Sarjit Kaur, Sean Boley, Miriam Rossi, and Nikoleta Tsvetanova. Vassar College, Poughkeepsie, NY
Intermolecular interactions of a potential amide mimic, N-methyl-2,2-dicyanovinyl benzene (A), were studied in chloroform using 1H NMR and FTIR spectroscopy, and X-ray crystallography. A new band at 3265 cm-1 appeared on FTIR spectra when the concentrated was increased from 1 mM to 15mM, indicating involvement of NH in hydrogen bonding as compound A self-associates. The NH was found shifted to slightly higher ppm (from 6.29 to 6.89) with increasing concentration. Both results clearly showed NH as the proton donor. However, the proton acceptor site was more difficult to identify. Although the cyano group is expected to be involved, there was no change in the cyano band by FTIR spectroscopy when the concentration was changed from 1mM to 50mM. X-ray crystallography was used to determine the structure of A crystallized from chloroform to identify the proton acceptor. Given that the intermolecular studies were carried in a relatively low dielectric constant solvent, the X-ray data could be extrapolated to understand how A may self-associate through hydrogen bonding interactions in chloroform. The crystallography data was definitive in identifying the nitrogen atom of the cyano group as the proton acceptor. A hydrogen bond between -NH----NC- was identified with a bond length 2.25 A, which is consistent with hydrogen bonding lengths. Based on previous reports of enaminonitrile (and nitriles) interactions in protic polar solvents, a further inference can be made that the hydrogen bond acceptor site is the lone pairs of the nitrogen, rather than the pi electrons of the C-N triple bond.
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