DIMERIZATION CONSTANTS OF ATRAZINE AND CF3-LABELED ATRAZINE

A nonlinear optimization procedure is developed to find the dimerizati on constants of atrazine from the NMR chemical shifts of four of its N H protons. The NH protons identify four active sites which interact pa irwise by cooperative association to form a total of 10 hydrogen-bonde d dimers. Each active site is assumed to have a partial dimerization c onstant related to its chemical potential, and the partial constants a re used to develop equations which fit the chemical shift data to a co operative dimerization model. Partial dimerization constants are multi plied together pairwise to obtain the dimerization constant for each o f the 10 atrazine dimers. The partial dimerization constants are also used to measure the effect of a CF3 label on hydrogen bonding and to s how that dimerization constants can be obtained from either F-19 NMR o r H-1 NMR data. The CF3 label enhances the hydrogen-bond donating abil ity of adjacent NH protons by about 20%, resulting in a higher dimeriz ation constant for CF3-labeled atrazine (86 +/- 10 M-1) compared to th at for atrazine (62 +/- 6 M-1).