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

Mass Spect:Isotopes

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

Mass Spect:Isotopes

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4:26 minutes

Problem 52

Textbook Question

A compound gives a mass spectrum with essentially only three peaks at m/z = 77 (40%), 112 (100%), and 114 (33%). Identify the compound.

Verified step by step guidance

Analyze the mass spectrum data: The peaks at m/z = 77, 112, and 114 represent the molecular ion and possible fragments. The relative intensities (40%, 100%, and 33%) provide clues about the isotopic composition and structure of the compound.

Focus on the molecular ion peaks at m/z = 112 and 114. The presence of two peaks with a 2 m/z difference and a relative intensity ratio of approximately 3:1 suggests the presence of a chlorine atom. Chlorine has two isotopes, 35Cl and 37Cl, with a natural abundance ratio of about 3:1.

Deduce the molecular formula: The molecular ion peak at m/z = 112 corresponds to the compound containing 35Cl, while the peak at m/z = 114 corresponds to the compound containing 37Cl. This indicates the compound likely contains one chlorine atom.

Examine the fragment peak at m/z = 77: This peak is likely a stable aromatic fragment, such as a phenyl group (C₆H₅⁺), which is common in compounds containing benzene rings.

Combine the information: The compound is likely a chlorobenzene derivative, specifically chlorobenzene (C₆H₅Cl), as it matches the observed mass spectrum with a molecular ion at m/z = 112 (C₆H₅⁻³⁵Cl) and 114 (C₆H₅⁻³⁷Cl), and a fragment peak at m/z = 77 (C₆H₅⁺).

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Key Concepts

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

Mass Spectrometry

Mass spectrometry is an analytical technique used to measure the mass-to-charge ratio of ions. It provides information about the molecular weight and structure of compounds by generating a mass spectrum, which displays the abundance of ions at various mass-to-charge (m/z) values. The peaks in the spectrum correspond to different ions, allowing chemists to deduce the molecular composition of the sample.

Isotopic Patterns

Isotopic patterns arise from the presence of isotopes in elements, which can lead to multiple peaks in a mass spectrum. For example, carbon has isotopes like 12C and 13C, which can create peaks at different m/z values. Understanding these patterns helps in identifying the molecular formula of a compound, as the relative intensities of the peaks can indicate the number of each type of atom present.

Molecular Ion Peak

The molecular ion peak in a mass spectrum represents the intact molecule of the compound being analyzed, typically observed at the highest m/z value. This peak is crucial for determining the molecular weight of the compound. In the given spectrum, the peak at m/z = 112 likely corresponds to the molecular ion, while the other peaks can indicate fragment ions or isotopes, aiding in the identification of the compound.

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Related Practice

Multiple Choice

Propose the number of carbons for a compound that exhibits the following peak in its mass spectrum:

(M)+• at m/z = 72, relative height = 38.3% of base peak

(M+1)+• at m/z = 73, relative height = 1.7% of base peak

Multiple Choice

Predict the approximate height of the (M + 1) peak for the molecule icosane, molecular formula C₂₀H₄₂.

Multiple Choice

1,4-dichlorobenzene is used as an insecticide and has the formula C₆H₄Cl₂. What would be the approximate relative heights of M, M+2, and M+4 peaks. For simplicity assume that all carbon atoms are ¹²C and the ³⁵Cl:³⁷Cl ratio is 75:25.

Textbook Question

Identify which of these four mass spectra indicate the presence of sulfur, chlorine, bromine, iodine, or nitrogen. Suggest a molecular formula for each.

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Textbook Question

Predict the relative intensities of the molecular ion peak, the M+2 peak, and the M+4 peak for a compound that contains two bromine atoms.

Textbook Question

Besides the molecular mass, how do you know that the fragment that gives rise to the peak at m/z 111 in the mass spectrum for 1-bromo-4-chlorobenzene contains only chlorine?

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Textbook Question

What ratio of M, M + 2 , M + 4 and would you expect for 1,6-dibromohexane?

Textbook Question

The presence of what atom is indicated by the following mass spectrum?

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