1. What is the Rule of 13?

The Rule of 13 is a simple method used in mass spectrometry to estimate possible molecular formulas for organic compounds based on their molecular mass. It provides a quick way to generate candidate formulas for further analysis.

2. How Does the Calculator Work?

The calculator uses the Rule of 13 equation:

Where:

• \( MF \) — Molecular formula
• \( M \) — Molecular mass
• \( n \) — Integer part of M/13
• \( r \) — Remainder of M divided by 13

Explanation: The rule assumes a base formula of hydrocarbons (CₙHₙ) with mass 13n, then adds the remainder as additional hydrogen atoms.

3. Importance of Rule of 13

Details: This rule provides a starting point for molecular formula determination in mass spectrometry, particularly useful for organic compounds containing primarily carbon and hydrogen.

4. Using the Calculator

Tips: Enter the molecular mass as a whole number. The calculator will compute the base hydrocarbon formula using the Rule of 13.

5. Frequently Asked Questions (FAQ)

Q1: What types of compounds does this rule work best for?
A: The Rule of 13 works best for hydrocarbons and compounds containing primarily carbon and hydrogen atoms.

Q2: How accurate is the Rule of 13?
A: This is an estimation method that provides a starting point. Actual molecular formulas may contain heteroatoms (O, N, S, etc.) that require adjustment.

Q3: What if my compound contains heteroatoms?
A: For compounds with heteroatoms, the base formula needs to be adjusted by replacing CH₄ groups with appropriate heteroatom equivalents (e.g., O replaces CH₄, NH replaces CH₂, etc.).

Q4: What are the limitations of this rule?
A: The rule doesn't account for double bond equivalents, ring structures, or specific functional groups. It's a simplified approach for initial estimation.

Q5: When should I use this rule?
A: Use this rule as a quick screening tool in mass spectrometry to generate possible molecular formulas before performing more detailed analysis.