Dimerization constants of atrazine and trifluoromethyl-labeled atrazine

Fluorine-19 Nuclear Magnetic Resonance Study of Atrazine in Humic and Sodium Dodecyl Sulfate Micelles Swollen by Polar and Nonpolar Solvents

“…Conformer I appears as two resonances, Ie and Ii, because sites 1 and 2 form hydrogen bonds independently of one another 21 and, as with IIe and IIIi, the relative magnitude of their influence on the −CF 3 chemical shift differs because of proximity. Conformer I interacting through site 1, resonance Ii, results in weaker perturbations of the label than when conformer I interacts through site 2, resonance Ie; see Figure in ref .…”

“…Each resonance undergoes chemical exchange between a state where the active site is not hydrogen bonded and a state where a hydrogen bond exists at that site. Hydrogen-bonding perturbations result in a larger change in the chemical shift of resonance IIe relative to IIIi because site 3 is closer to the −CF 3 label than site 4; see Figure in ref . Conformer I appears as two resonances, Ie and Ii, because sites 1 and 2 form hydrogen bonds independently of one another 21 and, as with IIe and IIIi, the relative magnitude of their influence on the −CF 3 chemical shift differs because of proximity.…”

“…The relative intensities of each conformer in infinitely dilute solutions reflect their intrinsic stabilities. Dimerization and complexation stabilize certain conformers more than others, leading to changes in the relative populations of each conformer. ,

1 Atrazine adopts four conformations because partial double bonds between the alkylamino side chains and the triazine ring hinder free rotation. The circled Arabic numbers identify the four hydrogen-bond sites and the Roman numerals identify the four conformers.

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“…The two side-chain alkylamino nitrogens serve as hydrogen-bond donors while the ring imino nitrogen serves as a hydrogen-bond acceptor. Intermolecular hydrogen-bond complexes between atrazine and donor or acceptor compounds further alter the relative conformer populations. , Complexing agents with both hydrogen-bond donor and acceptor capacity, e.g., acetic acids and amides, form much stronger complexes with atrazine than complexes employing only one hydrogen-bond site, e.g., ethanol and acetone. − …”

“…The relative abundance of each conformer determines the intensity of each resonance. Conformer IV, which does not dimerize, does not appear because its abundance is negligible …”