In this study, the conformational preferences and large amplitude motions (LAM) of a series of methoxypyridines (MOPY), as well as 2-methoxyfuran (2-MOF) and 2-methoxythiophene (2-MOTH) are investigated computationally, using DFT methods. Additionally, 2-MOF and 2-MOTH were studied experimentally using chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy in the 75 - 100 GHz region. In analogy with the previously investigated 2-MOPY, 3-MOPY shows conformational preference due to electronic and steric interactions between the methoxy group and pyridine ring. Additionally, a resonance based argument is provided for understanding the barriers to internal rotation for the three MOPY isomers. Rotational spectroscopy of 2-MOF and 2-MOTH are used to experimentally characterize the molecular geometry and LAM that was investigated computationally. Observed rotational constants and barriers to internal rotation were found to be in close agreement with the experimental spectra. In future experiments, we will examine the high temperature decomposition of these heterocycles into synthetically and environmentally important radicals.