Textbook Question
Calculate the number of elements of unsaturation implied by the molecular formula C6H12.
Hint: If you prefer to use a formula, elements of unsaturation = 1/2(2C + 2 - H)
C = number of carbons
H = number of hydrogens
1. A Review of General Chemistry
Degrees of Unsaturation
Problem 6a
Textbook Question
Given the structure, calculate the index of hydrogen deficiency (degrees of unsaturation) of the following molecules.
(a) 
Verified step by step guidance1
Step 1: Understand the formula for calculating the Index of Hydrogen Deficiency (IHD). The formula is: IHD = (2C + 2 + N - H - X) / 2, where C = number of carbons, H = number of hydrogens, N = number of nitrogens, and X = number of halogens (e.g., F, Cl, Br, I). Oxygen atoms do not affect the calculation.
Step 2: Identify the molecular formula of the given structure. Count the number of carbons (C), hydrogens (H), nitrogens (N), and halogens (X) in the molecule.
Step 3: Substitute the values of C, H, N, and X into the IHD formula. Ensure that you perform the arithmetic operations carefully.
Step 4: Interpret the result of the IHD calculation. Each unit of IHD corresponds to one degree of unsaturation, which could represent a double bond, a ring, or a triple bond (which counts as two degrees).
Step 5: Verify your result by analyzing the structure of the molecule. Check for the presence of double bonds, triple bonds, or rings to confirm the calculated IHD matches the structural features.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Index of Hydrogen Deficiency (IHD)
The Index of Hydrogen Deficiency (IHD), also known as degrees of unsaturation, indicates the number of rings and/or multiple bonds in a molecule. It is calculated using the formula IHD = (2C + 2 + N - H - X) / 2, where C is the number of carbons, N is the number of nitrogens, H is the number of hydrogens, and X is the number of halogens. A higher IHD suggests more unsaturation, which can affect the molecule's reactivity and stability.
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Molecular Structure
Understanding the molecular structure is crucial for calculating IHD, as it involves identifying the number of carbon, hydrogen, nitrogen, and halogen atoms present. The arrangement of these atoms, including any functional groups or rings, directly influences the degree of unsaturation. A clear representation of the molecular structure, such as a Lewis structure or skeletal formula, helps in visualizing and counting the relevant atoms.
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Functional Groups
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Recognizing functional groups is essential when calculating IHD, as they can contribute to the overall unsaturation of the molecule. For example, double bonds and rings increase the IHD, while single bonds do not, making it important to identify these features in the molecular structure.
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