Identification of an Unknown Compound by Combined Use of IR, 1H NMR, 13C NMR, and Mass Spectrometry: A Real-Life Experience in Structure Determination

Abstract

In this introductory organic chemistry experiment, the students get an opportunity to analyze and identify an unknown compound as it is done in a real-laboratory setting. First, students are instructed on the proper operation of three major instruments, NMR, IR, and GC–MS, and are given a sample of an unknown compound. The students are expected to operate these three instruments on their own so as to obtain 1H NMR, 13C NMR, IR, and MS spectra of their unknown sample. They must then interpret the data from each of the four spectroscopic methods simultaneously to elucidate the chemical structure of the unknown compound. In this exercise, the instructor does not provide a list of possible unknowns so as to narrow the search for the students. All the knowledge about the nature of the compound is obtained from the spectral data.

Metabolite Profiling of Manilkara zapota L. Leaves by High-Resolution Mass Spectrometry Coupled with ESI and APCI and In Vitro Antioxidant Activity, α-Glucosidase, and Elastase Inhibition Assays

“…Determination of precise mass and its fragmentation peak using tandem mass spectrometry (MS/MS) aids in the elemental composition information for unknown compound identification. However, for accurate and isomeric identification, we needed to follow a sequential analysis using liquid chromatography mass spectrometry (LC MS), infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy [ 40 , 41 ].…”

Learning H-Coupled 13C NMR in the First Month of Sophomore Organic Lecture

“…While there has been much discussion [13][14][15][16][17][18][19][20][21][22][23][24][25][26] of the use of 13 C NMR in the sophomore organic course -Chamberlain 23 in particular nicely summarized the reasons to teach 13 C NMR before 1 H NMR -this has mostly focused on the laboratory portion of the course, or on advanced [27][28][29][30][31][32][33][34][35] coursework. Instruction in elementary 13 C NMR from the beginning of the lecture course can equip the student with the tools necessary to solve simple structural problems.…”

Molecular networking as a dereplication strategy for monitoring metabolites of natural product treated cancer cells

“…Conventionally, spectra of a natural product obtained by liquid chromatography–mass spectrometry, nuclear magnetic resonance and infrared spectroscopy are interpreted based on prior knowledge, or at least “postulation” to the chemical structures of the analyte compounds . Recently, a dereplication strategy utilizing Global Natural Product Social (GNPS) molecular networking has been proposed to leverage the structural features of known compounds to decrypt the tandem mass spectra of unknown compounds .…”

“…Conventionally, spectra of a natural product obtained by liquid chromatography-mass spectrometry, 9,10 nuclear magnetic resonance 11 and infrared spectroscopy 12 are interpreted based on prior knowledge, or at least "postulation" to the chemical structures of the analyte compounds. 13 Recently, a dereplication strategy utilizing Global Natural Product Social (GNPS) molecular networking has been proposed to leverage the structural features of known compounds to decrypt the tandem mass spectra of unknown compounds. [14][15][16][17] Specifically, cosine similarities among each pair of tandem mass spectra of individual specialized metabolites are calculated, of which the compounds with similar chemical structures are prone to cluster together.…”