What is represented by the molecular ion peak on a mass spectrum?

The molecular ion peak on a mass spectrum corresponds to the relative molecular mass of the compound being analyzed. This peak represents the intact molecule of the substance that has not undergone fragmentation during the ionization process. When a compound is ionized in a mass spectrometer, it may gain or lose electrons, forming positively charged ions. The molecular ion, often denoted as [M]+, reflects the total mass of the molecule including all its atoms and provides crucial information for determining the molecular formula.

The height or intensity of this peak does not necessarily indicate the most abundant isotope but rather the presence of the molecular ion itself. Additionally, it is not typically the lowest peak on the spectrum, as many fragments can produce smaller peaks due to their lower mass and higher abundance. Lastly, the molecular ion peak does not represent a mixture of compounds, as it specifically relates to a single molecular entity. Therefore, understanding the significance of the molecular ion peak helps in deducing important details about the molecular structure and composition of the substance under study.