Microwave Absorption and Molecular Structure in Liquids. LIII. Hydrogen Bonding and Dielectric Properties in Chloroform Mixtures

Abstract

DiscussionThe model and approximations are obviously too crude to lend significance to exact values of parameters deduced above and to support quantitative interpretations of the interactions they represent. Several important conclusions of a qualitative nature find solid basis nevertheless in the comparison of calculations with experiment .The inadequacy of the independent bond approximation has been demonstrated through its failure to account for values for (r2)oln12 as large as observed. Exclusion of g i g r neighbor pairs about both Si and 0 raises this ratio into the range of the experimental results. The positive temperature coefficient admits of explanation only by assignment of u < 1. Complete exclusion of all g * g r sequences tends to over-estimate either the temperature coefficient or the magnitude (r2)o/n12. Guided by structural considerations, we achieve a more refined agreement with experiment by relaxing the exclusion of such sequences about 0 (but not about Si), adopting 6 S 0.06 to this end.The main conclusions, namely, that g i g r sequences are largely suppressed and that the trans state is preferred over the gauche ( u < l ) , are firmly established by the foregoing analysis. The calculations in support of these conclusions are insensitive to minor changes in 8' or other structural parameters. The idealization implicit in the model whereby discrete rotational states are substituted €or averages over ranges of angle may distort the calculations in detail, but could scarcely affect our principal conclusions to a significant degree. The former of these conclusions finds independent basis in the structure. The latter confirms that nonbonded methyl groups attract a t a distance of about 3,s A,; no other grounds for the preference of the trans state over the gauche is apparent.A value of Acr in the range 500 to 1000 cal. mole-' accords with structural considerations presented earlier.According to the numerical calculations (Table I), A E~ S 2000 cal. mole-', which is twice the estimate for this quantity on the basis of coulombic repulsion between oxygen atoms. The sensitivity of numerical calculations (Fig. 4) to the value of 6 suggests that this parameter (and therefore A Q also) is subject to greater error than is u from idealizations underlying the calculations. The discrepancy is well within the limits of error in either the model or in the experimental results.If the suppression of g*gr sequences about 0 is indeed to be accounted for by coulombic repulsions, a decrease in the polarity of the medium should further diminish 6. To the extent that u also is influenced by electrostatic efiects associated with the slightly closer proximity of the pairs of atoms, Si and 0, separated by three bonds in the chain (see above), it should increase with decrease in polarity of the medium. Both changes should increase (r2)o/nZ2. Results for the fluorocarbon mixture,28 in which (r2)o 'nlz was found to be 7.7, are qualitatively in accord with this deduction.A satisfactory account of the spatial configurations o...

Far-infrared absorption spectra of water, ammonia, and chloroform calculated from instantaneous normal mode theory

“…The calculated Debye times of 5.3 ps ͑H 2 O͒, 0.62 ps ͑NH 3 ), and 5.1 ps ͑CHCl 3 ) are all close to values experimentally derived from frequency-dependent complex dielectric constants of these liquids. 7,32,33 These Debye times are not affected by the inclusion of polarizability in the analysis, indicating that relaxation of the electronic polarization ͑which can occur through translational as well as orientational motion͒ is occurring on the same time scale as reorientation of the permanent dipoles. Better statistics will be required to determine whether the liquid models show secondary dielectric relaxation processes, as observed experimentally 7, 33 and in simulations with a different potential 28 in the case of water.…”

Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

“…Figure 1.7 gives relaxation frequency range for classical organic functions: alkanes [33,34], alcohols [35][36][37][38][39], alcohol ether [40], acid chlorides [41,42], esters [43,44], aliphatic [45][46][47][48][49][50][51][52][53][54] and aromatic halogens [55,56], aliphatic [57,58], aromatic ketones [59], nitriles [60], and aliphatic [61,62] and aromatic amines [63].…”

Acid-base behavior in aprotic organic solvents

“…Probably B(HA)2 is sometimes formed by direct interaction of B and (HA)2 (eq 68), as postulated by Kaufman and Singleterry when interpreting cryoscopic data for amine-carboxylic acid systems in benzene; a further association of B(HA)2 with (HA)2 was also thought to occur (eq 69) [473]: B+ (HA)2^B(HA)2 (68) B(HA)2+ (HA)2^B(HA)4. (69) On the other hand, when the part of the carboxylic acid is present as monomer, or as monomer loosely bound to solvent molecules, eq 63 may be a preferable formulation: BH^..A-+ H-A^BH+...A-...H-A. While emphasizing homoconjugation in 1:1 ratio as the most frequently observed type, we should not ignore occasional indications of conjugation in other ratiosfor instance, there have been reports of adsorption of carboxylic acids in excessive amounts on ion-exchange resins.…”