Imidazole thermodynamic data

This chapter is an update to Chapter 8.04 of CHEC-II(1996) <1996CHEC-II(8)95> it covers the literature from 1995 to 2007. More specifically, it contains major informations on the preparation and reactivity of these bicyclic 5-5 systems. Furthermore, a variety of biological activities and important applications in the chemical, medical, and agrochemical field beyond the scope of this chapter. Considering the little information obtained in few areas, coverage of sections dealing with structural, theoretical and thermodynamic data has been kept to a minimum since only imidazo[l,2- ]imidazole and imidazo[l,2- ]pyrazole systems have been the subject of recent studies. The most important structural data have already been summarized in CHEC-II(1996), Chapter 8.04. 

Stability constant measurements have shown that imidazoles form some of the most stable complexes of all N-heterocyclic ligands. Some thermodynamic data are given in Table 12. 

Table 12 Some Thermodynamic Data for the Formation of Silver(I) Imidazole Complexes...

Suszka538 has reported spectroscopic and thermodynamic data on the association of imidazole-2-thiones and 7V,tV -dialkylthioureas with SO2 in a variety of solvents. 

Significant i.r. frequency shifts in N—H mode have been observed in ML, C2 complexes [M = Co or Ni L = 5-aminoimidazole X = Br, I, NO3, MeC02, NCS, and S04 m = 1,2, or 4). Thermodynamic data have been obtained for the reaction of imidazole and x-methylimidazole (x = 1,2,4, or 5) with aquocobaltamine in aqueous solution. The complex [(tren)Co(/i-peroxo-/t-hydroxo)Co(tren)](C104)3,3H20 has been prepared by the oxygenation of [Co(trenXH20)2] in alkaline solution. ... 

Spin-crossover kinetics for Fe(II) complexes have been reviewed, and enthalpies, entropies, and rate constants for a range of Fe(II) and Fe(III) spin-crossover complexes documented. Thermodynamic and kinetic parameters, iron-ligand bond distance and volume changes, and calorimetric data relating to the low-spin/high-spin transition in solution and in the solid state obtained prior to 1991 have been fully documented and discussed. A selection of thermodynamic and kinetic parameters for the spui-crossover complexes of 2-(2-pyridyl)imidazole (pyim) and A-(2-pyridylmethyl)picolinamidine (ppa), tetrakis(2-pyridylmethyl)-/rani-l,2-cyclohexanediamine (tpchxn), 3-(1,10-phenanthrol-2-yl)-5-methyl-1,2,4-oxadiazole (phen-... 

Comprehensive spectral analysis including solid state FTIR, solid state Raman, and solid state C NMR by Raghavan et al. (1993), resulted in the following conclusion, particularly from sohd state C NMR ... spectral characteristics of Form I were interpreted in terms of the presence of more than one orientation for the n-butyl side chain and the imidazole ring. In addition, the spectral characteristics of Form II were consistent with a large molecular motion of the n-butyl side chain. Although spectral differences were observed, no conclusions about relative thermodynamic stabihty could be or were made from the spectral data, leaving those conclusions to the more traditional methods of thermal analysis (DSC) and solubihty measurements. 

The IR spectra of 3-oxo-l-thioxo-2,3-dihydro-17/-pyrrolo[l,2-c]imidazole in the solid form and in solution have been measured as a function of temperature, and a direct correlation has been obtained between the two phases and the type and extent of hydrogen bonding. It was suggested that the compound exists as cyclic dimer (103) in the solid state (below 310 K) and in dilute solution by formation of two equivalent hydrogen bonds. At transition temperature, the cyclic dimer changes to the noncyclic dimer (104) and persists in this structure till 410 K. In addition, thermodynamic functions AG°, AH", and AS" have been estimated using spectral data in solution <84CJC1845>. 

Other Physical Properties.—Conformational information for thiols and sulphides can be obtained from enthalpy of formation data. Proton-transfer of benzyl-mercaptan (protonation at sulphur with CF3SO3H, and de-protonation by imidazole) has been studied. Thermodynamic parameters for acidity constants of substituted benzenethiols, and for hydrogen-bonding interactions between alkanols and di-n-octyl sulphide and the analogous ether and N-methylamine, reveal a dominant electronic influence of the orM<>-substituent, and substantially higher hydrogen-bond acceptor ability for the aliphatic sulphide than is generally assumed. ... 

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