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Applications of Sensors to Physical Measurements
Published in Robert B. Northrop, Introduction to Instrumentation and Measurements, 2018
Didenko et al. speculated that the lineless SBSL emission in water is (1) due to the summation of broadened emissions from multiple molecular and atomic sources and (2) brems-strahlung emission from partial ionization of the heated gas within the bubble. Didenko et al. studied the SBSL emission spectra from a variety of polar aprotic liquids (cf. Glossary), including formamide, N-methylformamide, N,N-dimethylformamide, 1,2-diaminoethane, dimeihylsulfoxide, and adiponitrile. They subdivided their results into emissions from bubbles held stationary in the sound field and bubbles that move around the reaction flask’s center and emit photons. The spectra from the moving bubbles in methylformamide and adiponitrile showed a broad emission line at ca. 380 nm that was from –CN dissociated from the liquid molecules. When DMSO was used, there obviously was no –CN line to dissociate (no N in the molecule), but there also were no band emission lines from S2, –SO, or SO2, which were expected. There were no lines from liquids with stationary bubbles, presumably because the intense blackbody bremsstrahlung radiation intensity swamped them.
Amidation of Methyl Esters with Formamides in the Presence of KCN as the Catalyst
Published in John R. Kosak, Thomas A. Johnson, Catalysis of Organic Reactions, 2020
A. Benderly, L. Y. Dennis, A. Bravo
No reaction, however, takes place when N,N-dimethylformamide is employed. Similarly, sodium methoxide promotes the exchange reactions between methyl esters and formamide or N-methylformamide but not with N,N-dimethylformamide [7,8]. This suggests that the amidation reaction, catalyzed by either sodium methoxide or potassium cyanide, may have a common mechanism. In both cases, the catalysts behave as bases, generating formamide (N-methylformamide) anions, the actual reactive species in the system [7].
The liquid structure of the solvents dimethylformamide (DMF) and dimethylacetamide (DMA)
Published in Molecular Physics, 2019
N. Basma, P. L. Cullen, A. J. Clancy, M. S. P. Shaffer, N. T. Skipper, T. F. Headen, C. A. Howard
A major focus of interest in the literature concerns the intersolvent hydrogen bonding that occurs, particularly in the case of DMF. Formamide (FA, R2/R3 = H) and N-methylformamide (NMF, R2 = H, R3 = CH3), of which DMF is a derivative, are both protic solvents and can therefore act as both proton donors and acceptors via their N–H and C=O groups, respectively, and are consequently able to form C=O—H–N hydrogen bonds (H-bonds). Neutron diffraction studies have revealed the existence of this H-bonding network in the liquid structures of both FA and NMF. FA comprises a structure dominated by large cyclic clusters, with each molecule participating in exactly two H-bonds cooperatively arranged in a ring [31]. The preferred nearest neighbour orientation of two molecules is such that the C–N bonds of neighbouring molecules sit anti-parallel [32], forming strong directional C=O—H–N bonds at 1.95 Å. As for its derivative, N-methylformamide (NMF), the findings point to very stable dimers and ‘linear’ trimers leading to a chain-like structure stabilised by weak H-bonds. Interestingly, however, the prevalence of these C=O—H–N H-bonds has been found to be greater in NMF than in FA [33].