Textbook Question
Determine the degree of unsaturation and then draw possible structures for noncyclic compounds with the following molecular formulas:
a. C3H6
1. A Review of General Chemistry
Degrees of Unsaturation
3:11 minutesProblem 1a
Textbook Question
If a hydrocarbon has nine carbon atoms, three double bonds, and one ring, how many hydrogen atoms must it have?
Hint: If you prefer to use a formula, elements of unsaturation = 1/2(2C + 2 - H)
C = number of carbons
H = number of hydrogens
Verified step by step guidance1
Start by understanding the concept of elements of unsaturation. This concept helps determine the degree of unsaturation in a molecule, which includes rings and multiple bonds (double or triple bonds). Each ring or double bond counts as one element of unsaturation.
Identify the elements of unsaturation in the given hydrocarbon. The problem states there are three double bonds and one ring. Therefore, the total elements of unsaturation is 4.
Use the formula for elements of unsaturation: \( \text{Elements of Unsaturation} = \frac{1}{2}(2C + 2 - H) \). Substitute the known values: \( C = 9 \) and \( ext{Elements of Unsaturation} = 4 \).
Set up the equation based on the formula: \( 4 = \frac{1}{2}(2 \times 9 + 2 - H) \). Simplify the expression inside the parentheses: \( 2 \times 9 + 2 = 20 \).
Solve for \( H \) by isolating it in the equation: \( 4 = \frac{1}{2}(20 - H) \). Multiply both sides by 2 to eliminate the fraction: \( 8 = 20 - H \). Rearrange to find \( H \): \( H = 20 - 8 \).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydrocarbon Structure
Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon. The structure of a hydrocarbon can include chains, rings, and multiple bonds, which affect the number of hydrogen atoms present. Understanding the arrangement of carbon atoms and the presence of rings or double bonds is crucial for determining the molecular formula.
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Elements of Unsaturation
Elements of unsaturation refer to the presence of double bonds, triple bonds, or rings in a molecule, which reduce the number of hydrogen atoms compared to a saturated hydrocarbon. The formula 1/2(2C + 2 - H) calculates the degree of unsaturation, helping to determine the number of hydrogen atoms in a compound with given carbon atoms and unsaturation elements.
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Molecular Formula Calculation
To find the number of hydrogen atoms in a hydrocarbon, use the elements of unsaturation formula. For a hydrocarbon with nine carbon atoms, three double bonds, and one ring, calculate the unsaturation and adjust the hydrogen count accordingly. This involves understanding how each double bond and ring affects the hydrogen count compared to a fully saturated hydrocarbon.
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