Constant Trouton

Por most normal liquids the constant has a value of approx. 88JmolK" . Associated liquids show marked variations from this value. The Trouton constant is the molar entropy of vaporization. 

Troubleshooting Trouton constant Troxerutin [7085-55-4] Troysan 174 Troysan 192 True color holograms TrueType Truex process Truncatella sp. Truscottite [12425-42-2] Truxal Trycol... 

After evaporating the solvents and hydrogen halides the free acids can be purified by fractional distillation in vacuo. It was not possible to isolate the acid with X = J (7). The high value of the Trouton constant (25.1 cal/Mol °K) (7) seems to indicate, that H[P02FC1] and H[P02pBr] as well are associated over hydrogen bridges. 

Vapor density measurements (37, 226) and mass spectroscopy (226, 300) were used to show that ClFgO is monomeric in the gas phase. The relatively high boiling point and Trouton constant of ClFgO imply its association in the liquid phase. More specific evidence about the nature of this association was obtained from the vibrational spectra... 

The measured vapor density of CIF3O2 indicates that no appreciable association occurs in the gas phase. Its relatively low boiling point and Trouton constant imply little association in the liquid phase. This prediction is confirmed by the vibrational spectra of the liquid and the neat solid which exhibit only minor frequency shifts when compared to... 

The degree of association of molecules in a liquid can be estimated by means of its Trouton constant (Nash, 1984). At the normal boiling temperature, Tpp, vaporization proceeds with standard molar changes of enthalpy, AH%, and entropy, AS°bp, from which Trouton s rule is derived as given in eqn. 3.10. 

This rule works best for apolar, quasi-spherical molecules. Large deviations occur when chemical association is involved (e.g., carboxylic acids), from molecular dipolarity (e.g., dimethyl sulfoxide), and from molecular asphericity (e.g., neopentane/ -pentane). Strongly associating solvents (e.g., HF, H2, NH3, alcohols, carboxylic acids) have Trouton constants which are higher than the average value of 88 J mol K" found for nonassociating solvents such as diethyl ether and benzene. 

A F. Belyaev, ZhurFizKiiim 22, 91—101(1948) CA 42, 5227(1948) (Boiling points, heats of vaporization and Trouton constants of secondary expls)... 

Fluorine Nitrate, Nitrogen Trioxyfluoride or Nitrosyl Hypofluorite, NOaF, mw 81.01 colorless gas, fr p —175°, bp —45 9°, Trouton Constant 20.81. Either liquid, solid or gas, it explodes readily and violently, and often for no apparent reason... 

It is of some interest to apply Trouton s rule (entropy of vaporization at the boiling point is a constant) to the above data. Unfortunately, boiling points are known only for nitric acid and some of the aliphatic nitrates. Their Trouton constants (AH p/Tbp) are 20.2 and ca 22.8 entropy units, respectively. Thus they straddle the normal Trouton constant of 21 eu. This observation, coupled with the observed constancy of the specific heat of vaporization, suggests that intermolecular bonding in nitrate esters may be relatively weak, or at least consistent... 

According to Ref 10a, Hydrazoic acid molecules are linked into an infinite zigzag chain by N—H... N hydrogen bonds. Thus its high value of specific heat of vaporization is not unexpected. A fairly reliable Trouton constant of 23.5 eu for hydrazoic acid also suggests a non-ideal associated liquid. The other three azides in Table 8 have specific heats of vaporization similar to those of nitrate esters and nitramines... 

The Ramsay-Shields and Trouton constants indicate that arsine is a normal liquid and differs from phosphine and to a greater extent from ammonia in not being associated. 

Occasionally one has available a single vapor pressure point—for example, the normal boiling point—but wishes approximate vapor pressures at other temperatures. Some of the simplest schemes are based on Eq. (2). If the compound is not likely to self-associate through hydrogen bonds or other specific interactions, the Trouton constant (Mfvap/Tboinng) is approximately 21 cal/mol°. Substitution of this value into Eq. (2) shows that the vapor pressure is related to normal boiling point Tb by Eq. (13). 

It should, however, be borne in mind that the theoretical argument can in fact tell us something about the heat of evaporation but not about the boiling point itself, except when the entropy of evaporation (AH/T = Trouton constant, p. 88) shows no differences for related compounds. This is almost correct in the above-mentioned case of cis- and trans-dichloroethylene, namely 21.64 and 21.52 cal/mol. deg., respectively. 

Hengleins represented the vapour pressure curves of two substances by a formula log Ti=a log 3 2+6, where Ti, T2 are the abs. temperatures for equal vapour pressures, and a and b are constants, b being approximately the ratio of the two Trouton constants, where 4 is the latent heat of... 

The liquid has a high Trouton constant and a low dielectric constant. The bond length in the monomer is 1.14 A and the molecule very stable, so that association to N2O2 is endothermic at ordinary temperature. The gaseous molecule has a small dipole moment of 0.16 debye. 

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