Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

15. Analytical Techniques:IR, NMR, Mass Spect

H NMR Table

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

H NMR Table

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3:24 minutes

Problem 14c

Textbook Question

Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.
c. ClCH₂CH₂CH₂Cl

Verified step by step guidance

Step 1: Analyze the structure of the molecule provided. The molecule contains three carbon atoms, each bonded to hydrogen atoms and bromine atoms. The bromine atoms are electronegative and will influence the chemical shift of nearby protons in NMR spectroscopy.

Step 2: Identify the protons in the molecule. There are three sets of protons: (1) the protons on the CH2 group directly bonded to the bromine atom on the left, (2) the protons on the middle CH2 group, and (3) the protons on the CH2 group bonded to the bromine atom on the right.

Step 3: Consider the electronegativity of bromine and its effect on the chemical shift. Bromine is highly electronegative and deshields nearby protons, causing them to resonate at higher frequencies in NMR spectroscopy. Protons farther from bromine will experience less deshielding and resonate at lower frequencies.

Step 4: Rank the protons based on their proximity to bromine atoms. The protons on the CH2 group directly bonded to bromine will resonate at the highest frequency due to the strong deshielding effect. The protons on the middle CH2 group, which are equidistant from both bromine atoms, will resonate at a lower frequency. The protons on the CH2 group bonded to the bromine atom on the right will resonate at the next highest frequency.

Step 5: Assign labels to the protons based on their chemical shift. The protons on the middle CH2 group will give the signal at the lowest frequency and are labeled 'a'. The protons on the CH2 group bonded to the bromine atom on the left will give the signal at the next lowest frequency and are labeled 'b'. The protons on the CH2 group bonded to the bromine atom on the right will give the signal at the highest frequency and are labeled 'c'.

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Key Concepts

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

Chemical Shift in NMR Spectroscopy

In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift refers to the resonance frequency of a nucleus relative to a standard in a magnetic field. It is influenced by the electronic environment surrounding the nucleus, with protons in electron-rich environments appearing at higher frequencies (downfield) and those in electron-poor environments appearing at lower frequencies (upfield). Understanding chemical shifts is crucial for interpreting NMR spectra and identifying different types of protons in a compound.

Electronegativity and Inductive Effect

Electronegativity is the tendency of an atom to attract electrons towards itself. In organic compounds, electronegative atoms like bromine can exert an inductive effect, pulling electron density away from nearby protons. This effect can deshield the protons, causing them to resonate at lower frequencies in NMR spectroscopy. Recognizing the influence of electronegative substituents is essential for predicting the order of proton signals in an NMR spectrum.

Proton Environment and Signal Splitting

The environment of protons in a molecule affects their NMR signals. Protons that are in similar environments will resonate at the same frequency, while those in different environments will produce distinct signals. Additionally, the splitting of signals due to neighboring protons (n+1 rule) provides information about the number of adjacent protons. Understanding these concepts helps in accurately labeling and interpreting the signals in an NMR spectrum.

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Related Practice

Textbook Question

Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.

Textbook Question

Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.

Textbook Question

Label each set of chemically equivalent protons, using a for the set that will be at the lowest frequency in the ¹H NMR spectrum, b for the next lowest, and so on. Indicate the multiplicity of each signal.

Textbook Question

Explain the relative chemical shifts of the benzene ring protons in Figure 14.18.

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Textbook Question

Explain why the chemical shift of the OH proton of a carboxylic acid is at a higher frequency than the chemical shift of an OH proton of an alcohol.

Textbook Question

Which underlined proton (or sets of protons) has the greater chemical shift (that is, the higher frequency signal)?

Textbook Question

Which underlined proton (or sets of protons) has the greater chemical shift (that is, the higher frequency signal)?

Textbook Question

The methyl hydrogens in propane appear at a chemical shift of 0.9 ppm, whereas the methyl hydrogens of propene appear around 2.5 ppm. Explain.

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Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.c. ClCH2CH2CH2Cl

Key Concepts

Chemical Shift in NMR Spectroscopy

Electronegativity and Inductive Effect

Proton Environment and Signal Splitting

Watch next

Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.
c. ClCH₂CH₂CH₂Cl