Um, Ik-Hwan Kang, Ji-Sun Park, Jong-Yoon Kinetic Study on Michael-Type Reactions of β‑Nitrostyrenes with Cyclic Secondary Amines in Acetonitrile: Transition-State Structures and Reaction Mechanism Deduced from Negative Enthalpy of Activation and Analyses of LFERs A kinetic study is reported for the Michael-type reactions of X-substituted β-nitrostyrenes (<b>1a</b>–<b>j</b>) with a series of cyclic secondary amines in MeCN. The plots of pseudo-first-order rate constant <i>k</i><sub>obsd</sub> vs [amine] curve upward, indicating that the reactions proceed through catalyzed and uncatalyzed routes. The dissection of <i>k</i><sub>obsd</sub> into <i>Kk</i><sub>2</sub> and <i>Kk</i><sub>3</sub> (i.e., the rate constants for the uncatalyzed and catalyzed routes, respectively) revealed that <i>Kk</i><sub>3</sub> is much larger than <i>Kk</i><sub>2</sub>, implying that the reactions proceed mainly through the catalyzed route when [amine] > 0.01 M. Strikingly, the reactivity of β-nitrostyrene (<b>1g</b>) toward piperidine decreases as the reaction temperature increases. Consequently, a negative enthalpy of activation is obtained, indicating that the reaction proceeds through a relatively stable intermediate. The Brønsted-type plots for the reactions of <b>1g</b> are linear with β<sub>nuc</sub> = 0.51 and 0.61, and the Hammett plots for the reactions of <b>1a</b>–<b>j</b> are also linear with ρ<sub>X</sub> = 0.84 and 2.10 for the uncatalyzed and catalyzed routes, respectively. The reactions are concluded to proceed through six-membered cyclic transition states for both the catalyzed and uncatalyzed routes. The effects of the substituent X on reactivity and factors influencing β<sub>nuc</sub> and ρ<sub>X</sub> obtained in this study are discussed. ρ X;uncatalyzed routes;β nuc;Reaction Mechanism Deduced;reaction temperature increases;Kk 3;Br ønsted plots 2016-02-19
    https://acs.figshare.com/articles/journal_contribution/Kinetic_Study_on_Michael_Type_Reactions_of_Nitrostyrenes_with_Cyclic_Secondary_Amines_in_Acetonitrile_Transition_State_Structures_and_Reaction_Mechanism_Deduced_from_Negative_Enthalpy_of_Activation_and_Analyses_of_LFERs/2407939
10.1021/jo4007442.s001