The quenching of multibubble sonoluminescence, MBSL, by seven organic monomers in aqueous solution using ultrasound at two frequencies is reported. The results at 515 kHz closely parallel those reported for other simple organic compounds in solution. However, at 20 kHz, significant differences from those at the higher frequency were observed with lower degrees of quenching. In some cases, enhancement of the MBSL was observed. These effects are accounted for in terms of a model where monomer adsorbs to the bubble/solution interface and different types of cavitation can be observed at the two frequencies. The implication of the results for polymerization of these monomers is discussed.