Stereochemische Untersuchungen heterocyclischer Verbindungen. XII. Kristall- und Molekülstruktur von 1-(2-Amino-1-cyano-2-thio-ethylen)pyridiniumyliden

Stereochemical Investigations of Heterocyclic Compounds. XII. Structural Investigations of 1-(2-Amino-1-cyano-2-thio)ethene Pyridinium Ylides Two isomerization processes were found by ¹H-d-n. m. r. characterized by ΔG^* = 67 ± 4 KJ/mol for E- Z-isomerization and ΔG^* = 46 ± 5 KJ/mol for the hindered rotation of the pyridine substituent in 1a . The structure of 1b was solved by direct method. Crystals are monoclinic space group P2₁/n, a = 13.682(3), b = 9.452(1), C = 19.713(6) Å, β = 96.42(2)°, V = 2533.3 ų, D_x = 1.328 Mg · m⁻³, Z = 8. Both E- and Z-isomeres of 2b are found in the crystal lattice. The amino C distance with 1.369 (1,387) Å is shorter than the theoretical single bond distance. The formal  CC double bond with 1.377 (1.391) Å is considerably longer than 1.337 Å observed in the some alkenes.