13C NMR Study of Halogen Bonding of Haloarenes: Measurements of Solvent Effects and Theoretical Analysis
Solvent effects on the NMR spectra of symmetrical (X = F (1), X = Cl (2), X = Br (3), X = I (4), X = NO2 (5), X = CN (6)) and unsymmetrical (X = I, Y = MeO (7), Y = PhO (8)) para-disubstituted acetophenone azines X-C6H4-CMe═N-N═CMe-C6H4-Y and of models X-C6H4-CMe═N-Z (X = I, Z = H (9), Z = NH2 (10)), 4-iodoacetophenone (11), and iodobenzene (12) were measured in CDCI3, DMSO, THF, pyridine, and benzene to address one intramolecular and one intermolecular issue. Solvent effects on the 13C NMR spectra are generally small, and this finding firmly establishes that the azine bridge indeed functions as a "conjugation stopper," an important design concept in our polar materials research. Since intermolecular halogen bonding of haloarenes do occur in polar organic crystalline materials, the NMR solution data pose the question as to whether the absence of solvent shifts indicates the absence of strong halogen bonding in solution. This question was studied by the theoretical analysis of the DMSO complexes of iodoarenes 4, 9-12, and of iodoacetylene. DFT and MP2 computations show iodine bonding, and characteristic structural and electronic features are described. The nonrelativistic complexation shifts and the change in the spin-orbit induced heavy atom effect of iodine compensate each other, and iodine bonding thus has no apparent effect on Ci in the iodoarenes. For iodides, complexation by DMSO occurs and may or may not manifest itself in the NMR spectra. The absence of complexation shifts in the NMR spectra of halides does not exclude the occurrence of halogen bonding in solution.
R. Glaser et al., "13C NMR Study of Halogen Bonding of Haloarenes: Measurements of Solvent Effects and Theoretical Analysis," Journal of the American Chemical Society, vol. 126, no. 13, pp. 4412-4419, American Chemical Society (ACS), Apr 2004.
The definitive version is available at https://doi.org/10.1021/ja0383672
University of Missouri Research Board
University of Missouri Research Council
National Institutes of Health (U.S.)
Keywords and Phrases
Chemical Bonds; Complexation; Nuclear Magnetic Resonance Spectroscopy; Organic Solvents; Halogen Bonding; Solvent Effects; Aromatic Hydrocarbons; 4 Iodoacetophenone; Acetophenone Derivative; Benzene; Chloroform; Dimethyl Sulfoxide; Halide; Halogenated Hydrocarbon; Hydrazine; Iodine Derivative; Iodobenzene; Polycyclic Aromatic Hydrocarbon; Pyridine; Solvent; Unclassified Drug; Carbon Nuclear Magnetic Resonance; Complex Formation; Crystal Structure; Enthalpy; Entropy; Halogen Bond; Proton Nuclear Magnetic Resonance; Theoretical Study; Vibration
International Standard Serial Number (ISSN)
Article - Journal
© 2004 American Chemical Society (ACS), All rights reserved.