Comparing Strong and Weak Halogen Bonding in Solution: ¹³C NMR, UV/Vis, Crystallographic, and Computational Studies of an Intramolecular Model

Abstract

A series of arylene ethynylene compounds has been generated in order to study the differences between strong and weak intramolecular halogen bonding in solution. With strong intramolecular halogen bonding, the presence of electron‐withdrawing fluorine substituents near the halogen‐bond donor has a significant impact on the halogen bond and consequently on 13C NMR chemical shifts. UV/Vis studies suggest increased conjugation of the arylene ethynylene backbone when strong halogen bonds are present. UV/Vis and NMR signatures of intramolecular halogen bonding are diminished significantly when electron‐withdrawing fluorine substituents are absent, however. This change in behavior is further illustrated by differences in crystallization tendencies with the presence or absence of electron‐withdrawing substituents. Calculations using the M06‐2X functional provide some insight into the energies associated with both strong and weak intramolecular halogen bonding.

Visible-Light-Driven Halogen-Bond-Assisted Direct Synthesis of Heteroaryl Thioethers Using Transition-Metal-Free One-Pot C–I Bond Formation/C–S Cross-Coupling Reaction

“…1 ppm). This increase in chemical shift indicates a presence of halogen-bonding between iodoisoquinoline and the thiolate anion due to the lengthening of the C–I bond upon donation of the halogen bond acceptor electrons into orbitals of iodine …”

“…This increase in chemical shift indicates a presence of halogen-bonding between iodoisoquinoline and the thiolate anion due to the lengthening of the C−I bond upon donation of the halogen bond acceptor electrons into orbitals of iodine. 26 The density functional theory (DFT) calculations also verified the presence of the halogen bond. The distance between the iodine atom of 4-iodoisoquinoline and the sulfur atom of the benzenethiolate anion in the XB complex was found to be 3.38 Å which is less than the sum of van der Waals radii of S and I (3.78 Å) (Figure 5A).…”

Halogen Bond-Activated Visible-Light-Mediated Regioselective C–H Arylation of 2-Phenylimidazo-[1,2-a]pyridines

“…0.1 ppm). This downfield shift in the peak for the carbon attached to iodine corroborates the halogen bonding interaction between iodobenzene and KO t Bu …”

The Nitrogen Bond, or the Nitrogen-Centered Pnictogen Bond: The Covalently Bound Nitrogen Atom in Molecular Entities and Crystals as a Pnictogen Bond Donor

“…A task group has been charged with categorizing tetrel bonding, pnictogen bonding, and other non-covalent interactions, involving the elements of Groups 14-16 of the periodic table [4]. The proposed characteristics of these bonding interactions have emerged from observations of a variety of engineered chemical systems in the crystalline, liquid and gas phases, and examining signatures arising from IR [5,6], Raman [7,8], UV/vis [9,10], and NMR [10,11] methods, and from ab initio and density functional theory calculations [12][13][14]. The characteristic features vary from system to system because they are dependent on the nature of the electron density distribution associated with the electron donor and electron acceptor fragments driving the non-covalent interactions.…”