Title
Synthesis and Structural Analysis of Macrocyclic Arenes: Experimental and Computational Insights
Date of Award
Spring 2019
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Chemistry
First Advisor
Timerghazin, Qadir K.
Second Advisor
Reid, Scott A.
Third Advisor
Huang, Jier
Abstract
Synthesis, properties and applications of macrocyclic molecules have been one ofthe interesting branches of organic chemistry during the past century. Several classes ofmacrocyclic molecules, based on their repeating unit and connectivity pattern, have beendiscovered. Macrocyclic arenes, cyclo[n]veratrylenes, calix[n]arenes and pillar[n]arenes,were among the most interesting and studied molecules. The major difference betweenthese molecules is the methylene-bridged connectivity pattern. In the present thesis, Iattempted to synthesize these molecules using novel approach which has been developedin our group and performing some structural analysis using experimental andcomputational techniques.The first synthesized and investigated molecule is the cyclotetraveratrylene(CTTV) which has the ortho (1,2) methylene-bridged connectivity pattern. This moleculeshowed conformational flexibility at the room temperature. This phenomenon intrigued usto investigate its conformational changes upon the one-electron oxidation. The results ofboth experimental and computational studies revealed that the most stable conformer ofthis molecule is different in the neutral (sofa) and cation-radical (boat) states. However,due to instability of the cation-radical structure we have not been able to isolate the crystalstructure of this system.The second synthesized molecules possessing the meta (1,3) methylene-bridgedconnectivity pattern, calix[4]arenes. Herein, I synthesized a series of calix[4]arenes withdifferent substituents to show how the solvent environment and crystal packing forces cantotally change the most stable conformation of these molecules. The results revealed thatin the solution the 1,3-alternate is the most stable conformer, however, in the solid state,the boat is more stable. This phenomenon can be attributed to the intermolecular interactionof calix[4]arenes in the solution with the solvent molecules and in the solid states as theinter-calix[4]arene-calix[4]arene interactions.Pillar[n]arenes are the third class of macrocyclic arenes that were investigated inthis study which have para (1,4) methylene-bridged connectivity pattern. Since the fortuitusdiscovery of pillar[5]arne in 2008, selective synthesis of higher sizes (n > 5) has remainedas an intriguing challenge for organic chemists around the world. Herein, I developed anovel synthetic method which can help us to synthesize pillar[n]arenes (n = 5, 6) selectivelywith high yield. The experimental and computational results indicated that the solvent hassignificant role in the size of the synthesized product. While the dichloromethane cangenerate more pillar[5]arene, using chloroform as the solvent can lead to pillar[6]arene asthe dominant product. This effect can be attributed to the templating effect of the solvent.