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A compound of molecular formula \(\mathrm{C}_{8} \mathrm{H}_{14} \mathrm{O}_{2}\) gives three NMR signals having the indicated integration values: signal [A] 14 units, signal [B] 12 units, and signal [C] 44 units. How many protons give rise to each signal?

Short Answer

Expert verified
Signals A, B, and C are from 3, 2, and 9 hydrogens, respectively.

Step by step solution

01

Understanding the total number of hydrogens

The molecular formula \( \mathrm{C}_{8} \mathrm{H}_{14} \mathrm{O}_{2} \) indicates that there are 14 hydrogen atoms in the compound. NMR (Nuclear Magnetic Resonance) integration values correspond directly to the number of protons (hydrogens) contributing to each signal. Thus, the sum of protons from signals A, B, and C must equal 14.
02

Calculating proportional contributions

Add the integration values: 14 (signal A) + 12 (signal B) + 44 (signal C) = 70. This total is proportional to 14 hydrogens, so each unit of integration represents \( \frac{14}{70} \) (or \( \frac{1}{5} \)) of a proton.
03

Assigning number of hydrogens per signal

For each signal, multiply its integration value by \( \frac{1}{5} \): - Signal A: \( 14 \times \frac{1}{5} = 2.8 \approx 3 \) hydrogens- Signal B: \( 12 \times \frac{1}{5} = 2.4 \approx 2 \) hydrogens- Signal C: \( 44 \times \frac{1}{5} = 8.8 \approx 9 \) hydrogensSince the total number of hydrogens must be an integer, check that the sum 3 + 2 + 9 equals 14 hydrogens, which is correct.

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Key Concepts

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

Proton Integration
Proton integration in NMR spectroscopy is a crucial step that connects the observed signals to the number of hydrogen atoms (protons) in a molecule. Each signal corresponds to a specific set of equivalent protons in the molecule. The area under each signal is directly proportional to the number of protons causing that signal.

For example, in our problem involving the molecular formula \(\mathrm{C}_8\mathrm{H}_{14}\mathrm{O}_2\), we have three integration values: 14, 12, and 44. These values must sum up to account for the 14 hydrogen atoms in the compound. Therefore, understanding the ratio of these values helps determine how many protons give rise to each signal. When the total of these integration units is 70, we calculate that each unit represents \(\frac{1}{5}\) of a proton, which aids in determining the contribution from each signal.

Effectively using proton integration allows chemists to analyze complex mixtures by identifying specific hydrogen environments within a molecule. This makes proton integration an invaluable tool for chemical identification and structural analysis.
Hydrogen Counting
Hydrogen counting is an essential aspect of NMR spectroscopy that ensures the calculated distribution of protons matches the molecular formula. It verifies that all protons in the compound contribute to the observed NMR signals based on their integration values.

In our exercise, we start by identifying that there are 14 total hydrogen atoms based on the molecular formula \(\mathrm{C}_{8}\mathrm{H}_{14}\mathrm{O}_{2}\). After determining the proportion each integration unit represents, it's pivotal to assign the correct number of protons to each NMR signal: 2.8 protons for signal [A], 2.4 for signal [B], and 8.8 for signal [C]. Rounding these to the nearest whole number gives a clear count: 3, 2, and 9 protons, respectively.

Achieving entire numbers in hydrogen counting is critical since it confirms the integrity of the molecular analysis. It ensures correct structural interpretation, which is fundamental for understanding chemical identity and behavior.
Molecular Formula Analysis
Molecular formula analysis involves examining an organic compound's given formula to determine the total number of atoms and their type. This fundamental step is crucial for deducing potential structures and understanding how these atoms are distributed across the molecule.

In this context, \(\mathrm{C}_{8}\mathrm{H}_{14}\mathrm{O}_{2}\) provides the backbone for our NMR analysis, foretelling the number of carbons, hydrogens, and oxygens. Analyzing the integration data follows this step, linking the molecular formula to real-world observations provided by NMR signals. This analysis allows us to validate that our count of hydrogens from the signals aligns with the ones predicted by the molecular formula.

By closely examining the molecular formula, chemists can predict possible functional groups or structural isomers, offering a guide for interpreting NMR data. Thus, molecular formula analysis stands as a cornerstone in the spectroscopic evaluation and structural elucidation of unknown compounds.

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Most popular questions from this chapter

The \({ }^{1} \mathrm{H}\) NMR spectrum of \(\mathrm{CH}_{3} \mathrm{OH}\) recorded on a \(500 \mathrm{MHz}\) NMR spectrometer consists of two signals, one due to the \(\mathrm{CH}_{3}\) protons at \(1715 \mathrm{~Hz}\) and one due to the OH proton at \(1830 \mathrm{~Hz}\), both measured downfield from TMS. (a) Calculate the chemical shift of each absorption. (b) Do the \(\mathrm{CH}_{3}\) protons absorb upfield or downfield from the OH proton?

Identify products \(\mathbf{A}\) and \(\mathbf{B}\) from the given \({ }^{1} \mathrm{H}\) NMR data. a. Treatment of \(\mathrm{CH}_{2}=\mathrm{CHCOCH}_{3}\) with one equivalent of HCl forms compound A. A exhibits the following absorptions in its \({ }^{1} \mathrm{H}\) NMR spectrum: \(2.2\) (singlet, \(3 \mathrm{H}\) ), \(3.05\) (triplet, \(2 \mathrm{H}\) ), and \(3.6\) (triplet, \(2 \mathrm{H}\) ) ppm. What is the structure of \(\mathbf{A}\) ? b. Treatment of acetone \(\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{O}\right]\) with dilute aqueous base forms \(\mathrm{B}\). Compound \(\mathrm{B}\) exhibits four singlets in its \({ }^{1} \mathrm{H}\) NMR spectrum at \(1.3(6 \mathrm{H}), 2.2(3 \mathrm{H}), 2.5(2 \mathrm{H})\), and \(3.8(1 \mathrm{H}) \mathrm{ppm}\). What is the structure of \(\mathbf{B}\) ?

When 2 -bromo-3,3-dimethylbutane is treated with \(\mathrm{K}^{+-} \mathrm{OC}\left(\mathrm{CH}_{3}\right)_{3}\), a single product A having molecular formula \(\mathrm{C}_{6} \mathrm{H}_{12}\) is formed. When 3,3-dimethyl-2-butanol is treated with \(\mathrm{H}_{2} \mathrm{SO}_{4}\), the major product \(\mathrm{B}\) has the same molecular formula. Given the following 'H NMR data, what are the structures of \(\mathbf{A}\) and \(\mathbf{B}\) ? Explain in detail the splitting patterns observed for the three split signals in A, \({ }^{1}\) H NMR of A: \(1.01\) (singlet, \(9 \mathrm{H}\) ), \(4.82\) (doublet of doublets, \(1 \mathrm{H}, J=10,1.7 \mathrm{~Hz}\) ), \(4.93\) (doublet of doublets, \(1 \mathrm{H}\), \(J=18,1.7 \mathrm{~Hz}\) ), and \(5.83\) (doublet of doublets, \(1 \mathrm{H}, J=18,10 \mathrm{~Hz}\) ) ppm 'H NMR of B: \(1.60\) (singlet) ppm

Which ether(s) having molecular formula \(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}\) give \(\mathrm{a}^{1} \mathrm{H}\) NMR spectrum that fits each description: (a) The spectrum consists of only two singlets. (b) In addition to other signals, the spectrum contains a singlet in the \(3-4\) ppm region. (c) In addition to other signals, the spectrum contains a septet in the \(3-4\) ppm region. (d) In addition to other signals, the spectrum contains a doublet in the \(1-2\) ppm region. (e) The spectrum contains six signals.

How many \({ }^{1} \mathrm{H}\) NMR signals does each compound show? a. \(\mathrm{CH}_{3} \mathrm{CH}_{3}\) c. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) e. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) g. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}\) b. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\) d. \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}\left(\mathrm{CH}_{3}\right)_{2}\) f. \(\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\) h. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\)

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