The chemistry of N,N′-dimethylformamidine. III. Tautomerism and hindered rotation
- 1 June 1978
- journal article
- Published by Canadian Science Publishing in Canadian Journal of Chemistry
- Vol. 56 (11) , 1470-1476
- https://doi.org/10.1139/v78-240
Abstract
Proton nmr and infrared studies of neat N,N′-dimethylformamidine (DMFA) have shown that the cis isomer 1 is present exclusively and that it undergoes tautomerism. At 25 °C, ktaut = 8.2 × 102 s−1, Ea = 41.5 ± 1.5 kJ mol−1, ΔH≠ = 39.1 ± 1.5 kJ mol−1, and ΔS≠ =−57.5 ± 5.0 J mol−1 K−1. The tautomerism is proposed to occur through a hydrogen-bonded cyclic dimer. The effects of solvent on the tautomeric rate in DMFA have also been investigated for CD3NH2 and CDCl3 solutions.Potassium N,N′-dimethylformamidide (PDMFA) in CD3NH2 does not exhibit hindered rotation about the single C—N bond on the nmr lime scale over the temperature range −56 to 25 °C. However, protonated DMFA undergoes hindered rotation about this bond in highly acidic media (97 wt.% H2SO4 at 25 °C, krot = 0.16 × 102 s−1, Ea = 35.4 ± 0.8 kJ mol−1). The acid catalysis is interpreted as occurring through formation of the diprotonated species. The two nitrogens in protonated DMFA have different base strengths.Keywords
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