G4 formation has previously been monitored by noting a frequency shift in the guanine carbonyl stretch frequency. Experimentally, we observe a red shift in the frequency of both guanine carbonyl stretch modes, GCO I (Figure ) and GCO II (Figure ), upon the addition of potassium ions. Peak 80, which is a coupling between GCO I and GCO II, shifts diagonally which supports these assignments. According to the existing literature however, the folding of a single strand to a G4 induces a frequency shift of the guanine carbonyl stretch in the opposite direction. In order to reconcile this discrepancy and in order to understand our experimental observations, we compare calculated EVV 2DIR spectra of the proposed initial structure of a G-quartet (Figure ) and a G4 (Figure ) to experimental spectra of Myc2345 in the absence and presence of potassium ions.