Computational Study About Noncovalent Bonding Systems Involving Halogen, Chalcogen and Pnicogen Bonds

First terms used in this thesis are introduced and defined as follows. In the periodic table, the elements in the 17th column are named halogen including fluorine (F), chlorine (Cl), bromine (Br) and iodine (I). The elements in the 16th column are named chalcogen including oxygen (O), sulfur (S), selenium (Se) and tellurium (Te). The elements in the 15th column are named pnicogen including nitrogen (N), phosphorus (P), arsenic (As) and antimony (Sb). After hydrogen bonds (B-H⋅⋅⋅B) are well studied and understood by scientists and researchers, halogen bonds (R-X⋅⋅⋅B) have drawn attention due to the similarities in bonding format and geometries. However, it is not straightforward to understand how the overall negative halogen atoms interact with the electronegative chemical group, which is usually a Lewis base until scientists proved the existence of the positive region surrounding the halogen atom X directly opposite the R group by Molecular Electrostatic Potential analysis. This thesis studied the detailed structural, geometric and spectroscopic features quantitatively by computational chemistry. The research studied the halogen transfer in symmetric (between two same molecules) and asymmetric systems (between two different molecules). In either case, the potential contains a single symmetric well for short halogen bond length and transferred to a double well when the distance was increased. Furthermore, the partial transfer calculations of halogen as bridging atom between two molecules suggests the degree of halogen transfer to form an ion pair is small even when a strong acid is combined with a strong base. Moreover, the thesis extended the application of Badger-Bauer rules from hydrogen bonds to halogen, chalcogen and pnicogen bonds. Badger-Bauer rules states the spectroscopic change were linearly related to the bond strength of hydrogen bonds. The theory extension will improve the understanding of bond strength of a specific bond in the complicated systems by detecting the spectroscopic change