Programmable control of electron transport through organic molecules is a crucial step for designing integrated electronic devices for energy storage. Recent advances in molecular electronics have brought us closer towards achieving the ultimate limits in miniaturization and spatial and functional control over electronic performance. Despite recent progress, however, we still lack a full understanding of molecular-scale electron transport and how these properties are affected by chemical identity and sequence. In this work, we directly measure single molecule conductance using a scanning tunneling microscope-break junction (STM-BJ) technique. Oxazole-terminated molecules are found to exhibit interesting quantum interference phenomena through central phenyl rings and terminal oxazole rings, which can be used for controlling charge transport. In particular, the quantum interference of the central phenyl group follows a quantum circuit rule such that Gpara/Gmeta = 6, whereas the c-type terminal oxazole ring shows constructive quantum interference. We can further precisely tune the conductance of oligophenyls via aromatic interaction with different background molecules. In this way, our work provides the fundamental electron and charge transport information to inform future programmable molecular electronics design.