Introduction

Study on associative properties of aliphatic alcohols¹, aliphatic carboxylic acids², phenols³, and aliphatic amines⁴ based on their surface tension data, EÖTVÖS constants (k), order of association (x) and Trouton’s rule is a major breakthrough from our laboratory hither to not reported earlier in literature. In the present study, various compounds like hydrocarbons, and compounds having different functional groups with different hetero atoms were taken to see the effect of these groups on surface tension, EÖTVÖS constants (k), order of association (x) and Trouton’s rule.

Experimental and data source

All the surface tension data used in this article is from reference.² The detailed procedure for calculation of various parameters mentioned in table 1 are described in references 1-4. Thermo chemical data is from reference.⁶ Taft s^* values are from reference.⁷ Linear correlation was done using the KaleidaGraph software, Reading, PA, USA.

Discussion

In continuation of our earlier work.¹, the present study is to search for the associative and non-associative behavior of hydrocarbons, ethers and organic compounds having different functional groups with hetero atoms based on surface tension, EÖTVÖS constants (k), order of association (x) and Trouton’s Rule. As a first observation, figure 1 shows the correlation of surface tensions with Taft s^* (R = 0.9531).

Figure 1   Click here to view figure

It is interesting to note that there is a clear discrimination between hydrocarbons, ethers and other organic molecules having different functional groups with hetero atoms toward surface tension. At first sight we thought that hydrocarbons (sl. no. 1, 2, 3, 5, 9) and ethers (sl. no. 14, 15) may correlate well with Taft s^* values because their Ramsey-Shields-EÖTVÖS constants (k) are close to 2.12 or little higher [8], and order of association (x) is less than 1. The molecules with Ramsey-Shields-EÖTVÖS constants (k) are close to 2.12 or little higher⁸, and order of association (x) is less than 1 are supposed to be normal molecules and they contain identical molecules in the vapor and liquid states, hence they are believed to obey the Taft equation. But to our surprise they did not obey the Taft correlation and fortunately they even did not fall under the category of the other molecules having functional groups with hetero atoms. These molecules did not even obey the Troutons rule [9] (see table 1 for their DS_V values). They belong to their own category without any Taft correlation. On the other hand the molecules (sl. no. 10, 11, 12, 13, 16, 19, and 20) which are not supposed to follow the Taft correlation did follow the Taft correlation. The reasons for this inference is that the molecules with functional groups containing hetero atoms and with Ramsey-Shields-EÖTVÖS constants (k) are less than 2.12 and order of association (x) is more than 1 are supposed to be associated. If the molecules are associated the Taft s^* values have no meaning hence no Taft correlation should have been observed. But to our surprise the molecules having functional groups with hetero atoms correlated well (r = 0.9531). These are the molecules (with sl. no. 10, 11, 12, 13, 15, 16, 17 this is a solid, 19, and 20) which are liquids at 20^oC belong to one category and have their own path of Taft correlation. Also they obeyed Trouton’s rule⁹ (see table 1 for their DS_V values). However there is an exception with methanol and acetic acid (sl. no 10 and 13) which did not follow Trouton’s rule⁹ and their order of association is more than one. And the molecules with very low boiling points and ethers belong to other category. Note that the explanation given above cannot explain why some molecules like 4, 6 and 7 which are hydrocarbons did correlate in Taft equation along with associative molecules.

As a conclusion it could be understood that there is a clear distinction between hydrocarbons, ethers and organic compounds having different functional groups with hetero atoms toward surface tension, Ramsey-Shields-EÖTVÖS constants (k), order of association (x) and Trouton’s rule. The hydrogen acceptor (H_a) and donor (H_d) site values did have a significant influence on the order of association in the case of methanol, acetic acid acetamide and methyl amine (sl. no. 10, 13, 17 and 18).

Table 1: Data of Surface tension (g) computed to 0oC (reference 5), Eötvös constants (k), order of association (x), density and other thermodynamic quantities of organic compounds with different functional groups   Click here to view table

References

1. R. Sanjeev, V. Jagannadham and Adam A. Skelton, World Journal of Chemical Education. 2014;2:39
2. R. Sanjeev, V. Jagannadham, Adam A. Skelton, Journal of Molecular Liquids. 2016;224:43–46
3. R. Sanjeev, V. Jagannadham, Adam A. Skelton and R. Veda Vrath, Asian Journal of Chemistry. 2015;27:10:3297
4. R. Sanjeev, V. Jagannadham, Adam A Skelton and R. Veda Vrath, Research Journal of Chemistry & Environment. 2015;19:2:24-30
5. Joseph J. Jasper, J. Phys. Chem. Ref. Data. 1972;1:841.
6. Majer, V.; Svoboda, V., Enthalpies of Vaporization of Organic Compounds: A Critical Review and Data Compilation, Blackwell Scientific Publications, Oxford, 1985, 300. Url: http://old.iupac.org/publications/books/author/majer.html, and link for the data: https://www.google.co.in/?gfe_rd=ctrl&ei=5DT_Upa1A6TM8geCkoBw& gws_rd=cr#q=enthalpy+of+vaporization+and+fusion+pdf
7. Taft s^* values are from Lange’s Hand Book of Chemistry, Ed by John A. Dean, 15^th Edition, McGRAW-Hill, INC, New York, Copy Right Ó 1999.
8. Eötvös, Ann. der Physik., 27, 448 (1886): Cited in: Palit, Santi R. (1956). "Thermodynamic Interpretation of the Eötvös Constant", Nature 177 (4521): 1180 1180.Bibcode:1956 Natur.177.1180P. doi:10.1038/1771180a0
9. Trouton, F. (1884). "IV. On molecular latent heat", Philosophical Magazine Series 5 18 (110): 54–57.doi:10.1080/14786448408627563, and Atkins, Peter (1978). Physical Chemistry, Oxford University Press ISBN 0-7167-3539-3