Chapter 14: Problem 16
The base peak in the mass spectrum of propanone (acetone) occurs at \(m / z 43\). What cation does this peak represent?
Short Answer
Expert verified
Answer: The cation responsible for the m/z peak at 43 in the mass spectrum of propanone is CH3CO+ (the acylium ion).
Step by step solution
01
Structure of Propanone
First, we need to know the structure of propanone. Propanone, also known as acetone, is an organic compound with the molecular formula C3H6O. Its structural formula can be written as CH3COCH3.
02
Fragmentation of Propanone
When propanone is subjected to mass spectrometry, it undergoes fragmentation to produce different cations. Various bonds within the molecule can be broken during this process, leading to the formation of different cationic species.
03
Possible fragments of Propanone
Some of the possible fragments of propanone are:
1. CH3+ (m/z = 15)
2. CH3CO+ (m/z = 43)
3. CH3CH2+ (m/z = 29)
04
Identify the cation responsible for the m/z peak at 43
We are asked to identify the fragment with an m/z ratio of 43. From the previous step, we found that CH3CO+ has an m/z ratio of 43. Therefore, the cation responsible for the base peak at m/z 43 in the mass spectrum of propanone is CH3CO+ (the acylium ion).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Propanone
Propanone, commonly known as acetone, is one of the simplest ketones. It's a clear, volatile liquid with a distinctive odor. This compound is widely used in industries and households as a solvent. The chemical formula for propanone is \( \text{C}_3\text{H}_6\text{O} \), and its structural formula is depicted as \( \text{CH}_3\text{COCH}_3 \).
In the structure of propanone, there is a central carbon atom double-bonded to an oxygen atom, creating a carbonyl group. This configuration is responsible for many of its chemical properties. Understanding the structure of propanone is crucial when discussing its behavior in mass spectrometry because different parts of this molecule can lead to the creation of various fragments during analysis.
In the structure of propanone, there is a central carbon atom double-bonded to an oxygen atom, creating a carbonyl group. This configuration is responsible for many of its chemical properties. Understanding the structure of propanone is crucial when discussing its behavior in mass spectrometry because different parts of this molecule can lead to the creation of various fragments during analysis.
Fragmentation
In mass spectrometry, fragmentation is a process where molecules are broken down into smaller pieces after being ionized. When propanone is subjected to this technique, it undergoes fragmentation. This means that the chemical bonds within the molecule break apart, producing different ionic fragments.
Fragmentation occurs due to the high-energy conditions inside the mass spectrometer, where molecules lose electrons and become charged. The breaking of bonds and formation of fragments give rise to the peaks seen in a mass spectrum. Each peak corresponds to a different fragment with a specific mass-to-charge ratio (\(m/z\)) that helps in identifying the structure of the original molecule.
This step is essential in determining the composition and confirming the presence of specific functional groups in a compound, such as the carbonyl group in propanone.
Fragmentation occurs due to the high-energy conditions inside the mass spectrometer, where molecules lose electrons and become charged. The breaking of bonds and formation of fragments give rise to the peaks seen in a mass spectrum. Each peak corresponds to a different fragment with a specific mass-to-charge ratio (\(m/z\)) that helps in identifying the structure of the original molecule.
This step is essential in determining the composition and confirming the presence of specific functional groups in a compound, such as the carbonyl group in propanone.
Acylium Ion
The acylium ion is a specific fragment that results from the fragmentation of propanone during mass spectrometry. This ion has the chemical formula \( \text{CH}_3\text{CO}^+ \) and is characterized by its distinct structure, where the carbon atom is bonded to an oxygen atom in a way that forms a positively charged species.
In the mass spectrum of propanone, the acylium ion is responsible for the base peak at \(m/z = 43\). This peak is the most intense one in the spectrum and provides critical clues about the fragmentation pattern of the molecule. The formation of the acylium ion involves the cleavage of bonds within propanone, specifically resulting from the loss of a methyl group (\(\text{CH}_3\)).
In the mass spectrum of propanone, the acylium ion is responsible for the base peak at \(m/z = 43\). This peak is the most intense one in the spectrum and provides critical clues about the fragmentation pattern of the molecule. The formation of the acylium ion involves the cleavage of bonds within propanone, specifically resulting from the loss of a methyl group (\(\text{CH}_3\)).
- The acylium ion is significant because its presence generally indicates the loss of a neutral fragment from the original molecule, which helps in elucidating the structure of larger organic molecules.
m/z Ratio
The term \(m/z\) stands for mass-to-charge ratio. It's a fundamental concept in mass spectrometry, used to describe and identify ions based on their size and charge. In a spectrum, each peak corresponds to a different fragment of the analyzed compound, with the horizontal axis representing the \(m/z\) ratio and the vertical axis the abundance.
For the propanone example, the \(m/z\) ratio of 43 corresponds to the acylium ion (\(\text{CH}_3\text{CO}^+\)). This ratio provides insight into which specific fragment of the molecule is responsible for that peak. Understanding \(m/z\) ratios is key to interpreting mass spectrometric data because it allows chemists to deduce the possible molecular fragments, identifying their composition and helping in the reconstruction of the parent molecule.
For the propanone example, the \(m/z\) ratio of 43 corresponds to the acylium ion (\(\text{CH}_3\text{CO}^+\)). This ratio provides insight into which specific fragment of the molecule is responsible for that peak. Understanding \(m/z\) ratios is key to interpreting mass spectrometric data because it allows chemists to deduce the possible molecular fragments, identifying their composition and helping in the reconstruction of the parent molecule.
- In practice, \(m/z\) ratios are used to pinpoint characteristic fragments, acting as a molecular "fingerprint" in qualitative analysis.
- It ensures accuracy in determining molecular weights and verifying composition, which is crucial in both academic research and various industrial applications.
