Conformational and isomerizational studies of 3-N,N-dimethylhydrazino-2-methylsulfonyl propenenitrile using NMR and vibrational spectra, X-ray analysis and ab initio calculations

Gróf, Martin; Gatial, A.; Milata, Viktor; Prónayová, Naďa; Kožı́šek, Jozef; Breza, Martin; Matějka, Pavel

doi:10.1016/j.molstruc.2008.03.023

Cited by 3 publications

(2 citation statements)

References 29 publications

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“…One such class of probe molecules is the push–pull ethylenes, − but the concept of a push–pull system also goes well beyond ethylenes. − These are molecules containing multiple bonds with electron-withdrawing groups on one end and electron-donating groups on the other. Under normal circumstances, rotation around multiple bonds is rarely seen because it involves breaking a formal chemical bond.…”

Section: Introductionmentioning

confidence: 99%

“…Electronic structure calculations play a key role in the study of these systems. ,,− ,, The molecules are small enough that high-quality calculations can be done and the details of the electronic structure, such as the full chemical shielding tensors, can be probed. Furthermore, techniques are now available to calculate solvent effects − in a reliable fashion.…”

Section: Introductionmentioning

confidence: 99%

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Solvent Effects on Chemical Exchange in a Push–Pull Ethylene as Studied by NMR and Electronic Structure Calculations

et al. 2011

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NMR measurements of chemical exchange in a push-pull ethylene, dissolved in a number of different solvents, are presented. These are complemented by high-level electronic structure calculations, using both gas-phase conditions and those which simulate solvents. The results show that it is essential to include entropy effects in order to understand the observed trends. For instance, the equilibrium state in this case represents the state with lowest Gibbs free energy, as it must, but not the lowest enthalpy. The particular molecule is methyl 3-dimethylamino-2-cyanocrotonate (MDACC). The geometry at the carbon-carbon double bond can be either E or Z with roughly equal populations at ambient temperature. We have measured the equilibrium constant and the rates for the exchange between these states in a number of solvents: methanol, chloroform, acetonitrile, toluene, dichloromethane, acetone, and tetrahydrofuran. Furthermore, the N,N-dimethylamino group attached to the double bond also shows restricted rotation, and this has been measured in both the E and Z conformations. The equilibrium constant and the three rotational barriers provide excellent probes of the solvent effects. Electronic structure calculations with a number of basis sets up to the 6-311++G(2df,2p) level, using both Hartree-Fock and density functional (B3LYP) methods were used to predict the E and Z ground states, and the three transition states. The calculations were done for an isolated molecule and also for solvent models representing toluene, acetone, and ethanol. The E conformation is more stable in solution, is the structure in the crystal, and is also the prediction for the gas phase from the calculations. However, the dependence of the equilibrium constant on temperature shows that the Z conformation actually has lower enthalpy. The stability of the E conformation in solution must be due to entropic effects. Similarly, the solvent effect on the E-Z barrier is primarily due to entropy. The measured enthalpy of activation is similar in all the solvents, but the entropy of activation increases with the solvent polarity. The barrier to rotation of the N,N-dimethylamino group shows a combination of entropy and enthalpy effects. This combination of experiments and theory gives an extraordinarily detailed picture of solvent-solute interactions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Solvent Effects on Chemical Exchange in a Push–Pull Ethylene as Studied by NMR and Electronic Structure Calculations

et al. 2011

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Conformational and isomerizational studies of 3-N,N-dimethylhydrazino-2-acetyl propenenitrile using X-ray analysis, NMR and vibrational spectra, and ab initio calculations

Gróf

Gatial

Milata

et al. 2009

Journal of Molecular Structure

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Theoretical and Experimental Spectroscopic Analysis of Cyano-Substituted Styrylpyridine Compounds

Castro

Percino

Chapela

et al. 2013

IJMS

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A combined theoretical and experimental study on the structure, infrared, UV-Vis and 1H NMR data of trans-2-(m-cyanostyryl)pyridine, trans-2-[3-methyl-(m-cyanostyryl)] pyridine and trans-4-(m-cyanostyryl)pyridine is presented. The synthesis was carried out with an efficient Knoevenagel condensation using green chemistry conditions. Theoretical geometry optimizations and their IR spectra were carried out using the Density Functional Theory (DFT) in both gas and solution phases. For theoretical UV-Vis and 1H NMR spectra, the Time-Dependent DFT (TD-DFT) and the Gauge-Including Atomic Orbital (GIAO) methods were used, respectively. The theoretical characterization matched the experimental measurements, showing a good correlation. The effect of cyano- and methyl-substituents, as well as of the N-atom position in the pyridine ring on the UV-Vis, IR and NMR spectra, was evaluated. The UV-Vis results showed no significant effect due to electron-withdrawing cyano- and electron-donating methyl-substituents. The N-atom position, however, caused a slight change in the maximum absorption wavelengths. The IR normal modes were assigned for the cyano- and methyl-groups. 1H NMR spectra showed the typical doublet signals due to protons in the trans position of a double bond. The theoretical characterization was visibly useful to assign accurately the signals in IR and 1H NMR spectra, as well as to identify the most probable conformation that could be present in the formation of the styrylpyridine-like compounds.

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Conformational and isomerizational studies of 3-N,N-dimethylhydrazino-2-methylsulfonyl propenenitrile using NMR and vibrational spectra, X-ray analysis and ab initio calculations

Cited by 3 publications

References 29 publications

Solvent Effects on Chemical Exchange in a Push–Pull Ethylene as Studied by NMR and Electronic Structure Calculations

Solvent Effects on Chemical Exchange in a Push–Pull Ethylene as Studied by NMR and Electronic Structure Calculations

Conformational and isomerizational studies of 3-N,N-dimethylhydrazino-2-acetyl propenenitrile using X-ray analysis, NMR and vibrational spectra, and ab initio calculations

Theoretical and Experimental Spectroscopic Analysis of Cyano-Substituted Styrylpyridine Compounds

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