Intramolecular Halogen Bonding in Solution: ¹⁵N, ¹³C, and ¹⁹F NMR Studies of Temperature and Solvent Effects

Abstract

A model system for the investigation of intramolecular halogen bonds is introduced. Two molecules capable of intramolecular halogen bonding have been studied in comparison with eight control compounds by 15N, 13C, and 19F NMR spectroscopy. Iodine‐ and bromine‐centered halogen bonds are indicated by decreases in the 15N NMR chemical shifts of the halogen bond acceptor atom of approximately 6 and 1 ppm, respectively. 13C NMR chemical shifts of the alkynyl carbons in 2‐ethynylpyridine systems are good indicators of halogen bonding, with differences of up to 2.4 ppm between halogen‐bonded and related control compounds. Halogen bond strengths in different solvents, as indicated by 19F NMR chemical shifts, decrease in the following order: Cyclohexane > toluene > benzene > dichloromethane > acetone > pyridine. Chemical shift effects associated with the structural and electronic properties of intramolecular halogen‐bonded systems are modeled well by calculations at the B3LYP/6‐311+G(2d,p) level of theory.

Benchmarking of Halogen Bond Strength in Solution with Nickel Fluorides: Bromine versus Iodine and Perfluoroaryl versus Perfluoroalkyl Donors

“…Bowling and co‐workers used 19 F and 15 N NMR spectroscopy to investigate the formation of intramolecular halogen bonds between a C 6 F 4 X unit (X=I and Br) and a pyridyl moiety (py) in which the halogen bond donor and acceptor units are linked by an aryldiyne spacer. The evidence indicated that the C 6 F 4 Br⋅⋅⋅py interaction is probably significantly weaker than the corresponding C 6 F 4 I⋅⋅⋅py interaction in benzene solution …”

Solvent Effects on Nitrogen Chemical Shifts

“…30, as model systems. Bowling et al studied [153] five sets of isomers, of which two (245 and 247) were designed to be able of forming intramolecular halogen bonds, whereas eight as control systems. The 15 N NMR data, shown in Table 22, of the non-halogen bonding compounds 237-244 were comparable in benzene-d 6 , just as those of 238 and 240.…”

“…The structure of pyridine-functionalized aryldiynes, synthesized to study CdI⋯N and CdBr⋯N halogen bond interactions[153].78 Hanna Andersson et alThus, the chemical shift of 239 differs only by 4.5 ppm from those of 238 and 240, whereas no evidence is seen for the formation of a brominecentered halogen bond for 237 in the more polar solvent. These conclusions were confirmed by additional19 F and 13 C NMR studies.…”

Halogen Bonding in Solution

“…Rissanen et al disclosed the solution NMR study of multivalent halogen bonded deep cavity cavitands [132], whereas Diedrich et al reported the thermodynamics of halogen bonding of substituted (iodoethynyl) benezene derivatives in solution. [133] The solvent and temperature effects on an intramolecular halogen bonding was studied by Bowling et al [134]. The applications of halogen bonding in solution were recently reviewed by Vargas Jetzsch [135].…”