title: Molecular interactions between pyrazine and n-propanol, chloroform, or tetrahydrofuran.
abstract: The molecular interactions of pyrazine (PZ) with n-propanol, chloroform, and tetrahydrofuran (THF) have been investigated by employing ultraviolet spectroscopy and quantum chemical calculation methods. A new quantity, excess absorption coefficient, was introduced to represent the strength of the interaction. It was found that the interaction decreased in the order: PZ-propanol>PZ-chloroform>PZ-THF. The Benesi-Hildebrand method indicated that the interaction stoichiometries of the PZ-chloroform and PZ-THF systems were both 1:1 and the equilibrium constants were determined to be 2.07 and 0.64M(-1), respectively. Using a nonlinear fitting method, we demonstrated that the PZ-propanol was a two-step 1:2 interaction pair and the equilibrium constants were determined to be 8.8 and 0.19M(-1). Quantum chemical calculations showed the existence of hydrogen-bonding interactions in all the three system: normal Ncdots, three dots, centeredH-O hydrogen bond in the PZ-propanol system, unconventional Ncdots, three dots, centeredH-C hydrogen bond in the PZ-chloroform, and weak N-C-Hcdots, three dots, centeredO hydrogen bond in the PZ-THF system. Methodologically, we pointed out that special care must be taken when the Benesi-Hildebrand method is used to evaluate 1:2 interactions.
authors.affiliation: Key Laboratory of Bioorganic Phosphorous Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: Qingzhong
authors.initials: Q
authors.lastname: Li
authors.forename: Ruiguang
authors.initials: R
authors.lastname: Wu
authors.forename: Guoshi
authors.initials: G
authors.lastname: Wu
authors.forename: Zhiwu
authors.initials: Z
authors.lastname: Yu
mesh_terms: D000433:1-Propanol / Q000737:chemistry*; D002725:Chloroform / Q000737:chemistry*; D005663:Furans / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011719:Pyrazines / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D005663:Furans; D011719:Pyrazines; C018674:tetrahydrofuran; D002725:Chloroform; D000433:1-Propanol