Validation of Enthalpy-Entropy Compensation Mechanism in Partial Amide Bond Rotation

Jacob Guerra, Bhvandip Bajwa, Prarthana Kumar, Salvador Vazquez, Viswanathan V. Krishnan, Santanu Maitra

Research output: Contribution to journalArticle

Abstract

The concept of enthalpy-entropy compensation (EEC) is one of the highly debated areas of thermodynamics. The conformational change due to restricted double-bond rotation shows a classic two-site chemical exchange phenomenon and has been extensively studied. Fifty-four analogs of N,N-diethyl-m-toluamide (DEET) as a model system were synthesized to study the thermodynamics of the partial amide bond character using nuclear magnetic resonance (NMR) spectroscopy. Line-shape analysis as a function of temperature is used to estimate the chemical exchange. Eyring analysis was then used to convert the chemical exchange rates to determine the transition state enthalpy and entropy of the molecules. The experimental design follows selective variations that perturb one aspect of the molecular system and its influence on the observed thermodynamic effect. The results of the study demonstrate that amide bond resonance in analogs of DEET follows an EEC mechanism. Simple modifications made to DEET's structural motif alter both the enthalpy and entropy of the system and were limited overall to a temperature compensation factor, Tβ = 292.20 K, 95% CI [290.66, 293.73]. We suggest EEC as a model to describe the kinetic compensation seen in chemical exchange phenomena in analogs of DEET.

Original languageEnglish (US)
JournalACS Omega
DOIs
StateAccepted/In press - Jan 1 2020

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)

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