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Ch. 14 - Structural Identification 1: Infrared Spectroscopy and Mass Spectrometry
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Mullins 1st EditionCh. 14 - Structural Identification 1: Infrared Spectroscopy and Mass Spectrometry문제 34
13장, 문제 34

The molecular ion (M) is significant in the mass spectrum of benzyl fluoride, but it is barely present in the mass spectrum of benzyl iodide. Why might this be the case?
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검증된 단계별 안내
1
Consider the concept of the molecular ion (M) in mass spectrometry, which is the ion formed by the removal of an electron from a molecule, resulting in a radical cation. This ion is significant because it represents the molecular weight of the compound.
Understand that the stability of the molecular ion is crucial for its presence in the mass spectrum. More stable ions are more likely to be detected.
Analyze the bond strengths in benzyl fluoride and benzyl iodide. The C-F bond in benzyl fluoride is much stronger than the C-I bond in benzyl iodide. This difference in bond strength affects the stability of the molecular ion.
Recognize that the weaker C-I bond in benzyl iodide makes the molecular ion less stable and more prone to fragmentation, leading to its reduced presence in the mass spectrum.
Conclude that the stronger C-F bond in benzyl fluoride contributes to a more stable molecular ion, which is why it is more prominent in the mass spectrum compared to benzyl iodide.

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주요 개념

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Molecular Ion Formation

In mass spectrometry, the molecular ion (M) is formed when a molecule loses an electron, resulting in a positively charged ion. This ion represents the entire molecule and is crucial for determining the molecular weight. The stability of the molecular ion can vary depending on the structure and the elements present in the molecule.
추천 영상:
가이드 코스
3:39
Metal Ion Catalysis Concept 1

Bond Strength and Stability

The bond strength between carbon and halogens (like fluorine and iodine) affects the stability of the molecular ion. Carbon-fluorine bonds are stronger than carbon-iodine bonds, making the molecular ion of benzyl fluoride more stable and detectable in mass spectrometry, whereas the weaker carbon-iodine bond in benzyl iodide leads to rapid fragmentation.
추천 영상:
03:43
The radical stability trend.

Fragmentation Patterns

Fragmentation in mass spectrometry occurs when the molecular ion breaks into smaller ions. The tendency to fragment depends on the stability of the molecular ion and the bonds within the molecule. Benzyl iodide's molecular ion is less stable due to the weak C-I bond, leading to significant fragmentation and a reduced presence of the molecular ion peak in its mass spectrum.
추천 영상:
08:06
Common Splitting Patterns
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교과서 질문

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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교과서 질문

Suggest three ways that the following tertiary amine can fragment by α-cleavage. At which m/z would you expect to see peaks corresponding to these fragments?

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The molecule that gave the mass spectrum shown here contains a halogen. Which halogen is present?

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교과서 질문

In the mass spectrum of hexan-3-ol, identify the fragments arising from two α-cleavage fragmentations and one dehydration fragmentation.

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교과서 질문

Match each of the four IR spectra to one of the given compounds. [One of the compounds does not match a spectrum.]

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교과서 질문

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

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