Question

The general molecular formula for the homologous series of alkynes is C_nH_{2n - 2}. Write down the individual molecular formulae of the first, second and third members by substituting the values 2, 3 and 4 respectively for ‘n’ in this formula.

Answer 1

The general molecular formula for the homologous series of alkynes is C_nH_{2n - 2}

n = 2 C₂H_{2 × 2 – 2} = C₂H₂ Ethyne

n = 3 C₃H_{2 × 3 – 2} = C₃H₄ Propyne

n = 4 C₄H_{2 × 4 – 2} = C₄H₆ Butyne