Answer to Question #129139 in Organic Chemistry for Hardy

Question

Determine the number of elements of unsaturation in the molecular formula C3H4. Give all three possible structures having this formula. Remember that
a double bond = one element of unsaturation
a ring = one element of unsaturation
a triple bond = two elements of unsaturation

Answer 1

The number of elements of unsaturation can be calculated by the formula: n + 1 - m/2, where n -- number of carbon atoms in one molecule, and m -- number of hydrogen atoms.

So, the number of elements of unsaturation in the molecular formula C3H4 is 3 + 1 - 4/2 = 2. Therefore, there should be either two double bonds, or a ring and a double bonds, or a triple bond in this molecule. Three possible structures are presented on this picture: