Gas chromatography of all C15C18 linear alkenes on capillary columns with very high resolution power

Retention of long-chain acetylenic hydrocarbons on non-polar stationary phases

The retention indices of methyl and trimethylsilyl esters of octadeca-, eicosa- and tricosa-ynoic fatty acids containing acetylenic bonds were measured on non-polar stationary phase (dimethylsilicone with 5% phenyl groups). An unusually large increase in retention is observed for compounds containing conjugated and methylene interrupted acetylenic bonds. The additional increase in retention index as a result of the presence of one conjugated acetylenic bond is roughly equivalent to the retention increase caused by lengthening of the hydrocarbon chain for one carbon atom. The increase in retention for methylene interrupted bonds constitutes approximately 50% increase for conjugated triple bonds. A further increase in interruption substantially decreases the effect. Based on available literature data and the results of this work, the contributions of conjugated acetylenic and olefinic bonds, and methylene interrupted acetylenic bonds to retention were estimated.

Three-dimensional topographic index applied to the prediction of acyclic C5–C8 alkenes Kováts retention indices on polydimethylsiloxane and squalane columns

A novel approach is described for the prediction of gas chromatographic Kováts retention indices of 150 acyclic C5-C8 alkenes on two stationary phases (polydimethylsiloxane, PDMS, and squalane, SQ). The heuristic method was used to build multiple linear regression models using descriptors calculated by MODLESLAB software and CODESSA program. The resulting quantitative structure-retention relationship (QSRR) models were well-correlated, with predictive R2 values of 0.970 and 0.958 for retention indices on PDMS and SQ columns, respectively. 1Omegap, a three-dimensional (3D) topographic index, was found to play the most important role in the description of the chromatographic retention behavior of the alkenes in these two stationary phases. Moreover, this index could completely distinguish different isomers of alkene. Therefore, it can also be extended to distinguish different isomers of other compounds so that can well describe their quantitative structure-retention relationships.

Data mining for seeking an accurate quantitative relationship between molecular structure and GC retention indices of alkenes by projection pursuit

Primary data mining on alkenes for seeking an accurate quantitative relationship between the molecular structure and retention indices of gas chromatography is developed in this paper. Based on the results obtained from projection pursuit, all alkenes investigated show an interesting classification. Thus, a new variable named class distance variable of alkenes, which essentially describes information about the branch, position of the double bonds, the number of double bonds, and so on for alkenes, is proposed. With the help of the new variable, both fitting and prediction accuracy of the regression model can be dramatically improved. The results obtained in this work show that the technique of projection pursuit developed in statistics is a quite promising tool for seeking an accurate quantitative structure-retention relationship (QSRR).

Semi-empirical topological method for the prediction of the chromatographic retention of cis- and trans-alkene isomers and alkanes

A new index is proposed for the prediction of the chromatographic retention of the cis- and trans-n-alkene isomers and alkanes. This index is based on the hypothesis that the chromatographic retention of the molecule is due to the interaction of each carbon atom with the stationary phase, and consequently the index is reduced by its neighbours' steric effects. The topological values are obtained by a numerical approximation considering the general behaviour of the chromatographic retention of the compounds. The simple linear regressions between the chromatographic retention and the index proposed for all branched alkanes and also isomers of the studied straight-chain C5 and C14 alkenes (1-ene, cis- and trans-2-, 3-, 4-, 5-, 6- and 7-enes) is very good (the correlation coefficient is r = 0.9999), and the elution sequence is correct for most of them. The models have a high predictive ability, as established by cross-validation values (r2cv). Thus, this new method, different from those already existent, can be used as complementary tool for the elucidation of the molecular structure, or prediction of the chromatographic retention of the cis- and trans-alkene isomers and branched alkanes. It could be extended with success, in the future, to the other types of compounds.