Structures of amphiphilic molecules at the liquid/solid and solid/solid interfaces are important in understanding lubrication, colloid stabilization, chromatography, and nucleation. Here, we have used interface-sensitive sum frequency generation (SFG) spectroscopy to characterize the interfacial structures of long-chain alcohols above and below the bulk melting :temperature (T-m). The melting temperature of the ordered hexadecanol monolayer was measured to be around 30 degrees C above the bulk T-m, consistent with the transition temperature reported using X-ray reflectivity [Phys. Rev. Lett 2011, 106, 137801]. The disruption of hydrogen bonds between the sapphire and the alcohol hydroxyl groups was directly measured as a function of temperature. The strength of this hydrogen-bonding interaction, which explained the monolayer thermal stability above T-m, was calculated using the Badger-Bauer equation. Below T-m, the ordered self-assembled monolayer influenced the structure of the interfacial crystalline layer, and the transition from the ordered monolayer to the bulk crystalline phases (alpha rotator phase, beta crystalline phase, and gamma crystalline phase) resulted in packing frustrations at the interface.