Molecular dynamics of t
 e
 r
 t-butanol studied by neutron transmission

Amáral, L. Q.; Fulfaro, R.; Vinhas, L.A.

doi:10.1063/1.431427

Cited by 11 publications

(5 citation statements)

References 21 publications

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“…It is, therefore, suggested that crystals I and III, likewise liquid, are built on coiled flexible chains of variable length. No appreciable change in the structure at the transition temperatures has been detected in neutron scattering studies [6,7]. The inelastic spectra remain essentially constant in the temperature interval 281-308 K, which is explained in terms of a short range order maintained during transition to liquid and reorientational disorder in solid.…”

Section: Introductionmentioning

confidence: 85%

N.M.R. study of molecular dynamics and phase transitions in solid 2-methyl-2-propanol

Szcześniak

1986

Molecular Physics

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Proton second moment and spin-lattice relaxation times (T 1 and Tip ) have been studied in solid 2-methyl-2-propanol in the temperature interval 77 K to the melting point. The data at low temperatures are satisfactorily explained in terms of simultaneous methyl and t-butyl motions. The activation energies of these motions are of 22-3 and 13"2 kJ mol-1, respectively. At high temperatures the relaxation, particularly Tlo , is influenced by translational diffusion. The energy barrier to this process is estimated roughly to be of about 137kJmol 1. The results confirm the existence of the phase transition at around 287 K and indicate that it may originate from the coupling between internal motions.

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Section: Introductionmentioning

confidence: 85%

N.M.R. study of molecular dynamics and phase transitions in solid 2-methyl-2-propanol

Szcześniak

1986

Molecular Physics

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“…In this phase, the tert -butyl alcohol molecules are bonded together in hexamers, packed in a chairlike conformation . Phase II transforms to phases I or III if kept at 286.14 or 281.54 K, respectively. ,− Phase III can exist between 282 and 295 K and is noncubic. If the sample is pure enough and is given the time to recrystallize between 286 K and the melting point TBA, it transforms to phase IV. , If the cooling rate is fast enough, a glassy state is achieved .…”

Section: Introductionmentioning

confidence: 99%

“…Various experimental techniques such as neutron scattering, , far-IR, low-field 2 H, 1 H, , 13 C, and 17 O NMR were used in an attempt to characterize the molecular reorientations in solid TBA. Unfortunately, the results obtained by different techniques for the solid alcohol are controversial.…”

Section: Introductionmentioning

confidence: 99%

Mobility of Solid tert-Butyl Alcohol Studied by Deuterium NMR

2011

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The molecular mobility of solid deuterated tert-butyl alcohol (TBA) has been studied over a broad temperature range (103–283 K) by means of solid-state 2H NMR spectroscopy, including both line shape and anisotropy of spin–lattice relaxation analyses. It has been found that, while the hydroxyl group of the TBA molecule is immobile on the 2H NMR time scale (τC > 10(–5) s), its butyl group is highly mobile. The mobility is represented by the rotation of the methyl [CD3] groups about their 3-fold axes (C3 rotational axis) and the rotation of the entire butyl [(CD3)3-C] fragment about its 3-fold axis (C3′ rotational axis). Numerical simulations of spectra line shapes reveal that the methyl groups and the butyl fragment exhibit three-site jump rotations about their symmetry axes C3 and C3′ in the temperature range of 103–133 K, with the activation energies and preexponential factors E1 = 21 ± 2 kJ/mol, k(01) = (2.6 ± 0.5) × 10(12) s(–1) and E2 = 16 ± 2 kJ/mol, k(02) = (1 ± 0.2) × 10(12) s(–1), respectively. Analysis of the anisotropy of spin–lattice relaxation has demonstrated that the reorientation mechanism of the butyl fragment changes to a free diffusion rotational mechanism above 173 K, while the rotational mechanism of the methyl groups remains the same. The values of the activation barriers for both rotations at T > 173 K have the values, which are similar to those at 103–133 K. This indicates that the interaction potential defining these motions remains unchanged. The obtained data demonstrate that the detailed analysis of both line shape and anisotropy of spin–lattice relaxation represents a powerful tool to follow the evolution of the molecular reorientation mechanisms in organic solids.

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“…Thus, 2-methyl-2-propanol, on the basis of its low entropy of fusion (ASm = 4.70 eu),3 was first classified as a globular compound having a plastic crystal phase;4 in fact, neutron transmission measurements showed that its small entropy of fusion originates essentially in the ordering of the liquid through hydrogen bonds more than from a high degree of The Journal of Physical Chemistry, Vol. freedom in the solid. 5 The same situation is probably valid for methanol, which was initially thought to have a plastic phase on the basis of its low ASm (4.6 eu). 6 From a structural viewpoint, on the other hand, Timmermans pointed out that plastic behavior was characteristic of globular, i.e., nearly spherically shaped, molecules.1 This globularity has commonly been considered as the structural feature which causes a molecule to exhibit plastic phase behavior.…”

Section: Introductionmentioning

confidence: 86%

“…As far as thermodynamics is concerned, he noted that plastic crystals exhibit a low entropy of fusion, and he proposed as an arbitrary but convenient upper limit of ASm = 5 eu. This value, although it turned out to be satisfactory in most cases, suffers some exceptions; thus, both sulfur hexafluoride and hexachloroethane have been shown to exhibit plastic phases, although their ASm are equal to 5.4 and 5.5 eu, respectively.2 Furthermore, one should remember that ASm is not an absolute measure of the degree of disorder in the solid state, but a measure of the difference in organization between the liquid and the solid.…”

Section: Introductionmentioning

confidence: 99%

Plastic phases in globular phosphorus compounds. A new structural criterion for plastic behavior

Postel¹,

Riess²

1977

J. Phys. Chem.

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Somewhat similar values would be found for = 4 if the low temperature results were given more weight than high temperature ones.Fletcher and Heller7 reported for the cyclization of the 1-octanol tetramer is n-decane AH°c = -3.8 kcal/mol and AS°c = -11.2 cal/deg mol. The agreement between the two sets of data is within the experimental uncertainty. ConclusionsThe results obtained in this study confirm the assignment made in our previous works, namely, that the excess ultrasonic absorption of alcohol solutions in cyclohexane is due to the formation of noncyclic tetramers or pentamers. The values of the activation enthalpy and entropy for the association of one alcohol molecule to an (nl)-mer confirm that this reaction is diffusion controlled. The activation enthalpy and entropy for the dissociation of an alcohol molecule from the stable noncyclic n-mer have been obtained for the first time. These two quantities are positive. The equilibrium thermodynamic quantities for the formation of noncyclic and cyclic species have also been obtained. They are in agreement with those determined by "equilibrium" measurements.Supplementary Material Available: Tables of raw ultrasonic absorption data (3 pages). Ordering information is given on any current masthead page.

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Molecular dynamics of t e r t-butanol studied by neutron transmission

Cited by 11 publications

References 21 publications

N.M.R. study of molecular dynamics and phase transitions in solid 2-methyl-2-propanol

N.M.R. study of molecular dynamics and phase transitions in solid 2-methyl-2-propanol

Mobility of Solid tert-Butyl Alcohol Studied by Deuterium NMR

Plastic phases in globular phosphorus compounds. A new structural criterion for plastic behavior

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