Interfacial chemical transformations are an important way to control the physical and chemical properties of surfaces. Organic molecules that self-assemble into monolayers are a proven, effective tool for surface modification, and the ability to do controlled chemical transformations on the exposed surface of the self-assembled monolayer (SAM) adds significant diversity to this capability. Given the importance of carboxylic acid groups in applications ranging from controlling surface ionization to anchoring biological molecules, we have studied alternative ways to install acid groups on a surface and have probed the factors that control their chemistry. The work reported herein describes a new way to install carboxylic acid groups on surfaces and explores the intermolecular chemistry between acid groups on adjacent monolayer-forming molecules both on flat interfaces and on nanoparticles. It addresses the interplay of molecular flexibility and chain packing in controlling processes that bridge neighboring molecules. Finally, the creation of bridged diacyl peroxides from neighboring acid groups provides useful surface bound polymerization initiators that can effectively and conformally cover both flat surfaces and particles with ultrathin polymer films.