Heat capacity and thermodynamic properties of [2.2]paracyclophane. Mechanism of the 50.deg.K transition

Andrews, John T. S.; Westrum, Edgar F.

doi:10.1021/j100909a022

Cited by 34 publications

(19 citation statements)

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“…Also the C1-C2-C9-C10 twist angle for the D 2 symmetry has been the subject of controversy in both experimental and theoretical studies. However, a recent study by Wolf et al (Wolf et al, 2014) resolved the conflicting data by providing X-ray structural parameters measured at temperatures ranging from 15 K to 260 K. The authors reported that [2,2]paracyclophane has a twist angle of 12.83 (4)° at 15 K, 10.7 (3)° at 45 K and 0.0° above 55 K. Thus, this result supports the heat-capacity study by Andrews and Westrum (Andrews and Westrum, 1970), in which a hump in the heat capacity curve around 50 K was observed, suggesting the existence of a phase transition at this temperature. Introduction of a substituent to the [2,2]paracyclophane has direct influence on the electronic space structure between the aromatic moieties.…”

Section: Introductionsupporting

confidence: 67%

Theoretical study of substituent effects on the geometry and strain enthalpy in [2,2]paracyclophanes

Michalík

Poliak

Lukeš

2016

Acta Chimica Slovaca

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The substituent effect on the geometry and strain enthalpy of [2,2]paracyclophane is theoretically investigated by density functional theory. Gas-phase calculations were performed for twenty distinct electron donating and electron withdrawing substituents. The largest out-of-plane distortion of phenyl rings is exhibited by —SCN and —CF3 groups. On the other hand, —OH, —CH3 and —F groups show the minimal deformation. The strain enthalpy for unsubstituted [2,2]paracyclophane associated with repulsive forces between phenyl units reached up to 118.5 kJ mol−1. Any substitution causes increase of the strain enthalpy value proportionally to the absolute values of Hammett para-substituent constants. Two separate linear dependences with similar slopes were obtained for monosubstituted as well as double symmetrically substituted derivatives.

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Section: Introductionsupporting

confidence: 67%

Theoretical study of substituent effects on the geometry and strain enthalpy in [2,2]paracyclophanes

Michalík

Poliak

Lukeš

2016

Acta Chimica Slovaca

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“…Our data do not permit us to distinguish explicitly between a static and a dynamic disorder. However, after we had reported the present results (Hope, Bernstein & Trueblood, 1970) a thermodynalrfic study of the hydrocarbon appeared (Andrews & Westrum, 1970), which contains the information needed to settle this question with reasonable confidence. An anomaly in the heat capacity (Cv) near 50 °K led Andrews & Westrum to suggest that at this temperature the majority of the molecules have acquired sufficient energy to permit the twisting motion to become an active vibrational mode, whereas at lower temperatures this is not the case.…”

Section: Discussionmentioning

confidence: 56%

The crystal and molecular structure of 1,1,2,2,9,9,10,10-octafluoro-[2,2]paracyclophane and a reinvestigation of the structure of [2,2]paracyclophane

Hope¹,

Bernstein²,

Trueblood³

1972

Acta Crystallogr Sect B

280

147

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[2.2]Paracyclophane (I), C16H16, crystallizes in the tetragonal system with a= 7.781 (1), c = 9.290 (2)/~, space group P42/mnm, and two molecules per unit cell. 1,1,2,2,9,9,10,10-Octafluoro-[2.2]paracyclophane (II), C16HsFs, crystallizes in the monoclinic system with a=7"994 (2), b=7.986 (2), c= 10"855 (3)/~, fl= 97.84 (1) °, space group P21/n, and two molecules per unit cell. The known structure of (I) was refined with new three-dimensional diffractometer data by full-matrix least-squares methods to R = 0.029 (360 reflections). The structure of (II) was solved by direct methods with three-dimensional diffractometer data and was refined by full-matrix least-squares to R=0.037 (956 reflections). In the initial refinement of each molecule, the substituent atoms on the bridging carbon atoms showed high anisotropy of apparent thermal motion normal to the bridge-substituent bond, this pattern being remarkably similar in the two molecules. Final refinement was done with a model in which each molecule is statistically disordered, to simulate a dynamic disorder that occurs by a twist of the aromatic rings in opposite directions about their common normal; this model is in accord with spectroscopic and thermodynamic measurements on the hydrocarbon. The amplitude of this motion is found to be about 3 ° for each molecule. The carbon skeletons of (I) and (II) are very similar. The bridge C-C distance is about 1.59 ,~. The average C-F distance is 1"35 /~ and the average F-C-F angle is 106 °. The planes of the four unsubstituted C atoms of each ring are 3.09 A apart. The para carbon atoms are bent about 12 ° out of the plane of the other four atoms of the aromatic ring.

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“…twist. (3)(4)(5) Although a value for the enthalpy of combustion, AH~, for [2.2]-paracyclophane has been reported (6) and the strain in the system apportioned between component contributions, the availability of a well-characterized sample for which thermal measurements have been reported, (4) permitted independent redetermination of the thermochemical properties and strain for this system. Determination of the Present address: Liquid Crystal Institute, Kent State University, Kent, Ohio.…”

Section: Introductionmentioning

confidence: 99%

The enthalpies of combustion and formation of [2.2]-paracyclophane and triptycene

Rodgers¹,

Westrum²,

Andrews³

1973

The Journal of Chemical Thermodynamics

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Heat capacity and thermodynamic properties of [2.2]paracyclophane. Mechanism of the 50.deg.K transition

Cited by 34 publications

References 0 publications

Theoretical study of substituent effects on the geometry and strain enthalpy in [2,2]paracyclophanes

Theoretical study of substituent effects on the geometry and strain enthalpy in [2,2]paracyclophanes

The crystal and molecular structure of 1,1,2,2,9,9,10,10-octafluoro-[2,2]paracyclophane and a reinvestigation of the structure of [2,2]paracyclophane

The enthalpies of combustion and formation of [2.2]-paracyclophane and triptycene

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