Isotopomer and InChI Student Worksheet

The following worksheet and key is designed for organic chemistry students and can download and modified as needed.

Learning Objectives:

• Isotopomers and isotopologues are analogous molecules that differ by isotope composition and/or position within a molecule. Isotopomers have known isotopic position, while isotopologues have unknown isotopic position with a molecule.
• Determine which analytical tools can be used to identify isotopologues and isotopomers.
• The International Chemical Identifier (InChI) can be used to store isotopomer information for retrieval in a chemical database.
• A nonstandard InChI layer can be used when the isotopic positions are unknown.

Success Criteria:

• Given a molecule, draw an isotopomer and an isotopolog
• Explain how mass spectral data can identify isotopologues, but NMR is typically necessary to identify isotopomers.
• Use the InChI isotopic /i layer to identify specific isotopomers and the nonstandard /a layer for the identification of isotopologues.

Prerequisite Knowledge:

• From General Chemistry: An isotope is a variant of a chemical element that has the same number of protons but a different number of neutrons in its nucleus, resulting in different atomic masses.
• From organic chemistry: Constitutional isomers, also known as structural isomers, are compounds with the same molecular formula but different connectivity, or atomic organization.
• From organic chemistry: Mass spectrometry is an analytical technique used to measure the mass-to-charge ratio of ions. It is widely employed to identify the composition of a sample by generating a mass spectrum, which displays the masses of the various components within the sample. The process involves ionizing chemical compounds to generate charged molecules or molecule fragments, which are then separated based on their mass-to-charge ratios.
• From organic chemistry: Nuclear Magnetic Resonance (NMR) spectroscopy is an analytical technique used to determine the structure, dynamics, reaction state, and chemical environment of molecules. It relies on the magnetic resonance properties of certain atomic nuclei. When placed in a strong magnetic field, nuclei of certain isotopes (such as ¹H, ¹³C, and ³¹P) resonate at characteristic frequencies when exposed to radiofrequency radiation. This resonance is influenced by the local chemical environment, making NMR spectroscopy a powerful tool for elucidating molecular structure.