Conformational statistics of n-butane in the condensed phase and the effects of temperature

Experimental dipolar couplings are obtained from the 1H NMR spectra of n-butane dissolved in a liquid crystal over an 80° temperature range with Covariance Matrix Adaptation Evolutionary Strategies (CMA-ES). These observables are rationalized using a size-and-shape potential [E.E. Burnell, C.A. de Lange, Chem. Rev. 98 (1998) 2359], CI (2k), and with a modified chord model [D.J. Photinos, E.T. Samulski, H. Toriumi, J. Phys. Chem. 94 (1990) 4694], CCd, for the orientational ordering potential. The trans–gauche energy difference, E tg , is temperature dependent when using the CCd model and temperature independent when using the CI (2k) model for the orientational ordering potential.