The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Enhancement of the chiroptical response of α-amino acids via N-substitution for molecular structure determination using vibrational circular dichroism》. Authors are Polavarapu, Prasad L.; Santoro, Ernesto; Covington, Cody L.; Raghavan, Vijay.The article about the compound:H-Trp-OMe.HClcas:7524-52-9,SMILESS:N[C@@H](CC1=CNC2=CC=CC=C12)C(OC)=O.[H]Cl).Formula: C12H15ClN2O2. Through the article, more information about this compound (cas:7524-52-9) is conveyed.
The chiroptical response in the form of vibrational CD (VCD) in the midinfrared region is found to be enhanced when a hydrogen of amino group of L-tryptophan is substituted with acetyl, acryloyl, or maleyl group. The order of preference for VCD enhancement is found to be acryloyl > acetyl > maleyl group. The resulting exptl. VCD spectra are also found to be satisfactorily reproduced by the quantum mech. (QM) predicted spectra. The QM predicted spectra were simulated using the conformer populations, (a) predicted by Gibbs energies and (b) optimized to maximize the similarity between exptl. and predicted VCD spectra. It is found that the conformer populations predicted by Gibbs energies do not yield the maximum possible similarity between exptl. and the QM predicted spectra. This work identifies the N-substitution of α-amino acids and determining the conformer populations that best reproduce the exptl. spectra as two new approaches for mol. structure determination
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Reference:
1,3-Benzodioxole – Wikipedia,
Dioxole | C3H4O2 – PubChem