Synthesis and structural study of 2′‐ and 2′,6′‐positioned methyl‐ and nitro‐substituted 3‐(arylhydrazono)pentane‐2,4‐diones

Abstract

A systematic series of ortho‐methyl‐ and nitro‐substituted arylhydrazones 2–6 formed by Japp–Klingemann reaction between pentane‐2,4‐dione and the respective aryldiazonium salts have been synthesized and studied by X‐ray crystal structure analysis, with added quantum chemical calculations. The optimized molecular geometries based on DFT calculations, enabling determination of relevant rotational barriers, and the calculated bond and ring critical points, using the method of ‘atoms in molecules’, were found to correspond with the experimental data, involving specific molecular conformations and hydrogen‐bonded ring structure dependent on the ortho‐substitution, thus making possible reliable structural prediction of this compound class. Copyright © 2007 John Wiley & Sons, Ltd.

Quantum-chemical calculations, tautomeric, thermodynamic, spectroscopic and X-ray studies of 3-(4-fluorophenylhydrazone)pentane-2,4-dione

“…The X-ray diffraction, IR and NMR show that the studied compound presents in the same hydrazone structure in solid phases and in DMSO solution. The presence of one heterodienic system, HN-N]C-C]O, forming a fairly weak heteronuclear RAHB, N-H/O, has been supported by crystallographic data, and length of this distance N/O 2.5872(12) Å falls in the middle of the N/O distances range, 2.538-2.597 Å, as observed in previous studies on b-diketo-arylhydrazones [28]. This might be useful in the design of functional materials attributed to smart hydrogen bonding [6][7][8][9][10][11], photo-triggered structural switching [43], and targeted metal ion complexes [1][2][3][4][5][13][14][15].…”

“…Here, it is possible to see that N-H/O, H-bond found in HL, with N/O distance, 2.5872(12) Å, falls in the middle of the N/O distances range, 2.538-2.597 Å, as observed in previous studies on b-diketo-arylhydrazones [28]. Comparatively, this suggests that the 4-F group, s p ¼ 0.06, located far from the N-H/O center, may be causing an efficient shortening of the N-H distance.…”

Structural and thermal properties of three cyano-substituted azoderivatives of β-diketones

“…The two carbonyl bond distances are slightly different [1.231(3) and 1.212(3) Å], the longer one concerning the intramolecular hydrogen bonding involving its oxygen atom (see Fig. 2 and its footnote), where the donor(N)Á Á Áacceptor(O) distance of 2.567(2) Å falls within the range (2.50-2.62 Å) observed for other studied ADBs [7,8,14,22,26].…”

“…The negative entropy of activation suggests that decomposition is slow [30]. The values of the pre-exponential factor in the Arrhenius equation (A) are within the 3.7-2.4 Â 10 5 s À1 range, thus not allowing to establish the molecularity of the reaction [26][27][28]. The sharp thermal decomposition threshold and the high mass loss rate of HL 1-3 make them good candidates for optical recording media [31,32] or optical sensors [33], although experiments with polarized light indicate that they do not possess liquid crystal properties under the studied conditions, in contrast to related compounds [34].…”

Synthesis and Structural Characterisation of New Bifunctional o-Hydroxyacetophenones – Potential Linker Molecules for Coordinative Framework Construction

“…Instead, the C=O units of the acetyl groups are sandwiched at a distance of ca. 3.2Å between the aromatic rings of adjacent molecules, which suggests the presence of π(C=O) · · · π(arene) interactions [34]. The molecules are associated by a close network of C-H···O hydrogen bonds [35] .…”