Two different products from the reaction of 1-aryl-5-chloro-3-methyl-1H-pyrazole-4-carbaldehyde with cyclohexylamine when the aryl substituent is phenyl or pyridin-2-yl: hydrogen-bonded sheetsversusdimers

Cyclohexylamine reacts with 5-chloro-3-methyl-1-(pyridin-2-yl)-1H-pyrazole-4-carbaldehyde to give 5-cyclohexylamino-3-methyl-1-(pyridin-2-yl)-1H-pyrazole-4-carbaldehyde, C16H20N4O, (I), formed by nucleophilic substitution, but with 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde the product is (Z)-4-[(cyclohexylamino)methylidene]-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one, C17H21N3O, (II), formed by condensation followed by hydrolysis. Compound (II) crystallizes withZ′ = 2, and in one of the two independent molecular types the cyclohexylamine unit is disordered over two sets of atomic sites having occupancies of 0.65 (3) and 0.35 (3). The vinylogous amide portion in each compound shows evidence of electronic polarization, such that in each the O atom carries a partial negative charge and the N atom of the cyclohexylamine portion carries a partial positive charge. The molecules of (I) contain an intramolecular N—H...N hydrogen bond, and they are linked by C—H...O hydrogen bonds to form sheets. Each of the two independent molecules of (II) contains an intramolecular N—H...O hydrogen bond and each molecular type forms a centrosymmetric dimer containing oneR22(4) ring and two inversion-relatedS(6) rings.

13C-NMR spectra of benzenesulphonyl derivatives

13C-NMR chemical shifts and 1J(CH) and 3J(CH) coupling constants have been determined for a series of C6H5SO2X derivatives (X = Cl, C6H5, Ona, OCH3, OC2H5, OC6H5, NH2, NHNH2, N(CH2)5, NHC6H5) in hexadeuteriodimethyl sulphoxide solutions, and the substituent shift values of benzene nucleus have been calculated for the individual SO2X groups,. These groups, carrying partial positive charge at the sulphur atom, have electron-acceptor effects on the benzene nucleus, and increasing electron-donor character of the substituent X is connected with a proportional increase of mesomeric acceptor influence on the benzene nucleus and with increase in absolute values of 1J(CH).

Binary Dioxygen Complexes of Nickel, Palladium, and Platinum, M(O2) and (O2)M(O2), in Low Temperature Matrices

The cocondensation reactions of nickel, palladium, and platinum atoms with gaseous oxygen or dilute oxygen–argon mixtures at 4.2–10 °K give rise to binary transition metal dioxygen complexes. Variable concentration and diffusion controlled warm up studies, 16O/18O isotopic substitution studies, normal coordinate and isotope intensity calculations establish the complexes to be of the types M(O2) and (O2)M(O2). Both the mono- and bisdioxygen complexes contain the dioxygen molecules coordinated to the metal atom in a side-on fashion, with a unique D2d "spiro"-type structure favored for the bis-complexes. Frequency and bond stretching force constant trends within the series of complexes are examined and suggest that the O—O and M—O values increase with increasing coordination number, and thus with an increase in partial positive charge on the metal. This trend in O—O stretching frequencies is not in accord with the evaluation of metal–dioxygen bond strengths as based on the degree of reversibility of dioxygen coordination.