p-Dimethylaminobenzaldehyde 4,5-Diaza-9-fluorenylidenehydrazone Monohydrate

Synthesis, conformational analysis, and spectroscopic characterization of peptides based on Daf, the first rigid transition‐metal receptor, cyclic Cα,α‐disubstituted glycine

“…Bond lengths and bond angles are in general agreement with previously reported values for the geometry of the tert ‐butyloxycarbonylamino37 and ester groups,38 the peptide unit,39, 40 the Aib residue,41, 42 and the 4,5‐diazafluorene moiety 14, 43. In particular, the (sp 2 )C—C(sp 2 ) bond, directly connecting the two pyridyl rings (in the range 1.45–1.46 Å), is typical of the 4,5‐diazafluorene system,14, 43 and the two (sp 3 )C α —C β (sp 2 ) bonds (in the range 1.51–1.54 Å) are reminiscnent of the corresponding bonds in the benzyl moiety 44. Preliminary evidence for the presence of the strain introduced by the fully extended (C 5 ) structure45, 46 in the Daf residue of Boc–Aib–Daf–Gly–OMe is provided by the value of the conformationally critical N—C α —C′ (τ) bond angle,39, 40, 45 104.9(3)°, very much compressed if compared to the tetrahedral value (109.5°).…”

“…An additional intermolecular H‐bond is present in the structure, (peptide) N3— H · · · N δ1 (pyridine) (− x + 1, − y + 2, − z ) with a N3 · · · N δ1 · · · distance of 2.949(5) Å. As also stated for previously solved x‐ray diffraction structures of 4,5‐diazafluorenyl compounds,14, 43 it is worth mentioning that the formation of a H‐bond with a nitrogen atom as acceptor is quite peculiar, particularly when more electronegative carbonyl oxygens are available. It is also evident that for the two nitrogen atoms of the pyridyl moiety the charge concentration is greater on one (N δ1 in this case) than on the other.…”

“…In these Daf compounds some very large bond angles at sp 2 carbons (130°–131°) are also found: C α —C β1 —C γ11 and C α —C β2 —C γ21 (with C γ11 and C γ21 external to the cyclopentadienyl ring). The bond angles centered at the sp 2 nitrogen atoms of the pyridyl rings have values in the usual range (113°–116°) 14, 43…”

p-(Dimethylamino)benzaldehyde Isonicotinoylhydrazone Monohydrate

“…(Johnson, 1976) plot of the title compound with the atom-numbering scheme. It can be seen that the molecule is in the keto tautomeric form and that the configuration of the N3--C7 bond is E. The bond lengths and angles in the pyridine and dimethylaminophenyl rings are in agreement with those of related structures reported earlier (Wang, Deng, Wu &Chen, 1992;Lu et al, 1995). While the hydrazone moiety is in the plane of the phenyl ring, the pyridine ring makes an angle of 48.08 (7) ° with the phenyl ring, and the dimethylamino group is tilted 4.3 (2) ° from the plane of the phenyl ring.…”

4,5-Diaza-9-fluorenone Isonicotinoylhydrazone Monohydrate

“…The two other major hydrogen bonds, N4--H4N...O1W and C15--H15..-O1, form the interlayer connections. We have observed previously that due to the possibility of different charge concentrations between the two pyridinyl N atoms of the diazafluorene moiety, the one with the greater charge is involved in the stronger intermolecular hydrogen bonds, whereas the other may be involved in only a weak interaction (Fun, Sivakumar, Zhu & You, 1995;Lu et al, 1995). In the title structure, the same pattern is observed; the N2 atom is involved in a strong O---H...N (O1W...N2) contact, while the N1 atom has a very weak interaction with the C17 atom in the form of a C--H...N contact.…”