key term - [M - 1]+

Definition

[M - 1]+ is a key term in the context of the spectroscopy of alcohols and phenols. It refers to the molecular ion peak that is observed in mass spectrometry, where the mass-to-charge ratio (m/z) is one less than the molecular mass (M) of the analyte. This peak provides important information about the molecular weight and structure of the compound being analyzed.

5 Must Know Facts For Your Next Test

1. The [M - 1]+ peak is often the base peak (the most intense peak) in the mass spectrum of alcohols and phenols, as these compounds readily lose a hydrogen atom during ionization.
2. The presence and relative intensity of the [M - 1]+ peak can provide information about the type and position of functional groups in the molecule, as well as the degree of unsaturation.
3. The [M - 1]+ peak is particularly useful in the analysis of alcohols, as it helps distinguish them from other classes of compounds, such as alkanes or alkenes, which do not typically exhibit this peak.
4. The intensity of the [M - 1]+ peak can be affected by factors such as the ionization method, the presence of other functional groups, and the stability of the resulting radical cation.
5. The [M - 1]+ peak is often used in conjunction with other mass spectrometric data, such as fragmentation patterns and isotopic distributions, to confirm the identity and structure of alcohols and phenols.

Review Questions

• Explain the significance of the [M - 1]+ peak in the mass spectrum of alcohols and phenols.
  • The [M - 1]+ peak in the mass spectrum of alcohols and phenols is significant because it provides information about the molecular weight and structure of the compound. This peak arises due to the ready loss of a hydrogen atom from the molecular ion during the ionization process, which is characteristic of these functional groups. The presence and relative intensity of the [M - 1]+ peak can help distinguish alcohols and phenols from other classes of compounds and provide insights into the type and position of the functional groups within the molecule.
• Describe how the [M - 1]+ peak can be used to differentiate alcohols and phenols from other classes of compounds in mass spectrometry.
  • The [M - 1]+ peak is particularly useful in distinguishing alcohols and phenols from other classes of compounds, such as alkanes or alkenes, which do not typically exhibit this peak. The presence and relative intensity of the [M - 1]+ peak can provide information about the type and position of the functional groups within the molecule. For example, the [M - 1]+ peak is often the base peak in the mass spectrum of alcohols and phenols, as these compounds readily lose a hydrogen atom during ionization. This characteristic fragmentation pattern can help identify the compound and differentiate it from other classes of compounds that may have different fragmentation pathways.
• Analyze how the [M - 1]+ peak can be used in conjunction with other mass spectrometric data to confirm the identity and structure of alcohols and phenols.
  • The [M - 1]+ peak is often used in combination with other mass spectrometric data, such as fragmentation patterns and isotopic distributions, to confirm the identity and structure of alcohols and phenols. The [M - 1]+ peak provides information about the molecular weight of the compound, while the fragmentation pattern can give insights into the structure and the presence of functional groups. Additionally, the isotopic distribution of the [M - 1]+ peak can provide further confirmation of the molecular formula. By considering the [M - 1]+ peak alongside these other mass spectrometric data points, analysts can more confidently determine the identity and structural features of alcohols and phenols, which is crucial for their accurate identification and characterization.

Related terms

Molecular Ion Peak:

The peak in a mass spectrum that corresponds to the molecular ion of the analyte, which has a mass-to-charge ratio (m/z) equal to the molecular mass (M).

Fragmentation: The process by which the molecular ion undergoes further breakdown into smaller fragment ions, providing information about the structure of the compound.

Mass Spectrometry:

An analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio, allowing for the determination of the molecular mass and structure of the analyte.