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The rule you generated in Question 14b for finding the [M]* peak on the mass spectrum of an unknown molecule does not work very well if there is a Br or Cl in the molecule. Shown below are spectra of various compounds containing one Br or Cl. a. Find the [M] and [M+2]* peak on each spectrum.

The rule you generated in Question 14b for finding the [M]* peak on the mass spectrum of an unknown molecule does not work very well if there is a Br or Cl in the molecule. Shown below are spectra of various compounds containing one Br or Cl. a. Find the [M] and [M+2]* peak on each spectrum.

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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**Mass Spectrometry of Compounds Containing Br or Cl** **27.** When analyzing mass spectra, the presence of Br or Cl in a molecule complicates identifying the [M]⁺ peak. Below are spectra of compounds each containing one Br or Cl atom. **a. Identifying [M]⁺ and [M+2]⁺ Peaks:** 1. **Top Left Spectrum:** - Compound has Br. - The [M]⁺ peak is located at a specific m/z value, and the [M+2]⁺ peak is observed at two m/z units higher with almost equal intensity due to the natural abundance of bromine isotopes. 2. **Top Right Spectrum:** - Compound has Cl. - The [M]⁺ peak appears at a particular m/z, with the [M+2]⁺ peak having about one-third the intensity compared to the [M]⁺ peak, reflecting the natural abundance of chlorine isotopes. 3. **Bottom Left Spectrum:** - Another compound with Br. - Similar pattern observed as in the first spectrum with [M]⁺ and [M+2]⁺ peaks. 4. **Bottom Right Spectrum:** - Compound has Cl. - Features a lesser intense [M+2]⁺ peak, typical for chlorine-containing compounds. **b. Quick Identification Rules:** 1. **One Cl atom:** - Look for an [M+2]⁺ peak with approximately one-third the intensity of the [M]⁺ peak. 2. **One Br atom:** - Identify the [M+2]⁺ peak with similar intensity to the [M]⁺ peak. *Note: The complexity increases with more than one Cl or Br, so stick to single instances for simplicity.* **c. New Rule for [M]⁺ Peak with Br or Cl:** - Adjust for the intense [M+2]⁺ peaks by recognizing that Cl and Br isotopes significantly contribute to this pattern. Use isotopic patterns (Cl at 1:3 and Br at 1:1) for peak validation. **28. Peaks Beyond [M+2]⁺:** - Each spectrum includes an [M+3]⁺ peak, resulting from the presence of isotopes like ¹³C and either ³⁷Cl or ⁸
Transcribed Image Text:**Mass Spectrometry of Compounds Containing Br or Cl** **27.** When analyzing mass spectra, the presence of Br or Cl in a molecule complicates identifying the [M]⁺ peak. Below are spectra of compounds each containing one Br or Cl atom. **a. Identifying [M]⁺ and [M+2]⁺ Peaks:** 1. **Top Left Spectrum:** - Compound has Br. - The [M]⁺ peak is located at a specific m/z value, and the [M+2]⁺ peak is observed at two m/z units higher with almost equal intensity due to the natural abundance of bromine isotopes. 2. **Top Right Spectrum:** - Compound has Cl. - The [M]⁺ peak appears at a particular m/z, with the [M+2]⁺ peak having about one-third the intensity compared to the [M]⁺ peak, reflecting the natural abundance of chlorine isotopes. 3. **Bottom Left Spectrum:** - Another compound with Br. - Similar pattern observed as in the first spectrum with [M]⁺ and [M+2]⁺ peaks. 4. **Bottom Right Spectrum:** - Compound has Cl. - Features a lesser intense [M+2]⁺ peak, typical for chlorine-containing compounds. **b. Quick Identification Rules:** 1. **One Cl atom:** - Look for an [M+2]⁺ peak with approximately one-third the intensity of the [M]⁺ peak. 2. **One Br atom:** - Identify the [M+2]⁺ peak with similar intensity to the [M]⁺ peak. *Note: The complexity increases with more than one Cl or Br, so stick to single instances for simplicity.* **c. New Rule for [M]⁺ Peak with Br or Cl:** - Adjust for the intense [M+2]⁺ peaks by recognizing that Cl and Br isotopes significantly contribute to this pattern. Use isotopic patterns (Cl at 1:3 and Br at 1:1) for peak validation. **28. Peaks Beyond [M+2]⁺:** - Each spectrum includes an [M+3]⁺ peak, resulting from the presence of isotopes like ¹³C and either ³⁷Cl or ⁸
**Text for Educational Website:** --- **29.** On the mass spectrum of hexane in this activity, the [M]⁺ peak (at m/z = 86) has an intensity of 10. Calculate the expected intensity of the [M+1] peak in this spectrum. --- **30.** Calculate the molecular weight of each of the following molecules using the most common isotope of each element: - Ammonia (NH₃) - Acetamide (H₃C(C=O)NH₂) - Methylamine (H-C-NH-CH₃) - Hydrogen cyanide (N≡C-H) - Acetonitrile (CH₃-C≡N) [Structural diagrams of the mentioned molecules] --- **31.** What do the molecular weights in the previous question have in common with one another that set them apart from ALL the molecular weights in the [M]⁺ column in Model 6? --- **Memorization Task L2.5: Nitrogen Rule** It turns out that any molecule with an odd number of nitrogen atoms (1, 3, 5, etc.) will have an odd molecular weight and vice versa. This "nitrogen rule" is a consequence of the fact that ¹⁴N is the only common organic element that makes an odd number of bonds but has an even molecular weight. --- **32.** Give examples of two very common elements that make an even number of bonds and whose most common isotope has an even molecular weight. --- **33.** Give an example of at least one element that makes an odd number of bonds and whose most common isotope has an odd molecular weight. ---
Transcribed Image Text:**Text for Educational Website:** --- **29.** On the mass spectrum of hexane in this activity, the [M]⁺ peak (at m/z = 86) has an intensity of 10. Calculate the expected intensity of the [M+1] peak in this spectrum. --- **30.** Calculate the molecular weight of each of the following molecules using the most common isotope of each element: - Ammonia (NH₃) - Acetamide (H₃C(C=O)NH₂) - Methylamine (H-C-NH-CH₃) - Hydrogen cyanide (N≡C-H) - Acetonitrile (CH₃-C≡N) [Structural diagrams of the mentioned molecules] --- **31.** What do the molecular weights in the previous question have in common with one another that set them apart from ALL the molecular weights in the [M]⁺ column in Model 6? --- **Memorization Task L2.5: Nitrogen Rule** It turns out that any molecule with an odd number of nitrogen atoms (1, 3, 5, etc.) will have an odd molecular weight and vice versa. This "nitrogen rule" is a consequence of the fact that ¹⁴N is the only common organic element that makes an odd number of bonds but has an even molecular weight. --- **32.** Give examples of two very common elements that make an even number of bonds and whose most common isotope has an even molecular weight. --- **33.** Give an example of at least one element that makes an odd number of bonds and whose most common isotope has an odd molecular weight. ---
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