Synthesis of Oxadiazoles and Examination of Steric Effects in a Cyclodehydration Reaction

The objective of this project is to develop a general substrate scope by testing various steric and electronic effects. This is pursued by developing triphenylphosphine dibromide (PPh3Br2) as an effective cyclodehydration reagent for use with a variety of hydrazides and sterically and electronically different benzoic acids. The two phases of the experiment include assessing yield through a cyclodehydration reaction and comparing that yield to the steric hindrance and molecular structure recorded in different databases. The cyclodehydration reaction uses ortho-substituted benzoic acid with store bought PPh3Br2, and compares those yields to the use of a two step-one pot reaction in place of the PPh3Br2. Experimental published data is collected using software ConQuest/Mercury to access Cambridge Crystallographic Data Centre. This data is then then compared to computational data from ChemBio3D Ultra. Because bond length was very similar among the various benzoic acids, it cannot be determined how bond length affects yield. Torsion angle data values differ significantly between the experimental data and the computational data. However, similar trends in data are seen across both methods. In both methods, the 2-Methylbenzoic acid and o-Methoxybenzoic acid show a smaller torsion angle than oBromobenzoic acid and o-Chlorobenzoic acid signifying more steric hindrance in 2-Methylbenzoic acid and o-Methoxybenzoic acid. Comparing this to the yield of these benzoic acids show that the smaller the torsion angle, the less reactive the benzoic acid is. Benzoic acid is an exception to this with a small torsion angle and high yield. Due to the lack of an ortho-substituent, the small torsion angle does not increase steric hindrance and therefore does not negatively affect yield