In this paper, we report the reactivity of fluoro-N, N, N', N'-tetramethylformamidinium hexafluorophosphate ( TFFH), a reagent for transformation of carboxylic acids into acid fluorides in solution, toward self-assembled monolayers ( SAMs) of 16-mercaptohexadecanoic acid on gold. Contrary to the solution-based reactions, we found that only interchain carboxylic anhydrides ( ICAs), not acid fluorides ( AFs), were obtained at surfaces by the facile interchain reaction under most reaction conditions studied. AFs were found to be formed only when tetrabutylammonium fluoride, a reagent inducing fast decomposition of ICAs, was added to the reaction mixture. The reactivity of TFFH toward carboxylic acid-terminated SAMs was different from that of cyanuric fluoride, which has been reported previously ( Langmuir 2005, 21, 11765-11772). This study provides more insight into the role of the proximity effect in SAM-based reactions as well as another approach to the formation of ICAs from carboxylic acid-terminated SAMs.