IB Chemistry Topic S3.2.11 H NMR Spectra Interpretation Revision Notes (HL)

IB Chemistry Topic S3.2.11 H NMR Spectra Interpretation Revision Notes (HL) | RevisionDojo

Written by official IB examiners

What Causes Splitting in 'H NMR?

When you observe an 'H NMR spectrum, you’ll notice that some signals are not just single peaks: they are split into clusters of peaks, for example doublets, triplets, and quartets.
This splitting provides crucial information about the number of neighboring hydrogen atoms (protons) near the hydrogen responsible for that signal.
The splitting occurs because of a phenomenon called spin-spin coupling.
Each hydrogen nucleus has a magnetic moment (a tiny magnetic field) due to its nuclear spin.
When hydrogen atoms are close to each other (on neighboring carbon atoms), their magnetic fields interact.
This interaction causes the signal of one hydrogen to split into multiple peaks.

The $n+1$ Rule for Splitting Patterns

The splitting pattern of a signal is determined by the n + 1 rule.
This rule states:
1. The number of peaks in a signal = n + 1, where n is the number of equivalent neighboring hydrogen atoms.

Key Points:

Neighboring hydrogens are those attached to adjacent carbon atoms.
Hydrogens that are chemically equivalent (in the same chemical environment) do not split each other’s signals.
The number of peaks in the splitting pattern corresponds to n + 1.

Tip

When counting neighboring hydrogens, focus on hydrogens attached to carbons directly adjacent to the carbon of the hydrogen being analyzed.
Ignore hydrogens that are further away or part of equivalent groups.

Common Splitting Patterns

Let’s explore the most common splitting patterns and what they tell you:

Singlet

Number of neighboring hydrogens (n): 0

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What Causes Splitting in 'H NMR?

When you observe an 'H NMR spectrum, you’ll notice that some signals are not just single peaks: they are split into clusters of peaks, for example doublets, triplets, and quartets.
This splitting provides crucial information about the number of neighboring hydrogen atoms (protons) near the hydrogen responsible for that signal.
The splitting occurs because of a phenomenon called spin-spin coupling.
Each hydrogen nucleus has a magnetic moment (a tiny magnetic field) due to its nuclear spin.
When hydrogen atoms are close to each other (on neighboring carbon atoms), their magnetic fields interact.
This interaction causes the signal of one hydrogen to split into multiple peaks.

The $n+1$ Rule for Splitting Patterns

The splitting pattern of a signal is determined by the n + 1 rule.
This rule states:
1. The number of peaks in a signal = n + 1, where n is the number of equivalent neighboring hydrogen atoms.

Key Points:

Neighboring hydrogens are those attached to adjacent carbon atoms.
Hydrogens that are chemically equivalent (in the same chemical environment) do not split each other’s signals.
The number of peaks in the splitting pattern corresponds to n + 1.

Tip

When counting neighboring hydrogens, focus on hydrogens attached to carbons directly adjacent to the carbon of the hydrogen being analyzed.
Ignore hydrogens that are further away or part of equivalent groups.

Common Splitting Patterns

Let’s explore the most common splitting patterns and what they tell you:

Singlet

Number of neighboring hydrogens (n): 0

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry S3.2.11 H NMR Spectra Interpretation Notes

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

What Causes Splitting in 'H NMR?

The $n+1$ Rule for Splitting Patterns

Key Points:

Common Splitting Patterns

Singlet

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What Causes Splitting in 'H NMR?

The $n+1$ Rule for Splitting Patterns

Key Points:

Common Splitting Patterns

Singlet

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Duis aute irure dolor in reprehenderit

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