Toluene Torsional angles

Structural Considerations.—The crystal structure of the asymmetrically substituted cis, trans-2,5-di-t-butylcyclohexyl toluene-p-sulphonate (l)has been determined. The mean torsion angle of the cyclohexane ring in (1) is 55.1°, slightly less than the value of 55.9° for cyclohexane. Newman projections along the C-2—C-7 and C-5—C-11 bonds... 

A general attribute of /i-fold barriers where n is large is that Erot tends to be small. For example, Eroi for nitromethane is 0.006 Real /mol, and for toluene it is < 0.1 kcal/mol. One way to rationalize the low barriers is to appreciate that for toluene to have a 3 Real/mol barrier like ethane but still be six-fold, the energy of the system would have to change very rapidly in response to only small changes in torsional angle. This rapid fluctuation in energy is an unreasonable situation. 

Even so for the symmetric structures, CUPWAL, DACLUO and DUTBUP, variations in torsion angles of ca 10° are found. The 0...0 distances around the cone average at 2.67A for molecules with = H. Only one structure for calix[5]arene is available in the database [58], BIMXIE, calix[5]arene bis(acetone)clathrate though recently two other structures (called XXXXXX,YYYYYY in Table 1) have been determined viz tetramethylbutylcalix[5]arene and tetramethylbutylcalix[5]arene toluene clathrate [68]. As is apparent from the torsion angles in Table 1, these three structures have relatively similar conformations. The 0...0 distances around the cone average at 2.84A. 

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