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Volumn 64, Issue 6, 1999, Pages 2085-2095

Conformational studies in the cyclohexane series. 1. Experimental and computational investigation of methyl, ethyl, isopropyl, and tert- butylcyclohexanes

Author keywords

[No Author keywords available]

Indexed keywords

CYCLOHEXANE DERIVATIVE; METHYL GROUP;

EID: 0033583014     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo990056f     Document Type: Article
Times cited : (130)

References (48)
  • 9
    • 0000751551 scopus 로고
    • Juaristi, E., Ed.; VCH Publishers: New York
    • (a) Previous ab initio studies of monosubstituted cyclohexanes have been reviewed and the difficulties attending such calculations have been discussed; see: Cremer, D.; Szabo, K. J. In Conformational Behavior of Six-Membered Rings; Juaristi, E., Ed.; VCH Publishers: New York, 1995; pp 59-135.
    • (1995) Conformational Behavior of Six-membered Rings , pp. 59-135
    • Cremer, D.1    Szabo, K.J.2
  • 14
    • 0000937514 scopus 로고
    • 13C NMR of a neat sample in an elegantly simple experiment described by Anet and co-workers. This work, which represents the first direct determination of K for the axial-equatorial equilibrium of 1, provided a conformational free energy (-ΔG°) of 1.6 kcal/mol. See: Anet, F. A. L.; Bradley, C. H.; Buchanan, G. W. J. Am. Chem. Soc. 1971, 93, 258.
    • (1971) J. Am. Chem. Soc. , vol.93 , pp. 258
    • Anet, F.A.L.1    Bradley, C.H.2    Buchanan, G.W.3
  • 15
    • 37049103958 scopus 로고
    • (b) A minimum value of 1.8 kcal/mol for the conformational free energy of a methyl group was reported by Subbotin and Sergeyev from a low-temperature NMR study of 1; see: Subbotin, O. A.; Sergeyev, N. M. J. Chem. Soc., Chem. Commun. 1976, 141.
    • (1976) J. Chem. Soc., Chem. Commun. , pp. 141
    • Subbotin, O.A.1    Sergeyev, N.M.2
  • 16
    • 0000005609 scopus 로고
    • Eliel and Wilen (ref 4, p 702) note that the energy difference between cis-and trans-1,3-dimethylcyclohexane should be close to that of the conformational energy of a methyl group. The experimental energy difference for the former pair is 1.7 ± 0.6 kcal/mol in the liquid phase and 1.9 ± 0.6 kcal/mol in the gas phase (Osborne, N. S.; Giddings, D. C. J. Res. Natl. Bur. Stand. 1947, 39, 453). It is well recognized that the energy difference between conformational isomers is often phase dependent (cf. ref 4, pp 600 and 710). The origin of the solvent effect on conformational energy differences has been interpreted in terms of the von Auwers-Skita rule which states that the isomer of higher enthalpy content has the smaller molecular volume, see: Allinger, N. L. J. Am. Chem. Soc. 1957, 79, 3443. Since the isomer of smaller molecular volume will have the higher heat of vaporization, there is no a priori reason to expect conformational energies determined in solution to be identical in magnitude to those observed in the vapor phase.
    • (1947) J. Res. Natl. Bur. Stand. , vol.39 , pp. 453
    • Osborne, N.S.1    Giddings, D.C.2
  • 17
    • 0344024788 scopus 로고
    • Eliel and Wilen (ref 4, p 702) note that the energy difference between cis-and trans-1,3-dimethylcyclohexane should be close to that of the conformational energy of a methyl group. The experimental energy difference for the former pair is 1.7 ± 0.6 kcal/mol in the liquid phase and 1.9 ± 0.6 kcal/mol in the gas phase (Osborne, N. S.; Giddings, D. C. J. Res. Natl. Bur. Stand. 1947, 39, 453). It is well recognized that the energy difference between conformational isomers is often phase dependent (cf. ref 4, pp 600 and 710). The origin of the solvent effect on conformational energy differences has been interpreted in terms of the von Auwers-Skita rule which states that the isomer of higher enthalpy content has the smaller molecular volume, see: Allinger, N. L. J. Am. Chem. Soc. 1957, 79, 3443. Since the isomer of smaller molecular volume will have the higher heat of vaporization, there is no a priori reason to expect conformational energies determined in solution to be identical in magnitude to those observed in the vapor phase.
    • (1957) J. Am. Chem. Soc. , vol.79 , pp. 3443
    • Allinger, N.L.1
  • 18
    • 0345318909 scopus 로고    scopus 로고
    • note
    • Equilibrium constants (equatorial/axial) reported in ref 11, p 259, for methylcyclohexane (1) and isopropylcyclohexane (3) are as follows [K (temperature, absolute)]: 1 K = 426.7 (149), 222.5 (160), 183.0 (167), 164.2 (172); 3 K = 723 (149), 617 (155), 629 (162), 561 (169), 323 (175).
  • 20
    • 0344887735 scopus 로고    scopus 로고
    • note
    • The conformational enthalpy and entropy of the ethyl group in ethylcyclohexane (2) reported in ref 11 (ΔH° = -1.60 ± 0.06 kcal/mol, ΔS° = 0.64 ± 0.35 eu) were determined by the counterpoise technique using cis-1-ethyl-4-methylcyclohexane.
  • 23
    • 0344024786 scopus 로고    scopus 로고
    • note
    • NMR bands should have a Lorentzian line shape. The area of a Lorentzian is given by (height × π)/Γ, where Γ is 2/width at half-height.
  • 29
    • 0345318906 scopus 로고
    • Ph.D. Dissertation, Yale University, New Haven, CT
    • Kates, M. R. Ph.D. Dissertation, Yale University, New Haven, CT, 1978.
    • (1978)
    • Kates, M.R.1
  • 30
    • 0000169232 scopus 로고
    • The uncertainties in the slope and intercept were estimated using the Marquardt algorithm and correspond to one standard deviation: Marquardt, D. W. J. Soc. Indust. Appl. Math. 1963, 11, 431.
    • (1963) J. Soc. Indust. Appl. Math. , vol.11 , pp. 431
    • Marquardt, D.W.1
  • 31
    • 0344024785 scopus 로고    scopus 로고
    • note
    • Additional theoretical levels and details of the thermal corrections to 298 K are given in the Supporting Information.
  • 38
    • 0344024783 scopus 로고    scopus 로고
    • note
    • The B3LYP/6-311G* energies for n-pentane and neopentane are -197.813 79 and -197.815 34 H, respectively, giving a calculated energy difference of only 0.97 kcal/mol, or after correction for the difference in zero-point energy, 1.6 kcal/mol at 0 K. The experimental energy difference (ref 31) is 3.4 kcal/mol at 0 K.
  • 42
    • 0344024776 scopus 로고    scopus 로고
    • note
    • (c) For a concise discussion of the conformational analysis of 2,3-dimethylbutane and related molecules, see ref 4, p 605-606 and references therein.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.