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Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
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All textbooksMullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 61e
Chapter 14, Problem 61e

Draw the signal for the following multiplicities. What is the ratio of peaks within each signal?
(e) sextet

Verified step by step guidance
1
Understand the concept of multiplicity in NMR spectroscopy: Multiplicity refers to the splitting pattern of a signal in an NMR spectrum, which is determined by the number of neighboring hydrogen atoms (n) according to the n+1 rule.
Identify the number of neighboring hydrogens: For a sextet, the multiplicity indicates that there are 5 neighboring hydrogens (n = 5), since a sextet is n+1 = 6.
Determine the ratio of peaks: The ratio of peaks in a multiplet is determined by Pascal's triangle. For a sextet, the ratio of peaks is 1:5:10:10:5:1.
Draw the signal: A sextet will have six peaks with the intensity ratio of 1:5:10:10:5:1. This means the outermost peaks are the smallest, and the middle peaks are the largest.
Visualize the signal: When drawing the sextet, ensure that the spacing between the peaks is consistent, and the height of each peak corresponds to the ratio determined in the previous step.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

NMR Multiplicity

NMR multiplicity refers to the splitting of NMR signals into multiple peaks due to spin-spin coupling between non-equivalent hydrogen atoms. The number of peaks in a signal is determined by the n+1 rule, where n is the number of neighboring hydrogen atoms. Understanding multiplicity is crucial for interpreting NMR spectra and identifying molecular structures.
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Sextet in NMR

A sextet in NMR spectroscopy is a signal split into six peaks. This occurs when a hydrogen atom is coupled with five equivalent neighboring hydrogen atoms (n=5), resulting in a 6-peak pattern. The intensity ratio of these peaks typically follows Pascal's triangle, specifically 1:5:10:10:5:1 for a sextet, reflecting the statistical distribution of spin states.
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Pascal's Triangle in NMR

Pascal's Triangle is used in NMR to predict the relative intensities of peaks in a multiplet. Each row of the triangle corresponds to the coefficients of the binomial expansion, which represent the intensity ratios of the peaks. For example, a sextet's intensity ratio is derived from the sixth row, providing a clear pattern for interpreting complex splitting in NMR spectra.
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Related Practice
Textbook Question

For the hydrogen(s) screened in blue, draw the signal you would expect to see in a ¹H NMR spectrum. At which chemical shift would the signal appear?

(c)

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Textbook Question

Draw the signal for the following multiplicities. What is the ratio of peaks within each signal?

(d) quintet

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Textbook Question

Draw the signal for the following multiplicities. What is the ratio of peaks within each signal?

(c) quartet

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Textbook Question

Draw the signal for the following multiplicities. What is the ratio of peaks within each signal?

(b) triplet

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Textbook Question

Draw the signal for the following multiplicities. What is the ratio of peaks within each signal?

(f) septet

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Textbook Question

For the hydrogen(s) screened in blue, draw the signal you would expect to see in a ¹H NMR spectrum. At which chemical shift would the signal appear?

(e)

952
views