How many elements of unsaturation are implied by the molecular formula C₅H₈O?

Question

Quizplus · Accepted Answer

To calculate elements of unsaturation, we use the formula: [(2C + 2 + N - X - H)/2], where C = number of carbons, N = number of nitrogens, X = number of halogens (halogens are Cl, Br, and I). H = number of hydrogens. In this case, we have 1 carbon, 1 sulfur, 1 oxygen, and a total of 35 hydrogens. Plugging these values into the formula, we get [(2(1) + 2 + 0 - 0 - 35)/2] = -16.5, which we round to -17. Since we can't have a negative number of elements of unsaturation, we change the sign and get an answer of 17. Therefore, there are 17 elements of unsaturation, which is equivalent to 2 double bonds and 1 ring (or 2 rings, depending on how the molecule is drawn). Choice C (2) is the correct answer.

How Many Elements of Unsaturation Are Implied by the Molecular