The synthesis, structure, and reactivity of undec-10-ene-1-thiol monolayers assembled on planar and nanocrystalline (curved) Au is presented. Cyclic voltammetry and infrared spectroscopy are used to probe the structural changes in the monolayers (on planar Au) upon irradiation with gamma-rays. Oligomerization of the monolayers during the gamma-ray exposures is indicated by the observed decrease in the intensities of infrared bands associated with the olefin functionality. From infrared spectra obtained during gamma-ray exposures of the undec-10-ene-1-thiol monolayers on planar Au, it is proposed that the oligomerization reaction is controlled by the distance the tethered olefin groups can move. That is to say the reaction is stress limited. Dropcast films of undec-10-ene-1-thiol/Au nanoclusters (1.3 and 3.4 nm diameter Au crystals) do not exhibit decreases in the olefin infrared bands after large gamma-ray exposures. This decrease in reactivity for the olefin monolayers supported on the Au nanocrystals is suggested to be the result of interdigitation of the alkane chains from neighboring alkanethiolate Au clusters that exist in the dropcast films.