Chapter 20: Mass Spectrometry and Structure Determination

Solving Molecular Puzzles

Mass spectrometry provides information about molecular mass and fragmentation patterns.

Combined with infrared and NMR spectroscopy, mass spectrometry allows chemists to determine molecular structures.

The process resembles solving a puzzle in which multiple pieces of evidence must be integrated.

Mass spectrometry provides clues regarding:

These features help narrow structural possibilities.

Experienced chemists rarely rely upon a single technique.

Instead, they integrate:

Functional groups.

Hydrogen environments.

Carbon environments.

Molecular mass and fragmentation.

Together, these methods provide a remarkably powerful framework for determining molecular structure.

Beginning students often view spectroscopy as a collection of unrelated techniques.

Experienced chemists treat spectroscopy as a process of assembling evidence.

The goal is not memorization but interpretation.

Throughout spectroscopy, familiar ideas continue to appear:

Organic chemistry repeatedly revisits the same principles from new perspectives.

Better approach: Combine evidence.

Better approach: Approach structure determination as a puzzle.

I can:

☐ Explain what mass spectrometry reveals about a molecule.

☐ Recognize the role of fragmentation in structure determination.

☐ Combine IR, NMR, and MS evidence into a single structural proposal.

Spectroscopy reveals what molecules are.

The final part of the handbook explores how chemists decide what molecules should become.

This shift from analysis to design introduces retrosynthesis, strategy, and the art of molecular construction.

Common fragment losses and diagnostic ions are collected in Appendix D.