Degree of Unsaturation Calculator

Calculate the number of rings and double bonds in organic molecules from molecular formula

Degree of Unsaturation (DBE): (2C + 2 + N - H - X) / 2
Where C = carbons, H = hydrogens, N = nitrogens, X = halogens (F, Cl, Br, I)
Oxygen and sulfur are ignored in this formula.

Optional - enter 0 if none

Optional - enter 0 if none

Understanding Degree of Unsaturation

The degree of unsaturation (also called the index of hydrogen deficiency or double bond equivalents - DBE) is a crucial concept in organic chemistry that helps determine the number of rings and/or multiple bonds present in a molecule based solely on its molecular formula.

The Degree of Unsaturation Formula

DBE = (2C + 2 + N - H - X) / 2

Index of Hydrogen Deficiency

C = Number of carbon atoms

Count all carbon atoms in the molecular formula

H = Number of hydrogen atoms

Count all hydrogen atoms

N = Number of nitrogen atoms

Nitrogen adds to unsaturation (trivalent)

X = Number of halogens (F, Cl, Br, I)

Halogens substitute for hydrogen (monovalent)

Note: Oxygen and sulfur are ignored

Divalent atoms don't affect the calculation

What Each DBE Unit Represents

🔷

1 Ring = 1 DBE

Cyclopropane, cyclohexane, etc.

⚡

1 Double Bond = 1 DBE

C=C, C=O, C=N, N=N

⚡⚡

1 Triple Bond = 2 DBE

C≡C, C≡N

Practical Examples

Benzene (C₆H₆)

DBE = (2×6 + 2 + 0 - 6 - 0) / 2 = (12 + 2 - 6) / 2 = 8 / 2 = 4

Benzene has 1 ring + 3 double bonds = 4 DBE ✓

Acetone (C₃H₆O)

DBE = (2×3 + 2 + 0 - 6 - 0) / 2 = (6 + 2 - 6) / 2 = 2 / 2 = 1

Acetone has 1 C=O double bond = 1 DBE ✓ (Note: O is ignored)

Cyclohexene (C₆H₁₀)

DBE = (2×6 + 2 + 0 - 10 - 0) / 2 = (12 + 2 - 10) / 2 = 4 / 2 = 2

Cyclohexene has 1 ring + 1 double bond = 2 DBE ✓

Propyne (C₃H₄)

DBE = (2×3 + 2 + 0 - 4 - 0) / 2 = (6 + 2 - 4) / 2 = 4 / 2 = 2

Propyne has 1 triple bond = 2 DBE ✓

Key Concepts

🔍 Structure Determination

DBE narrows down possible structures from molecular formula

🧬 Spectroscopy Aid

Combined with NMR/IR to deduce molecular structure

⚗️ Aromatic Rings

DBE = 4 often indicates benzene ring (but not always!)

✅ Formula Validation

Negative or fractional DBE indicates an error in formula

Applications

  • 🔬
    Structure Elucidation: Determine possible structures from mass spectrometry data
  • 🧪
    Spectroscopy: Guide interpretation of NMR, IR, and UV-Vis spectra
  • 💊
    Drug Discovery: Analyze unknown compounds and metabolites
  • 🌿
    Natural Products: Characterize compounds isolated from plants and organisms
  • 📚
    Organic Chemistry Education: Problem-solving and structure drawing exercises
  • ⚖️
    Quality Control: Verify molecular formulas in pharmaceutical and chemical industries

🧬Quick Reference

Formula:

(2C + 2 + N - H - X) / 2

Each DBE =

1 ring OR 1 double bond
OR ½ triple bond

Ignored:

O, S (divalent atoms)

Common Value:

DBE = 4 often = benzene ring

Level:

College Organic Chemistry

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🎯Where It's Used

  • 🔬

    Analytical Chemistry

    Structure determination

  • 🧪

    Spectroscopy

    NMR/IR interpretation aid

  • 💊

    Pharmaceuticals

    Compound identification

  • 📚

    Education

    Organic chemistry problems