key term - [M - 29]+

Definition

[M - 29]+ is a key ion fragment observed in the mass spectra of alcohols and phenols, resulting from the loss of the alkyl or aryl group (R) from the molecular ion [M]+. This characteristic fragment provides important structural information about the parent compound.

5 Must Know Facts For Your Next Test

1. The [M - 29]+ ion is a characteristic fragment for alcohols and phenols, as it results from the loss of the alkyl or aryl group (R) from the molecular ion.
2. The mass of the [M - 29]+ ion is 29 mass units less than the molecular ion [M]+, corresponding to the loss of the CH3 group.
3. The relative abundance of the [M - 29]+ ion in the mass spectrum provides information about the size and nature of the alkyl or aryl group (R) attached to the alcohol or phenol.
4. The presence and intensity of the [M - 29]+ ion can be used to differentiate between primary, secondary, and tertiary alcohols, as well as distinguish alcohols from phenols.
5. The fragmentation pattern leading to the [M - 29]+ ion is a useful tool for structural elucidation and identification of unknown alcohol and phenol compounds.

Review Questions

• Explain the significance of the [M - 29]+ ion in the mass spectra of alcohols and phenols.
  • The [M - 29]+ ion is a characteristic fragment observed in the mass spectra of alcohols and phenols, resulting from the loss of the alkyl or aryl group (R) from the molecular ion [M]+. The presence and relative abundance of this ion provide important structural information about the parent compound, such as the size and nature of the substituent group. The [M - 29]+ ion can be used to differentiate between primary, secondary, and tertiary alcohols, as well as distinguish alcohols from phenols, which is crucial for the structural elucidation and identification of unknown alcohol and phenol compounds.
• Describe the relationship between the [M - 29]+ ion and the molecular ion [M]+ in the mass spectra of alcohols and phenols.
  • The [M - 29]+ ion is directly related to the molecular ion [M]+ observed in the mass spectrum of alcohols and phenols. The [M - 29]+ ion is formed by the loss of the alkyl or aryl group (R) from the molecular ion during the fragmentation process in the mass spectrometer. The mass of the [M - 29]+ ion is 29 mass units less than the molecular ion [M]+, corresponding to the loss of the CH3 group. The relative abundance of the [M - 29]+ ion compared to the molecular ion [M]+ provides information about the size and nature of the substituent group (R) attached to the alcohol or phenol, which is crucial for structural elucidation and identification of these compounds.
• Analyze how the [M - 29]+ ion can be used to differentiate between various types of alcohols and phenols.
  • The [M - 29]+ ion can be used to differentiate between primary, secondary, and tertiary alcohols, as well as distinguish alcohols from phenols. The relative abundance of the [M - 29]+ ion compared to the molecular ion [M]+ is influenced by the size and nature of the alkyl or aryl group (R) attached to the alcohol or phenol. For primary alcohols, the [M - 29]+ ion is typically the base peak, indicating a larger alkyl group. For secondary and tertiary alcohols, the [M - 29]+ ion is less abundant, as the alkyl group is smaller. In the case of phenols, the [M - 29]+ ion is less prominent compared to alcohols, as the aryl group is more stable and less likely to be lost during fragmentation. By analyzing the presence and intensity of the [M - 29]+ ion, along with other fragmentation patterns, the structural features of alcohols and phenols can be elucidated and used for their identification.

Related terms

Molecular Ion [M]+: The parent ion or molecular ion observed in a mass spectrum, representing the intact, unfragmented molecule.

Fragmentation: The process by which a molecule breaks apart into smaller, charged fragments during ionization in a mass spectrometer.

Alkyl Group (R): The hydrocarbon substituent attached to the alcohol or phenol functional group, which is lost as a neutral fragment during fragmentation.