Structural Studies of the Bisimidazole 5,5-Dimethyl-1,3,2-Dioxaphosphorinane-2-Thioxo-2-Hydroxy Complex

Abstract

The molecular complex of imidazole (Im) with 5,5-dimethyl-1,3,2-dioxaphosphorinane-2-thioxo-2-hydroxy acid (DPTHA) involves strong (O-H‚‚‚H and N .. H + ‚‚‚N) and weak (C-H‚‚‚O and C-H‚‚‚S) hydrogen bonds and has an unusual molecular packing. The crystals are monoclinic, space group I2/m, with a ) 10.609 (5) (000) ) 672, and µ ) 2.760 mm -1 . A comparison of 13 C CP/MAS NMR data for imidazole and the Im‚‚‚H + ‚‚‚Im cation shows that the 13 C isotropic chemical shifts of the C4 and C5 carbons, and of the δ 22 and κ parameters for C2 carbons for each compound are different. GIAO calculations at the HF/6-311 + G(2d,p)//B3LYP/6-31G* level reveal correlations between the differences in the 13 C chemical shift between the C4 and C5 atoms, the values of δ 22 and κ for the C2 carbon, and the N‚‚‚H + distance. An analysis of 13 C chemical shift parameters provides information about the strength of the hydrogen bonds and the localization of the proton in the N‚‚‚H + ‚‚‚N linkage.

Comparison of the proton-transfer path in hydrogen bonds from theoretical potential-energy surfaces and the concept of conservation of bond order. II. (N—H...N)+ hydrogen bonds

“…This is unexpected as in the case of double minima the H atom is often statistically distributed between the two minima around the symmetry centre, resulting in two halfhydrogen atoms in a diffraction study. However, in the present cases there is a large uncertainty in the hydrogen positions and furthermore the refinements of the X-ray data are not (a) LEQHIY: Bis(imidazole) 2-hydroxy-5,5-dimethyl-1,3,2-dioxaphosphorinane-2-sulfide; space group I2/m (Potrzebowski et al, 1998). Contour levels : 1, 2, 4, 8, 13, 21, 42, 63, 84, 125 kJ mol À1 (0.25, 0.50, 1, 2, 3, 5, 10, 15, 20 and 30 kcal mol À1 ).…”

Modulating the Strength of Hydrogen Bonds through Beryllium Bonds

“…These modulation effects on the strength of inter- and IMHBs by beryllium bonds can be viewed also under the perspective of the positive charge-assisted hydrogen bonding, , which reflects the close relationship between hydrogen bonding and protonation . It is known for instance, both experimentally − and theoretically ,, that upon protonation the HB in both imidazole dimer and malonaldehyde becomes significantly reinforced, the proton sitting near the midpoint of the two heteroatoms. The formation of the beryllium bond implies a similar mechanism in which the charge transfer goes to the Be system rather than to an incoming proton.…”

Protonation and phase effects on the NMR chemical shifts of imidazoles and pyrazoles: experimental results and GIAO calculationsElectronic supplementary information (ESI) available: absolute and relative shieldings calculated at the B3LYP/6-311++G**//B3LYP/6-311++G** level for compounds V to XXI as well as pyrazole and 3,5-dimethylpyrazole dimers, trimers and tetramers (420 shieldings). See http://www.rsc.org/suppdata/nj/b2/b210251j/

“…Protonation of a base B having a lone pair normally affords the cation [B-H] + but in some cases this hydrogen cation binds to another B molecule to form a [B-HÁ Á ÁB] + structure, such as I in the case of B being imidazole. 10,27 Pyrazolium and imidazolium cations If a solution of azole is dissolved in a medium containing a strong acid and the solvent evaporated an azolium salt is obtained in most cases. In this way, using hydrochloric, hydrobromic and trifluoroacetic acids, the compounds reported in Scheme 2 have been prepared (compound 6c was fortuitously obtained while trying to prepare 2).…”

“…Using eqns. (10) and (11) to transform s into d, the following equation is obtained, where both nuclei are considered in the same equation:…”