Substituent Effect of N,N-Dialkylamides on the Intermolecular Hydrogen Bonding with Thioacetamide

Abstract

The alkyl substituent effect on the intermolecular hydrogen-bonding properties of tertiary amides has been investigated experimentally and theoretically. N, N-Dimethylformamide (DMF), N,N-diethylformamide (DEF), N,N-diisopropylformamide (DIF), N,N-dimethylacetamide (DMA), N,N-diethylacetamide (DEA), and N,Ndiisopropyl acetamide (DIA) were chosen as proton acceptors for thioacetamide (TA) in CCl 4 solution. Thermodynamic parameters for the interaction of tertiary amides with TA have been measured by nearinfrared (NIR) absorption spectroscopy. For DMF, DEF, and DIF, the standard enthalpy change of 1:1 hydrogen-bonded complex formation is about -19.5 kJ/mol and the equilibrium constant at 298 K is about 60 M -1 . For DMA, DEA, and DIA, the standard enthalpy change increases from -18.9 to -19.8 kJ/mol and the equilibrium constant at 298 K decreases from 65 to 50 M -1 , as the alkyl group becomes bulky. The IR data of N-H stretching vibrations of TA are very consistent qualitatively with the NIR thermodynamic data. The temperature dependence of proton NMR chemical shift has been examined for N-Hs of TA to understand the characteristics of hydrogen bonding. We suggest that more hydrogen-bonding interaction via the hydrogen syn to the sulfur atom of TA could take place in the formamide series, compared to the acetamide series. The proton affinity of these tertiary amides is calculated by using HF/6-31+G*, HF/6-31G**, and B3LYP/ 6-31G** levels of ab initio molecular orbital theory.

Densities and volumetric properties of (acetonitrile+an amide) binary mixtures at temperatures between 293.15K and 318.15K

“…Also, the V E m values are more negative for ACN + DMA than those for ACN + DMF. This is due to the fact that electron density at oxygen atom of the carbonyl atom of DMA is greater than that of DMF [2,32] due to the presence of -CH 3 group at the carbon atom carbonyl group in DMA, resulting in stronger interactions in (ACN + DMA) system. Another contribution to negative V E m comes from the fitting of small ACN molecules (molar volume = 52.845 cm 3 AE mol À1 at T = 298.15 K) into the voids created by three-dimensional hydrogen bonded network of FA molecules [33] and into the voids present in bigger DMF/NMA/DMA molecules (molar volumes: DMF = 77.3767 cm 3 AE mol À1 , NMA = 76.5982 cm 3 AE mol À1 , DMA = 93.0272 cm 3 AE mol À1 at T = 298.15 K).…”

Theoretical Characterization of Hydrogen Bonding Interactions between RCHO (R = H, CN, CF3, OCH3, NH2) and HOR′(R′ = H, Cl, CH3, NH2, C(O)H, C6H5)

“…Similar inference has also been drawn by Kim et al in their study on substituent effect of N,Ndialkylamides on intermolecular hydrogen bonding with thioacetamide in CCl 4 solvent using theoretical and experimental techniques. 85 Their studies showed that stability of the hydrogen-bonded complex between thioacetamide and amides had increased with increase in electron-donating alkyl group. The HB acceptor ability have often been linked to proton affinity of that site.…”

Thermodynamic and Acoustic Study on Molecular Interactions in Certain Binary Liquid Systems Involving Ethyl Benzoate

“…The electron density at oxygen atom of the carbonyl atom of DMAc is greater than that of DMF due to the presence of methyl group at carbon atom of carbonyl group in DMF resulting in stronger interaction in thesystem [39,40]. The values of ethyl benzoate + DMA are in between these two.…”