Benzamidoximes. II. A 15N NMR study

Experimental and theoretical investigations of 4-chloro-N-(2-methoxyphenyl)benzamidoxime

4-Chloro-N-(2-methoxyphenyl) benzamidoxime (CMB) has been synthesized and characterized by X-ray diffraction, (1)H NMR, (13)C NMR, FT-IR and FT-Raman spectra. The X-ray study showed that CMB has a Z configuration, due to the strong intramolecular N-H···O hydrogen bond and centrosymmetric dimer form due to intermolecular O-H···N' and O-H···O' hydrogen bonds. The 2-methoxyphenyl and 4-chlorophenyl rings are twisted from the mean plane of the hydroxyamidine group by 33.09 (1) and 44.89 (1)°, respectively. The optimized molecular structure and vibrational frequencies have been calculated with DFT (B3LYP) method by using a 6-311G(d,p) basis set. The (1)H and (13)C NMR chemical shifts were calculated by the gauge-including atomic orbital (GIAO) method with the B3LYP/6-311G (d,p) level. A comparison between experimental and calculated theoretical results indicate that the density functional B3LYP method provided satisfactory results for predicting IR, Raman, (1)H NMR and (13)C NMR spectra properties.

Theoretical analysis of solvent effects on nitrogen NMR chemical shifts in oxazoles and oxadiazoles

Using quantum chemistry methods we have evaluated the solvent effects on the (14)N NMR chemical shifts in five oxa- and oxadiazoles dissolved in twelve solvents. These solvents differ in their polarity with the dielectric constants varying from 2 to 80. Moreover, three of them have a hydrogen-bond donor character. All possible hydrogen-bonding in the water solution with the oxygen and nitrogen (hydrogen-acceptor) centers in oxazoles (2) and oxadiazoles (3) have been considered in our studies. It has been shown that both the pure solvent and hydrogen-bonding effects are significant and result in (14)N magnetic shielding increase. In water solutions the pure solvent effect is larger than the hydrogen-bonding effect. In addition, the solvent effect has been analyzed in terms of its direct and indirect contributions. It should be emphasized that our theoretical results for (14)N chemical shifts in oxa- and oxadiazoles remain in a very good agreement with the accurate experimental data.

(1)H, (13)C, (15)N NMR and (n)J(C, H) coupling constants investigation of 3-piperidino-propylamine: a combined experimental and theoretical study

Proton coupled and decoupled (13)C, (1)H, (15)N, DEPT, COSY, HETCOR and INADEQUATE NMR spectra of 3-piperidino-propylamine (3-pipa) have been reported for the first time. In order to provide a precise structural elucidation, the magnitude of (n)J(C, H) (n=1, 2, 3) coupling constants of 3-pipa (C(8)H(18)N(2)) have been determined. Solvent effects on chemical shifts have been investigated by using CDCl(3) and DMSO. Molecular mobility of the title molecule has also been investigated by performing (13)C NMR spin-lattice relaxation time (T(1)) measurements. (13)C, (1)H and (15)N NMR chemical shifts and (1-3)J(C, H) coupling constants of 3-pipa have been calculated by means of B3LYP density functional method with 6-311++G(d,p) basis set. Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.