Graduation Year

2023

Document Type

Honors Thesis

Degree Name

Bachelor of Arts

Department

Biological and Physical Sciences

Faculty Advisor

Benjamin Knurr

Abstract

In early chemistry education, students are often taught to think about electrons as small, negatively charged particles existing in planetary orbits around the nucleus of an atom, rather than creating an electron cloud. In reality, electrons exhibit wave-particle duality, and are best described as wave functions. This idea that the electrons travel as waves and are moving around the nucleus so quickly that it is not possible to know the speed or location of an electron at any given moment is extremely abstract and difficult to visualize. This concept is essential to the theory of quantum mechanics, and therefore is fundamental to undergraduate physical chemistry courses. To assist students in gaining a better understanding of these concepts, this thesis project proposes an undergraduate laboratory experiment, focusing on applying the particle-on-a-ring theory to porphyrins. Several porphyrin molecules with different meso-substitutions were synthesized and analyzed using UV/Vis spectroscopy and the particle-on-a-ring model to calculate experimental carbon-carbon bond lengths. All the calculated bond lengths differed from the literature value by varying degrees. It appears that the difference in values is due primarily to the presence of additional orbitals of appropriate orientation allowing the porphyrin π system to delocalize into them and thus expand the ring. These additional orbitals are likely affected by the presence of an additional π system, the electronegativity of the atoms in the substituent groups, and/or the possibility of hyperconjugation of the substituent molecular orbitals. Synthesizing their own porphyrin molecules for analysis gives students a sense of ownership over their experiment and writing a report on that analysis gives students the opportunity to explore the particle-on-a-ring model on a deeper level. By asking students to explain how the model works and at what point it breaks allows them to gain a better understanding of the particle-on-a-ring system, and therefore, basic quantum mechanics.

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