Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 13: Problem 8

Explain how to distinguish between the members of each pair of constitutional isomers based on the number of signals in the proton-decoupled \({ }^{13} \mathrm{C}-\mathrm{NMR}\) spectrum of each member.

Short Answer

Expert verified
Question: Explain how to distinguish between constitutional isomers using the number of signals in the ${ }^{13}\mathrm{C}-\mathrm{NMR}$ spectrum. Answer: To distinguish between constitutional isomers using the number of signals in the ${ }^{13}\mathrm{C}-\mathrm{NMR}$ spectrum, follow these steps: 1. Understand that constitutional isomers have the same molecular formula but different arrangements of atoms. 2. Know that each unique carbon atom in a molecule will produce a signal in the ${ }^{13}\mathrm{C}-\mathrm{NMR}$ spectrum. 3. Identify the number of unique carbon atoms within each isomer by analyzing their structures. 4. Compare the number of signals for each isomer in their ${ }^{13}\mathrm{C}-\mathrm{NMR}$ spectra to identify differences in unique carbon environments. 5. Distinguish between the isomers based on the difference in the number of signals in their ${ }^{13}\mathrm{C}-\mathrm{NMR}$ spectra, with a higher number of signals representing more unique carbon environments, and vice versa.

Step by step solution

01

Understand constitutional isomers

Constitutional isomers are compounds with the same molecular formula but different arrangements of atoms or connectivity. These different arrangements can lead to variations in the number of unique carbon atoms present in each isomer. This, in turn, affects the number of signals in the \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectrum.
02

Understanding the \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectrum

In the \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectrum, each unique carbon atom in a molecule will give a signal. The number of signals in the spectrum corresponds to the number of different carbon environments in the molecule. By comparing the number of signals in the \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectrum of each isomer, we can distinguish between them.
03

Identify the number of unique carbon atoms in each isomer

Analyze the structure of each constitutional isomer and identify the unique carbon environments. A unique carbon environment means that the carbon atom is bonded to different types or numbers of atoms compared to other carbon atoms in the molecule.
04

Compare the number of signals in the \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectrum

For each constitutional isomer, count the number of unique carbon environments and compare them. A different number of unique carbon environments in the isomers will result in a different number of signals in their \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectra. By comparing the number of signals, we can determine which isomer corresponds to which \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectrum.
05

Distinguish between the constitutional isomers

Based on the difference in the number of signals in their \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectra, we can distinguish between the constitutional isomers. The isomer with more unique carbon environments will have more signals in its \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectrum, while the isomer with fewer unique carbon environments will have fewer signals. Following these steps, we can effectively distinguish between different constitutional isomers using the number of signals in their \({ }^{13}\mathrm{C}-\mathrm{NMR}\) spectra.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding 13C-NMR Spectroscopy
When it comes to understanding the intricate details of molecular structure, 13C-NMR spectroscopy stands out as a powerful analytical technique. In essence, this form of nuclear magnetic resonance (NMR) spectroscopy focuses on detecting the carbon-13 isotope, which, despite being less abundant than carbon-12, is vital for providing insights into the arrangement of carbon atoms within organic compounds.

The technique revolves around the response of carbon-13 nuclei to an external magnetic field and the subsequent emission of electromagnetic radiation at a characteristic frequency. This response varies based on the electronic environment surrounding each carbon atom, making it possible to identify different types of carbon atoms within a molecule.

Importantly, the number of distinct signals received in the 13C-NMR spectrum directly corresponds to the number of unique carbon environments in a compound. This relationship between signal and structure is pivotal in identifying not just different types of carbon but also in distinguishing between constitutional isomers.
Identifying Unique Carbon Environments
Within the context of 13C-NMR spectroscopy, the concept of unique carbon environments is central to accurately interpreting spectra. A unique carbon environment refers to a carbon atom whose chemical surroundings differ from those of any other carbon atoms in the structure. This uniqueness could stem from varying factors such as the number and type of attached atoms or the electron distribution due to differing functional groups.

For instance, a carbon atom bonded to four different groups represents a unique environment distinct from another carbon bonded to three hydrogens and one carbon. In practice, identifying these environments requires carefully examining the molecular structure to discern how each carbon differs from the others. The upshot of this analysis is that each unique carbon will yield a separate peak in the 13C-NMR spectrum, thereby serving as a fingerprint for the molecule's carbon framework.
Deciphering Molecular Structure Analysis
The final step, molecular structure analysis, marries the theoretical knowledge obtained from the 13C-NMR spectroscopy with practical application. This phase involves comparing the spectra of constitutional isomers – molecules with the same number of atoms but different bonding arrangements – to identify which is which.

To do this effectively, one must scrutinize each molecule's framework to pinpoint unique carbon atoms. Differences in bonding or the presence of various groups result in distinct signals in the 13C-NMR spectrum. The number of these signals reflects the count of unique carbon environments, varying between isomers.

Using these findings, we can conclusively differentiate constitutional isomers, associating each distinct spectrum with a corresponding structure. The examination of minute structural nuances, such as the position of a functional group or the branching of carbon chains, is pivotal in this process, rendering 13C-NMR spectroscopy an indispensable tool for chemists in both the academic and industrial realms.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

\({ }^{13} \mathbf{C}-\mathrm{NMR}\) is like \({ }^{1} \mathrm{H}-\mathrm{NMR}\), except the nuclear spins of \({ }^{13} \mathrm{C}\) nuclei are being analyzed. \- \({ }^{13}\) C-NMR spectra are commonly recorded in a hydrogen-decoupled instrumental mode. In this mode, all \({ }^{13} \mathrm{C}\) signals appear as singlets. \- The number of different signals in a \({ }^{13} \mathrm{C}-\mathrm{NMR}\) spectrum tell you how many nonequivalent carbon atoms are in a molecule. \- \({ }^{13}\) CNMR chemical shifts tell you what kind of carbon atoms are present.

Compound M, molecular formula \(\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}\), readily decolorizes \(\mathrm{Br}_{2}\) in \(\mathrm{CCl}_{4}\) and is converted by \(\mathrm{H}_{2} / \mathrm{Ni}\) into compound \(\mathrm{N}\), molecular formula \(\mathrm{C}_{3} \mathrm{H}_{12} \mathrm{O}\). Following is the \({ }^{1} \mathrm{H}-\mathrm{NMR}\) spectrum of compound \(\mathrm{M}\). The \({ }^{19} \mathrm{C}-\mathrm{NMR}\) spectrum of compound \(\mathrm{M}\) shows signals at \(\delta 146.12,110.75,71.05\), and \(29.88\). Deduce the structural formulas of compounds \(M\) and N.

The line of integration of the two signals in the \({ }^{1} \mathrm{H}-\mathrm{NMR}\) spectrum of a ketone with the molecular formula \(\mathrm{C}_{7} \mathrm{H}_{14} \mathrm{O}\) rises 62 and 10 chart divisions, respectively. Calculate the number of hydrogens giving rise to each signal, and propose a structural formula for this ketone.

Compound \(\mathrm{K}\), molecular formula \(\mathrm{C}_{8} \mathrm{H}_{14} \mathrm{O}\), readily undergoes acid-catalyzed dehydration when warmed with phosphoric acid to give compound L, molecular formula \(\mathrm{C}_{6} \mathrm{H}_{12}\), as the major organic product. The \({ }^{1} \mathrm{H}\)-NMR spectrum of compound \(\mathrm{K}\) shows signals at \(\delta 0.90(\mathrm{t}, 6 \mathrm{H}), 1.12(\mathrm{~s}, 3 \mathrm{H}), 1.38(\mathrm{~s}, 1 \mathrm{H})\), and \(1.48(\mathrm{q}, 4 \mathrm{H})\). The \({ }^{19} \mathrm{C}-\mathrm{NMR}\) spectrum of compound \(\mathrm{K}\) shows signals at \(\delta 72.98,33.72,25.85\), and 8.16. Deduce the structural formulas of compounds \(\mathrm{K}\) and \(\mathrm{L}\).

The natural abundance of \({ }^{19} \mathrm{C}\) is only \(1.1 \%\). Furthermore, its sensitivity in NMR specroscopy (a measure of the energy difference between a spin aligned with or against an applied magnetic field) is only \(1.6 \%\) that of \({ }^{1} \mathrm{H}\). What are the relative signal intensiies expected for the \({ }^{1} \mathrm{H}-\mathrm{NMR}\) and \({ }^{13} \mathrm{C}-\mathrm{NMR}\) spectra of the same sample of \(\mathrm{Si}\left(\mathrm{CH}_{5}\right)_{4}\) ?
See all solutions

Recommended explanations on Chemistry Textbooks

Chemistry Branches

Read Explanation

Physical Chemistry

Read Explanation

Nuclear Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Ionic and Molecular Compounds

Read Explanation

Organic Chemistry

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free