Bridgehead distortion at the C 1 position of 1-fluoroadamantane revealed by rotational spectroscopy and ab initio calculations

• Published in: Journal of molecular structure Vol. 612; no. 2; pp. 83 - 91
• Main Authors: Legon, A.C., Tizard, J., Kisiel, Z.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 17.07.2002
• Subjects: Centrifugal distortion constants; Microwave spectroscopy; Molecular structure; Rotational spectroscopy; Centrifugal distortion constants; Molecular structure; Rotational spectroscopy; Microwave spectroscopy
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/S0022-2860(02)00078-9

The rotational spectra of the parent isotopomer of the symmetric-top molecule 1-fluoroadamantane and each of its four different singly substituted 13C species have been observed by pulsed-jet Fourier transform microwave spectroscopy. The spectrum of the parent isotopomer was also investigated in the millimetre-wave region to allow high- J transitions to be observed in order to determine accurately the very small centrifugal distortion constants D J and D JK . The rotational constants of these isotopomers were used to establish the r s and the mean r 0 geometries for the carbon atom skeleton. The first of these indicated a bridgehead compression that was confirmed by ab initio calculations. The preferred geometry for the adamantyl cage is that of r 0 quality obtained by fitting the moments of inertia of all five isotopomers investigated in combination with the ab initio geometry appropriately scaled. The three unique values of r(CC) are 1.527, 1.541, and 1.540 Å, with increasing distance from the substituted bridgehead atom, respectively, and r( CF)=1.402 A ̊ .