Kinetics, isotope effects of the reaction of 1-(4-nitrophenyl)-1-nitroalkanes with DBU in tetrahydrofuran and chlorobenzene solvents
In: Canadian Journal of Chemistry, Jg. 68 (1990-12-01), S. 2242-2248
Online
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Zugriff:
The kinetics of the reaction of[Formula: see text](R = Me, Et, i-Pr; NPNE, NPNP, MNPNP respectively; L is H or D) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) base in tetrahydrofuran (THF) and chlorobenzene (CB) solvents are reported. The products of these proton transfer reactions are ion pairs absorbing at λmax = 460–480 nm. The equilibrium constants in THF were [Formula: see text]and in CB [Formula: see text]for NPNE, NPNP, MNPNP respectively. The thermodynamic parameters of the reactions are also quoted. The substrate reacts with DBU in both THF and CB solvents in a normal second-order proton transfer reaction. In the case of deuteron transfer, isotopic D/H exchange is much faster than internal return. The reactions show low values of enthalpy of activation ΔH* = 14.3, 18.1, 24.2 and 13.0, 15.1, 18.6 kJmol−1 for NPNE, NPNP, and MNPNP in THF and CB respectively, and large negative entropies of activation −ΔS* = 141, 139, 146; 140, 146, 160 J mol−1 deg−1 for the same sequence of substrates and solvents. The kinetic isotope effects are large, (kH/kD)20°c = 12.2, 13.0, 10.1; 12.9, 12.0, 10.2 for the above sequence of substrates and solvents, and show no difference with changes in either steric hindrance of the C-acids or polarity of the solvents. Keywords: proton transfer, kinetic isotope effect.
Titel: |
Kinetics, isotope effects of the reaction of 1-(4-nitrophenyl)-1-nitroalkanes with DBU in tetrahydrofuran and chlorobenzene solvents
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Autor/in / Beteiligte Person: | Galezowski, Wlodzimierz ; Jarczewski, Arnold |
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Zeitschrift: | Canadian Journal of Chemistry, Jg. 68 (1990-12-01), S. 2242-2248 |
Veröffentlichung: | Canadian Science Publishing, 1990 |
Medientyp: | unknown |
ISSN: | 1480-3291 (print) ; 0008-4042 (print) |
DOI: | 10.1139/v90-345 |
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