Abstract
The molecular structure of cycloheptane (C7H14) has been investigated in the gas phase by electron diffraction. Diffraction intensities can be explained by a twist–chair/chair mixture with an abundance of 76(6) % for the twist–chair conformation at 310°K. Using the nomenclature of J. Cremer and J. A. Pople [J. Am. Chem. Soc. 97, 1354 (1975)] the puckering coordinates were found to be q2=0.529 Å, q3=0.645 Å for the twist–chair and q2=0.487 Å, q3=0.715 Å for the chair form. Other geometrical parameters are: C–C=1.538 Å, C–H=1.112 Å, &C–C–C aver.=115.3° (twist–chair) and 113.5° (chair). Experimental geometries and vibrational amplitudes agree well with those obtained from force field calculations.

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