Experimental observation of resonance Raman optical activity

We provide the first experimental evidence for resonance Raman optical activity (RROA). In non-aqueous solution (+)-naproxen ((S)-6-methoxy-α-naphthalenacetic acid) and its deuterated methyl ester exhibit monosignate negative RROA, whereas the RROA spectrum of (−)-naproxen sodium is monosignate positive (aqueous solution above pH 10), for 514 nm excitation. In all cases, the RROA bands exhibit the same relative intensities as those in the parent resonance Raman (RR) spectrum, and the ratio of RROA to RR is comparable in magnitude, but opposite in sign, to the electronic circular dichroism (CD) anisotropy ratio of the lowest energy electronic state near 330 nm. These findings are in accord with the theory of RROA in the limit of strong resonance with a single electronic state.