 1995

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Temperature
Acids
Metastable phases
Crystallization
X-Ray Diffraction
Heating
Chemical activation
Nuclear magnetic resonance
Cooling
X ray diffraction

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{c11e70c5fb524d0fb1e3e6a515acd05f,
title = "Phase dependence of conformational motions in solids. The tert-butyl rotation in (1R*,2S*,5R*)-5-tert-butyl-2-hydroxycyclopentanecarboxylic acid",
abstract = "(1R8*,2S*,5R*)-5-tert-Butyl-2-hydroxycyclopentanecarboxylic acid exists in several solid phases, two of which are investigated in this report: a first phase (phase I) obtained by crystallization from common solvents and a second phase (phase II) obtained by heating the first phase above ca. 70 °C. The second phase appears to be the stable phase at ambient temperature, and the first phase appears to be a metastable phase. A third phase (phase III), which reverts to phase II on standing at room temperature, is obtained by cooling the melt to room temperature. The rates of rotation of the tert-butyl groups in phases I and II have been measured by CP/MAS NMR techniques. The activation parameters for the tert-butyl group rotation differ markedly between the two phases: phase I, ΔH≠ = 59.0 ± 2.1 kJ mol-1, ΔS≠ = 51.6 ± 8.1 J K-1 mol-1; and phase II, ΔH≠ = 43.9 ± 2.5 kJ mol-1, ΔS≠ = 28.3 ± 9.3 J K-1 mol-1. The structure of phase I has been solved by X-ray diffraction techniques, and this assists in understanding the experimental observations.",
author = "Riddell, {Frank G.} and G. Bern{\'a}th and F. F{\"u}l{\"o}p",
year = "1995",
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T1 - Phase dependence of conformational motions in solids. The tert-butyl rotation in (1R*,2S*,5R*)-5-tert-butyl-2-hydroxycyclopentanecarboxylic acid

AU - Riddell, Frank G.

AU - Bernáth, G.

AU - Fülöp, F.

PY - 1995/3/1

Y1 - 1995/3/1

N2 - (1R8*,2S*,5R*)-5-tert-Butyl-2-hydroxycyclopentanecarboxylic acid exists in several solid phases, two of which are investigated in this report: a first phase (phase I) obtained by crystallization from common solvents and a second phase (phase II) obtained by heating the first phase above ca. 70 °C. The second phase appears to be the stable phase at ambient temperature, and the first phase appears to be a metastable phase. A third phase (phase III), which reverts to phase II on standing at room temperature, is obtained by cooling the melt to room temperature. The rates of rotation of the tert-butyl groups in phases I and II have been measured by CP/MAS NMR techniques. The activation parameters for the tert-butyl group rotation differ markedly between the two phases: phase I, ΔH≠ = 59.0 ± 2.1 kJ mol-1, ΔS≠ = 51.6 ± 8.1 J K-1 mol-1; and phase II, ΔH≠ = 43.9 ± 2.5 kJ mol-1, ΔS≠ = 28.3 ± 9.3 J K-1 mol-1. The structure of phase I has been solved by X-ray diffraction techniques, and this assists in understanding the experimental observations.

AB - (1R8*,2S*,5R*)-5-tert-Butyl-2-hydroxycyclopentanecarboxylic acid exists in several solid phases, two of which are investigated in this report: a first phase (phase I) obtained by crystallization from common solvents and a second phase (phase II) obtained by heating the first phase above ca. 70 °C. The second phase appears to be the stable phase at ambient temperature, and the first phase appears to be a metastable phase. A third phase (phase III), which reverts to phase II on standing at room temperature, is obtained by cooling the melt to room temperature. The rates of rotation of the tert-butyl groups in phases I and II have been measured by CP/MAS NMR techniques. The activation parameters for the tert-butyl group rotation differ markedly between the two phases: phase I, ΔH≠ = 59.0 ± 2.1 kJ mol-1, ΔS≠ = 51.6 ± 8.1 J K-1 mol-1; and phase II, ΔH≠ = 43.9 ± 2.5 kJ mol-1, ΔS≠ = 28.3 ± 9.3 J K-1 mol-1. The structure of phase I has been solved by X-ray diffraction techniques, and this assists in understanding the experimental observations.

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