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Open AccessArticle

Understanding the Exceptional Properties of Nitroacetamides in Water: A Computational Model Including the Solvent

by Giovanni La Penna 1,*,† and Fabrizio Machetti 2,*,‡
1
Istituto di Chimica dei Composti Organometallici (ICCOM), Consiglio Nazionale delle Ricerche (CNR), via Madonna Del Piano 10, I-50019 Sesto Fiorentino, Firenze, Italy
2
Istituto di Chimica dei Composti Organometallici (ICCOM), Consiglio Nazionale delle Ricerche (CNR), c/o Dipartimento di Chimica “Ugo Schiff” via Della Lastruccia 13, I-50019 Sesto Fiorentino, Firenze, Italy
*
Authors to whom correspondence should be addressed.
G.L.P. is associated to the Istituto Nazionale di Fisica Nucleare (INFN), Section of Roma-Tor Vergata, via della Ricerca Scientifica 1, I-00133 Roma, Italy.
Dedicated to Prof. Francesco De Sarlo on the occasion of his 80th birthday.
Academic Editor: Michal Szostak
Molecules 2018, 23(12), 3308; https://doi.org/10.3390/molecules23123308
Received: 22 November 2018 / Revised: 7 December 2018 / Accepted: 10 December 2018 / Published: 13 December 2018
(This article belongs to the Special Issue Amide Bond Activation)
Proton transfer in water involving C–H bonds is a challenge and nitro compounds have been studied for many years as good examples. The effect of substituents on acidity of protons geminal to the nitro group is exploited here with new p K a measurements and electronic structure models, the latter including explicit water environment. Substituents with the amide moiety display an exceptional combination of acidity and solubility in water. In order to find a rationale for the unexpected p K a changes in the (ZZ )NCO- substituents, we measured and modeled the p K a with Z=Z =H and Z=Z =methyl. The dominant contribution to the observed p K a can be understood with advanced computational experiments, where the geminal proton is smoothly moved to the solvent bath. These models, mostly based on density-functional theory (DFT), include the explicit solvent (water) and statistical thermal fluctuations. As a first approximation, the change of p K a can be correlated with the average energy difference between the two tautomeric forms (aci and nitro, respectively). The contribution of the solvent molecules interacting with the solute to the proton transfer mechanism is made evident. View Full-Text
Keywords: amides; carbanions; C–H acidity; nitro-aci tautomerism; molecular dynamics; density-functional theory amides; carbanions; C–H acidity; nitro-aci tautomerism; molecular dynamics; density-functional theory
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MDPI and ACS Style

La Penna, G.; Machetti, F. Understanding the Exceptional Properties of Nitroacetamides in Water: A Computational Model Including the Solvent. Molecules 2018, 23, 3308.

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