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

Abstract

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 Å3, Dx = 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.

Weak C-H…O hydrogen bonds in alkaloids: An overview

“…N5-C13 and N5-C14, are in agreement with the standard value (Allen et al 1987). The length of the bond N5-C13 is close to the values obtained in E-and Z-isomers of 1-(2amino-1-cyano-2-thioethylene) pyridinium-ylide (Fischer et al 1983). The C9=O3 bond length [1⋅255(2)Å] is greater than its theoretical value [1⋅199Å] and it may probably be due to the strong intramolecular O2-H17…O3 hydrogen bond.…”

A comparative X‐Ray diffraction study and MO AM1 semi‐empirical calculations on the 1‐carbethoxymethyl‐4 triazolium‐4′nitrobenzoyl‐2″,3″,4″ trinitrophenyl methylide

“…The analysis of the Cambridge Crystallographic Database System [4][5][6][7][8][9][10][11][12][13][14] shows that among 160 000 structures of organic and organometallic compounds, only nine structures corresponds to cycloimmonium ylides. Thus, it appears very important to increase the number of crystallographic structures resolved by X-ray diffraction in order to elucidate the spatial distribution between the carbanion and the heterocycle in cycloimmnium ylides.…”