---
title: "Structure Elucidation from a Complete Data Set"
description: "In practice a structure is settled by several techniques at once, not one. Working from a molecular formula, an infrared spectrum and a full set of nuclear magnetic resonance experiments, each piece o"
canonical: https://lightmysky.com/learn/science/structure-elucidation-from-a-complete-data-set-mt_O2uungksMZ
source: https://lightmysky.com/learn/science/structure-elucidation-from-a-complete-data-set-mt_O2uungksMZ.md
retrieved: 2026-09-12
---

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# Structure Elucidation from a Complete Data Set

In practice a structure is settled by several techniques at once, not one. Working from a molecular formula, an infrared spectrum and a full set of nuclear magnetic resonance experiments, each piece of evidence removes candidates until one structure survives.

Subject: Science · Area: Chemistry · Ages 22 to 23
Page: https://lightmysky.com/learn/science/structure-elucidation-from-a-complete-data-set-mt_O2uungksMZ

## Ready when they can

- Derives degrees of unsaturation from an accurate mass formula and states what they permit
- Orders the available experiments so that the cheapest evidence is used first
- Builds fragments from correlation data and connects them into a single candidate
- States which experiment would settle a remaining ambiguity and why

## Lesson: Many spectra, one structure

Light is one wave in many sizes, and each size talks to a different part of a molecule. Infrared light carries the energy of bond vibrations, so an infrared trace names functional groups: O-H and C=O each absorb at its own frequencies. Radio waves are far weaker, and they flip nuclear spins, so NMR reports the surroundings of each atom instead.

Start from the molecular formula, which accurate mass and its isotope pattern deliver. From the formula, work out the degrees of unsaturation: count the carbons, add one, subtract half the hydrogens (counting halogens as hydrogens), and add half the nitrogens. Each degree is one ring or one pi bond, so the number permits only structures that spend exactly that budget.

**Example.** Spend the cheap evidence first: formula, then infrared, then the full NMR set. Build fragments from the correlation maps, where each cross peak ties two atoms together, and join the fragments into a single candidate. Then name the datum that kills the nearest rival, such as one correlation the rival cannot explain.

**Tip.** One spectrum rarely closes the case, because each region sees only its own feature. When two candidates survive, state which experiment would split them and why, and run that one next.

**Recap.** The formula sets the budget, spectra spend it from cheap to dear, and one survivor with its rival ruled out is the answer.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Accurate Mass and Isotope Patterns as Formula Evidence](https://lightmysky.com/learn/science/accurate-mass-and-isotope-patterns-as-formula-evidence-mt_68vjdAPNrc)
- [Two-Dimensional NMR and Assigning a Whole Structure](https://lightmysky.com/learn/science/two-dimensional-nmr-and-assigning-a-whole-structure-mt_UEC4dilKT9)

## Opens up

- [NMR After Assignment: Relaxation, Distance and Exchange](https://lightmysky.com/learn/science/nmr-after-assignment-relaxation-distance-and-exchange-mt_dCV2EbNlF2)