6.3 Molecular Deformation
139
molecular crystals [64–68]. We will discuss other examples and the physical meaning
of the issue in Sect. 10.1.
Conformationally disordered states are usually impossible to discern from the orientationally disordered state in terms of crystallography using scattering techniques.
Indeed, the energetic situation is also expected to resemble that in a supposed disordered state. Thus, it is hard to imagine a phase sequence in which an orientational
melting occurs at a higher temperature than an intramolecular conformational disordering transition, though such a sequence is theoretically possible. On the other hand,
an orientational melting obscures the interaction between different conformations of
neighboring molecules. Thus, the disordering of internal conformation indeed happens but proceeds without a phase transition. CFCl 2 –CFCl 2 shows a symptom of
such a situation as a glass transition (the subject of Chap. 8) concerning the thermal
change of conformational equilibrium [69]. In this compound, the difficulty in obtaining conformational order is suggested as a possible origin of difficulty in reaching
an orientationally ordered crystal obeying the third-law of thermodynamics.
Ironically, a liquid may exhibit a phase transition related to the change in molecular
conformations. Some achiral liquid crystalline compounds exhibit optically active
isotropic liquids [70–73]. They are achiral in a sense as a dynamical average of two
chiral conformations, which are easily interchangeable into each other as a result
of thermal motion. Since their molecules can adopt one of the chiral conformations
in response to their chiral environment (adaptive chirality), they can form chiral
phase(s) in a limited situation. At high temperatures, needless to say, they become
an achiral liquid.
References
1. K. Clusius, Z. Phys. Chem. B31, 459–474 (1936)
2. P. Flubacher, A.J. Leadbetter, J.A. Morrison, Proc. Roy. Soc. 78, 1449–1461 (1961)
3. R.H. Beaumont, H. Chihara, J.A. Morrison, Proc. Roy. Soc. 78, 1462–1481 (1961)
4. K. Clusius, L. Roccoboni, Z. Phys. Chem. B38, 81–95 (1937)
5. W.F. Giauque, J.O. Clayton, J. Am. Chem. Soc. 55, 4875–4889 (1933)
6. C.H. Fagerstroem, A.C.H. Hallett, Ann. Acad. Sci. FennicæA VI 210, 210–213 (1961)
7. J.-H. Hu, D. White, H.L. Johnston, J. Am. Chem. Soc. 75, 5642–5645 (1953)
8. E.K. Gill, J.A. Morrison, J. Chem. Phys. 45, 1585–5645 (1953)
9. T. Atake, H. Chihara, Chem. Lett., 4129–688 (1976)
10. W.F. Giauque, T.M. Powell, J. Am. Chem. Soc. 61, 1970–1974 (1939)
11. D.L. Hildenbrand, W.R. Kramer, R.A. McDonald, D.R. Stull, J. Am. Chem. Soc. 80, 4129–4132
(1958)
12. J.A. Morrison, E.J. Richards, J. Chem. Thermodyn. 8, 1033–1038 (1976)
13. G.G. Devyatykh, A.V. Guesev, A.M. Gibin, N.V. Zhernenkov, L.M. Zakharov, M. Yu, Antipin,
Y.M.T. Struchov, Russ. J. Inorg. Chem. 30, 780 (1985)
14. G.G. Devyatykh, A.V. Gusev, A.M. Gibin, N.V. Zhernenkov, A.V. Kabanov, Zh. Neorg. Khim.
31, 2223–2226 (1986)
15. I.E. Paukov, Y.G Stenin, G.I. Frolova, Zh. Fiz. Khim. 53, 2636–2637 (1979)
16. G.D. Oliver, M. Eaton, H.M. Huffman, J. Am. Chem. Soc. 70, 1502–1505 (1948)
17. R.D. Chirico, S.E. Knipmeyer, W.V. Steele, J. Chem. Thermodyn. 34, 1873–1884 (2002)
139
molecular crystals [64–68]. We will discuss other examples and the physical meaning
of the issue in Sect. 10.1.
Conformationally disordered states are usually impossible to discern from the orientationally disordered state in terms of crystallography using scattering techniques.
Indeed, the energetic situation is also expected to resemble that in a supposed disordered state. Thus, it is hard to imagine a phase sequence in which an orientational
melting occurs at a higher temperature than an intramolecular conformational disordering transition, though such a sequence is theoretically possible. On the other hand,
an orientational melting obscures the interaction between different conformations of
neighboring molecules. Thus, the disordering of internal conformation indeed happens but proceeds without a phase transition. CFCl 2 –CFCl 2 shows a symptom of
such a situation as a glass transition (the subject of Chap. 8) concerning the thermal
change of conformational equilibrium [69]. In this compound, the difficulty in obtaining conformational order is suggested as a possible origin of difficulty in reaching
an orientationally ordered crystal obeying the third-law of thermodynamics.
Ironically, a liquid may exhibit a phase transition related to the change in molecular
conformations. Some achiral liquid crystalline compounds exhibit optically active
isotropic liquids [70–73]. They are achiral in a sense as a dynamical average of two
chiral conformations, which are easily interchangeable into each other as a result
of thermal motion. Since their molecules can adopt one of the chiral conformations
in response to their chiral environment (adaptive chirality), they can form chiral
phase(s) in a limited situation. At high temperatures, needless to say, they become
an achiral liquid.
References
1. K. Clusius, Z. Phys. Chem. B31, 459–474 (1936)
2. P. Flubacher, A.J. Leadbetter, J.A. Morrison, Proc. Roy. Soc. 78, 1449–1461 (1961)
3. R.H. Beaumont, H. Chihara, J.A. Morrison, Proc. Roy. Soc. 78, 1462–1481 (1961)
4. K. Clusius, L. Roccoboni, Z. Phys. Chem. B38, 81–95 (1937)
5. W.F. Giauque, J.O. Clayton, J. Am. Chem. Soc. 55, 4875–4889 (1933)
6. C.H. Fagerstroem, A.C.H. Hallett, Ann. Acad. Sci. FennicæA VI 210, 210–213 (1961)
7. J.-H. Hu, D. White, H.L. Johnston, J. Am. Chem. Soc. 75, 5642–5645 (1953)
8. E.K. Gill, J.A. Morrison, J. Chem. Phys. 45, 1585–5645 (1953)
9. T. Atake, H. Chihara, Chem. Lett., 4129–688 (1976)
10. W.F. Giauque, T.M. Powell, J. Am. Chem. Soc. 61, 1970–1974 (1939)
11. D.L. Hildenbrand, W.R. Kramer, R.A. McDonald, D.R. Stull, J. Am. Chem. Soc. 80, 4129–4132
(1958)
12. J.A. Morrison, E.J. Richards, J. Chem. Thermodyn. 8, 1033–1038 (1976)
13. G.G. Devyatykh, A.V. Guesev, A.M. Gibin, N.V. Zhernenkov, L.M. Zakharov, M. Yu, Antipin,
Y.M.T. Struchov, Russ. J. Inorg. Chem. 30, 780 (1985)
14. G.G. Devyatykh, A.V. Gusev, A.M. Gibin, N.V. Zhernenkov, A.V. Kabanov, Zh. Neorg. Khim.
31, 2223–2226 (1986)
15. I.E. Paukov, Y.G Stenin, G.I. Frolova, Zh. Fiz. Khim. 53, 2636–2637 (1979)
16. G.D. Oliver, M. Eaton, H.M. Huffman, J. Am. Chem. Soc. 70, 1502–1505 (1948)
17. R.D. Chirico, S.E. Knipmeyer, W.V. Steele, J. Chem. Thermodyn. 34, 1873–1884 (2002)