Determining The Polarity Of 2-Decomplete Molecules

In this experiment, we computationally predicted the dipole moments of 5 different analyte molecules using the program Spartan. We constructed the molecules online as the program then calculated their dipole moments (polarity). We then experimentally determined the 5 analyte molecules retention factors using the TLC method in the lab. Polarity in organic chemistry refers to a separation of electric charge leading to a molecule having an electric dipole moment1. To determine whether a molecule is polar or nonpolar depends on a molecules structure. This is done by comparing the electronegativity’s of each element in the molecule that are bonded to each other. If a molecules dipole moment eliminates each other due to its symmetrical shape, it is considered to be

nonpolar.

Vice versa, if a molecules dipole moment doesn’t cancel out, due to its asymmetrical structure, it is then considered to be a polar molecule. It is predicted that the higher the Rf value, the lower the dipole moment of a molecule and vice versa2. This is experimentally proven correct, except for the one compound, 2-Decanol. The polarity of 2-Decanol was known to be 1.52 D based off of the Spartan program. Compared to the other analyte compounds it was shown that 2-Decanol was the fourth highest in its dipole moment value, therefore it was expected to have the fourth lowest retention factor value. However, in our calculations, 2-Decanol has the lowest retention factor value. Ignoring the ambiguity of 2-Decanol, it was proven that the compound 1-Decene had the lowest polarity, and the highest Rf value. Butyl Butyrate had the second lowest polarity, and the second highest Rf value. 2-Decanone has the second highest polarity, and the second lowest Rf value. And lastly, Decanoic Acid has the highest polarity, and the lowest Rf value, again dismissing

2-Decanol.

Chromatography is used to separate different molecules for their identification3. It is usually composed of the stationary and mobile phase. The mobile phase is what carries the molecule sample along the solvent used in the lab, and the stationary phase is the interaction between the solvent and the molecules intermolecular forces. When the molecules are dragged up the along the plate by the mobile phase, circular shapes begin to form indicating the measurement of the molecules; how far they traveled along the plate. The stronger the interaction, the slower the movement of the compounds. The analyte compound 1-Decene has London Dispersion Forces as its dominant intermolecular interaction. The compounds 2-Decanone, and Butyl Butyrate have Dipole – Dipole Forces as their dominant intermolecular forces, and the compounds Decanoic Acid, and 2-Decanol have Hydrogen Bonding Forces as their dominant intermolecular forces. Therefore, the analyte compounds Decanoic Acid and 2-Decanol were the slowest of all the compounds used. This is shown between the two compounds that we were assigned, Butyl Butyrate and 2-Decanol. As they traveled up the plate, it was shown that 2-Decanol traveled a shorter distance. This is due to Butyl Butyrate having a weaker intermolecular interaction force, therefore traveling faster.

Any possible errors were not building the compounds correctly on the program Spartan, resulting in incorrect dipole moment calculations. Also not placing enough solution of the compounds on the plates, affecting the results of Rf values. Another possible error in the lab could have been measuring the distance of the spots incorrectly.