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Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 56
Chapter 14, Problem 56

With information from the ¹H NMR and the ¹³C DEPT spectra, structure elucidation becomes even easier. Provide the structure that corresponds to the following data. [The identity of the carbons comes from the DEPT experiment.]
C₆H₁₁BrO₂
IR: 1745 cm ⁻¹
¹H NMR: δ 1.25 (t, 3H), 2.18 (quint, 2H), 2.58 (t, 2H), 3.46 (t, 2H), 4.15 (q, 2H)
¹³C NMR: δ 14.2 (CH₃) , 27.8 (CH₂) , 32.5 (CH₂) , 32.6 (CH₂) , 60.5 (CH₂) , 172.4 (C)

Verified step by step guidance
1
Identify the functional groups: The IR peak at 1745 cm⁻¹ suggests the presence of a carbonyl group, likely an ester or a ketone.
Analyze the ¹H NMR data: The triplet at δ 1.25 (3H) indicates a methyl group adjacent to a methylene group. The quintet at δ 2.18 (2H) suggests a methylene group flanked by two other groups. The triplet at δ 2.58 (2H) and δ 3.46 (2H) suggest methylene groups adjacent to electronegative atoms or groups. The quartet at δ 4.15 (2H) suggests a methylene group adjacent to an oxygen atom, typical for an ester linkage.
Examine the ¹³C NMR data: The chemical shift at δ 172.4 indicates a carbonyl carbon, supporting the presence of an ester. The other chemical shifts correspond to various CH₃ and CH₂ groups, consistent with the ¹H NMR data.
Consider the molecular formula C₆H₁₁BrO₂: The presence of bromine suggests that one of the methylene groups is likely adjacent to a bromine atom. The formula also supports the presence of an ester group, as indicated by the IR and NMR data.
Propose a structure: Based on the data, propose a structure that includes an ester group, a bromine atom, and the appropriate number of carbon and hydrogen atoms. Consider the connectivity suggested by the NMR data, ensuring that the chemical shifts and splitting patterns are consistent with the proposed structure.

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Key Concepts

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

¹H NMR Spectroscopy

¹H NMR spectroscopy is a technique used to determine the structure of organic compounds by analyzing the magnetic environment of hydrogen atoms. The chemical shift (δ) values indicate the type of hydrogen environment, while the splitting pattern (singlet, doublet, triplet, etc.) reveals the number of neighboring hydrogens. In this question, the NMR data provides clues about the connectivity and environment of hydrogen atoms in the molecule.
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¹³C DEPT NMR Spectroscopy

¹³C DEPT (Distortionless Enhancement by Polarization Transfer) NMR spectroscopy is used to differentiate between CH, CH₂, and CH₃ groups in a molecule. It provides information about the carbon skeleton by showing which carbons are bonded to hydrogens. In the given data, DEPT helps identify the types of carbon atoms present, aiding in the construction of the molecular structure.
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Infrared (IR) Spectroscopy

IR spectroscopy identifies functional groups in a molecule by measuring the absorption of infrared light, which causes molecular vibrations. The absorption at 1745 cm⁻¹ suggests the presence of a carbonyl group (C=O), typically found in esters or ketones. This information, combined with NMR data, helps in deducing the functional groups and overall structure of the compound.
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Related Practice
Textbook Question

Assign each signal in the ¹³C NMR spectra to the molecule shown.

(b) <IMAGE>

1
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Textbook Question

How many distinct signals would you expect to see in the ¹H NMR spectrum of the following molecules? [Ignore diastereotopic hydrogens for the sake of this assessment.]

(c)

2
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Textbook Question

Draw the expected results of a DEPT sequence for the molecules shown.

(b)

6
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Textbook Question

How many distinct signals would you expect to see in the ¹H NMR spectrum of the following molecules? [Ignore diastereotopic hydrogens for the sake of this assessment.]

(a)

2
views
Textbook Question

How many distinct signals would you expect to see in the ¹H NMR spectrum of the following molecules? [Ignore diastereotopic hydrogens for the sake of this assessment.]

(b)

2
views
Textbook Question

Draw the expected results of a DEPT sequence for the molecules shown.

(a)