Predict the approximate height of the (M + 1) peak for the molecule icosane, molecular formula C₂₀H₄₂.

• A. 11
• B. 44
• C. 50
• D. 22

Answer: (D)

Verified step by step guidance

1. Understand that the (M + 1) peak in mass spectrometry is due to the presence of isotopes, primarily carbon-13 (13C), which is about 1.1% abundant compared to carbon-12 (12C).
2. Calculate the contribution of 13C to the (M + 1) peak. Since icosane has 20 carbon atoms, the probability of one of these being 13C is approximately 20 times the natural abundance of 13C, which is 1.1%.
3. Express the calculation using MathML: $20\times 1.1\%$. This gives the approximate percentage of the (M + 1) peak relative to the molecular ion peak (M).
4. Consider that hydrogen isotopes (such as deuterium) are less abundant and typically do not significantly contribute to the (M + 1) peak for hydrocarbons like icosane.
5. Conclude that the calculated percentage from the carbon-13 contribution gives the approximate height of the (M + 1) peak relative to the molecular ion peak.