Organic Chemistry MCAT Practice Exam

The degree of unsaturation, also known as the index of hydrogen deficiency (IHD), is a crucial concept in organic chemistry that helps determine the number of π bonds and rings within a molecular structure. To derive this, one should consider the tetravalency of carbon, which means a carbon atom can form four bonds. The correct formula for calculating the degree of unsaturation is given as \( U = \frac{(2C - H + N + 2)}{2} \). In this formula: - \( C \) represents the number of carbon atoms in the molecular formula. - \( H \) is the number of hydrogen atoms. - \( N \) accounts for nitrogen atoms (since nitrogen can make three bonds and contributes to unsaturation). - The constants in the formula account for the hydrogens that would be present if the compound were fully saturated (aliphatic). This formula effectively calculates how many hydrogen atoms are "missing" from what would be expected for a saturated compound. Each degree of unsaturation corresponds to either one ring or one π bond. By using this formula, one can quickly establish the structural characteristics of an organic molecule, making it a vital tool in organic chemistry. To clarify why other choices do