本文利用動力核磁共振研究不同取代基之苯二酚化合物之立體動態學，了解影響受阻旋轉能障的原因，討論不同取代基，結構，溶劑對受阻旋轉的影響。首先將待測物經由 VT-NMR 測量後，得到不同溫度之光譜資訊，再利用 lineshape analysis 求出不同溫度下之速率常數，配合 Arrehenius equation 和 Eyring equation 即可求出energy of activation，ΔG*，ΔH*，ΔS*，最後再利用二維同核光譜加以驗證。
結果顯示分子在升溫過程中 (270K~310K)，獲得能量足以克服旋轉能障後就逐漸解凍，由 restricted rotation 變成 free rotation，低溫兩組訊號，高溫變為一組訊號的現象可由 NOSEY 光譜驗證。取代基 –OH 易與溶劑水或因溫度上升打斷分子內氫鍵，使其化學位移對溫度變化幅度大。a、b與兩側取代基距離近且體積都很大，steric effect 大，所以ΔH* 大，rotation barrier 較高，Ea大，為 enthalpy effect。在極性高 solvent 中，ΔS*大，受 solvent effect 影響顯著而使 得ΔG* 大，為 entropy effect 。化合物 C 因為結構裡的取代基丁基的凡得瓦爾半徑大，造成立體障礙大，所以旋轉能障高，使 Tc 高，ΔG* 大。

Variable-Teperature Nuclear Magnetic Resonance (VT-NMR) spectroscopy tecnique has been performed on 1,4-hydroquinone-derived atropisomers to investigate the stereodynamics of different restricted rotations in 4-acetoxy-2-benzoyl-3-(1-methyl-2-oxopropyl)naphthalenol (A),4-acetoxy-2-benzoyl-5,6-dimethyl-3-(1-methyl-2-oxopropyl)phenol(B),and 4-acetoxy-2-benzoyl-5,6-dimethyl-3-(1-butyl-2-oxopropyl)phenol (C) in several solvents such as chloroform, toluene, dimethylforamide, tetrahydrofuran, and methanol within the accessible temperature range of 193-363 K. By means of VT-NMR experiments, the corresponding spectra at different temperature were obtained. The rate constants of the restricted rotations were obtained via line shape analysis and followed by evaluation of kinetic parameters, ex: activation energy (Ea), the Gibbs energy of activation (ΔG*), enthalpy of activation (ΔH*), and entropy of activation (ΔS*), using Arrehenius equation and Eyring equation. The proposed restricted-rotation mechanism resulting in the splitting of spectra at lower temperatures could be also confirmed by the 2D-NOE spectra.
Analysis of experimental results manifest that the molecules changed restricted rotation to free rotation because of that the molecules obtained enough energy to overcome the rotational barriers and unfrozen step by step in the process of temperature increasing. In protic solvent such as methanol, the rupture of the intramolecular hydrogen bond between the –OH and the carbonyl group was observed with increasing temperature and meanwhile the temperature factor (H/T) for the corresponding H in the –OH showed a relatively large value (0.5 ~ 6.2 Hz/K) due to the intramolecular H-bond breaking.
On the basis of the obtained activation parameters, in less polar solvents (toluene, chloroform) steric hindrance (large ΔH*) of rotating substituent moiety dominates the rotation barrier (enthalpic effect), whereas in the case of polar solvent methanol, solvent entropic effect (large ΔS*) becomes the prevalling energetic contribution to the barrier to the restricted rotation of those nonpolar substituentts. The high merging temperature (Tc, 310 K) and large ΔG* value (62.8 kJ/mol) for the n-butyl in compound C is ascribed to the large steric hindrance because of relatively large van der Waals radius of butyl group.

1. Gutowsky H. S.; Saika, A. J. Chem. Phys. 1953, 21, 1688.
2. Gutowsky,H. S.;Holm, C.H. J. Chem. Phys. 1956, 25, 1228.
3. Newmark, R. A.; Sederholm, C. H. J. Chem. Phys. 1965, 43, 602.
4. Cotton, F. A. Accounts Chem. Res. 1968, 1, 257.
5. Vrieze, k.; van Leeuwen, P. W. N. M. Progr. Inorg. Chem. 1971,
14, 1.
6. Booth, H.; Khedarir K. A.; Readshaw, S. A. Tetrahedron. 1987, 43, 4399
7. Casarini, D.; Lunazzi.; Maccianitelle, D. J. Chem. Soc.,
Perkin Trans. 2. 1922, 1363
8. Huang, Y.; Macura, S.; Ernst, R. R. J. Amer. Chem. Soc. 1981, 103, 5327.
9. Molday, R. S.; Kallen, R. G. J. Amer. Chem. Soc. 1970, 92, 4527.
10. Casarini, D.; Lunazzi, L.;Anderson, J. E. J. Org. Chem., 1993, 58, 714.
11. Anderson, J. E.; Kirsch, P. A. J. Chem. Soc. Perkin Trans. 2. 1922, 1951.
12. Barreto, R. D; Puga, J; Fehlner, T. P. Organometallics. 1990, 9, 662
13. Gerhard Bringmann, Anne J. Price Mortimer, Paul A. Keller, Mary J. Gresser, James Garner, Matthias Breuning. Angewandte Chemie International Edition. 2005, 44, 5384.
14. Oki, M; Topics in Stereochemistry 1983, 1.
15. Francis P, G. ; Nancy H. K. J. Chem. Edu. 1977, 258.
16. Lodovico, Lunazzi Michele Mancinelli, and Andrea Mazzanti,
J. Org. Chem. 2008. 73, 2198.
17. Aparna Anand, Abhijeet Deb Roy, Ruchika Chakrabarty, Anil K. Saxena, Raja Roy, Tetrahedron, 2007. 63, 5236
18. Ali Reaz Modarresi-Alam, Parisa Najafi, Mohsen Rostamizadeh, Hossein Keukha, Hamid-reza Bijanzadeh, and Erich Kleinpeter,
J. Org. Chem. 2007, 72, 2208.
19. Carlos Jaramillo, Jose Eugenio de Diego, Alfonso Rivera-Sagredo, Chafiq Hamdouchi and Juan F. Espinosa, Tetrahedron. 2006, 62, 12415.
20. Ignacio Alfonso, M. Isabel Burguete, and Santiago V. Luis*,
J. Org. Chem. 2006, 71, 2242.
21. 陳亞文,國立成功大學化學研究所碩士論文,1994.