Can. J. Chem. 58, 1372 (1980. Thermodynamic parameters for the self-association of N-methylformamide and N-methylacetamide in CCI, solvent have been determined by infrared spectroscopy. The pure base calorimetric method was used to determine the enthalpy of hydrogen bond complex formation of N-methylformamide and N-methylacetamide with N,N-dimethylformamide, N,N-dimethylacetamide, ethyl acetate, and dioxane. Comparison of the calorimetric and spectroscopic results show that the dimers of N-methylformamide and N-methylacetamide are linear with hydrogen bond enthalpies of -2.9 and -3.9 kcal mol-' respectively. The carbonyl group of N-methylacetamide was found to be a better proton acceptor than the carbonyl of N-methylformamide in agreement with theoretical predictions. N-methylacetamide was found to be a better proton donor than N-methylformamide in disagreement with theoretical predictions. The dimer self-association constants appear to be larger than previously reported.
We investigated the degree to which strength of pulmonary hypoxic vasoconstriction affects perfusion of pulmonary shunt pathways in acute atelectasis. In 17 intact supine dogs (anesthetized, paralyzed, and ventilated) we produced left lower lobe atelectasis by occluding the lobar bronchus during oxygen inhalation. Subsequently, shunt fraction (reflecting perfusion of that lobe) was measured using an SF6 infusion while the dogs breathed room air; the mean was 26% (range 14-40%). Pulmonary pressor response to hypoxia was assessed in 13 dogs using the increase in pulmonary end-diastolic gradient (PDG) produced by inhalation of 10% oxygen. Those animals with the largest increase in pulmonary diastolic gradient had the smallest shunt fraction while breathing room air, whereas those with the smallest response had the largest shunt fraction. The contribution of local hypoxia to vasoconstriction in the shunt pathway was assessed in 13 dogs breathing room air by measuring the increase in shunt fraction produced by infusing prostaglandin E1 (PGE1). Those with the largest increase in shunt fraction had the smallest pre-PGE1 shunt fraction. Thus the strength of pulmonary vascular reactivity to hypoxia markedly influences the degree of vasoconstriction in shunt pathways and is a major determinant of shunt pathway perfusion.
The rate constants for benzene and toluene were found to be nearly equal In any given alcohol except methanol, for which the experimental scatter was large. We have therefore taken the average value, k1 = 1,3 X 106 M"1 s'1, for both benzene and toluene in methanol at 299 K. (23) E.
The pure-base calorimetric method has been used to determine enthalpies of formation for hydrogen-bonded complexes of pyrrole, indole, and imidazole with various bases. These enthalpies are compared to those obtained by other methods. Frequency shifts determined in CC14 solvent have been used to findrelationships for N-H-O and N-H-N adducts. From these relationships, hydrogen-bond enthalpies have been calculated for bases not determined by the pure-base method. The systems investigated have been used as models to calculate enthalpies of formation for the more complex nucleic acid base pairs. Comparison of enthalpies calculated from the model compounds is made to enthalpies determined by theoretical and other experimental methods.
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