Journal of the Chemical Society, Faraday Transactions
Journal of the Chemical Society, Faraday Transactions; was published from 1990 - 1998. In 1999 it merged with a number of European chemical society physical Chemistry journals to become Physical Chemistry Chemical Physics.
Paper
J. Chem. Soc., Faraday Trans., 1998, 94, 2675 - 2680, DOI: 10.1039/a804541k
Evidence concerning the relative nucleophilicities of non-bonding and
-bonding electrons in furan from the rotational spectrum of furan···ClFStephen A. Cooke, Gary K. Corlett, John H. Holloway and A. C. Legon
The rotational spectra of the three isotopomers C4H4O···35ClF, C4H4O···37ClF and C4D4O···35ClF of a complex formed between furan and chlorine monofluoride have been observed by means of a pulsed-nozzle, Fourier-transform microwave spectrometer fitted with a fast-mixing nozzle to preclude any chemical reaction among the component gases. Transitions allowed by all three components µa, µb and µc of the electric dipole moment were observed, those associated with µc exhibiting a small doubling (ca. 20 kHz). Spectral analysis yielded rotational constants, centrifugal distortion constants and (for the isotopomers C4H4O···35ClF and C4H4O···37ClF) all five independent components of the Cl nuclear quadrupole coupling tensor
(, =a, b, c). Diagonalisation of the tensor led to the values of the components ii (i=x, y, z) in the ClF principal axis system and the direction cosines 
z (=a, b, c) relating the ClF axis (z) to the principal inertial axis system. The geometry obtained by fitting the principal moments of inertia of the three observed isotopomers is consistent with the z values and has the ClF subunit approximately perpendicular to one of the C(2)–C(3) bonds of furan. The end 
+Cl of ClF thus appears to interact with the 
electron density between these two atoms. The distance of the Cl atom from the point of intersection of the extrapolated ClF axis with the ring is r(···Cl)=2.726 Ĺ. The doubling of the c-type transitions is interpreted in terms of a motion in which the interaction switches from C(2)–C(3) to C(2
)–C(3). The contrast between the angular geometries of furan···HCl and furan···ClF is discussed in the context of the relative nucleophilicities of the n-pair and the aromatic -electrons of furan.
