Skip to main content
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: 9780137566471Non è quello che usi tu?Cambia libro di testo
Capitolo 13, Problema 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?
<IMAGE>

Guida verificata passo dopo passo
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.

Risposta video verificata per un problema simile:

Questa soluzione video è stata consigliata dai nostri tutor come utile per risolvere questo problema.

Concetti chiave

Ecco i concetti essenziali che devi comprendere per rispondere correttamente alla domanda.

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.
Video consigliato:
Percorso guidato
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.
Video consigliato:
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.
Video consigliato:
08:06
Common Splitting Patterns