Q.What are alkenes? Calculate the number of sigma (s) and pi (p) bonds in 2-Methylpropene. Write structural formula of pent-2-ene.

Step 1. Define alkenes. Alkenes are unsaturated aliphatic hydrocarbons containing at least one carbon-carbon double bond, general formula CnH2n (section 15.2).

Step 2. Count bonds in 2-methylpropene. 2-Methylpropene is (CH3)2C=CH2, molecular formula C4H8. Listing every bond: the C=C itself contributes 1 sigma + 1 pi; the central carbon's two C-CH3 bonds are 2 sigma; the terminal =CH2 carbon's two C-H bonds are 2 sigma; the two CH3 groups contribute 3 C-H sigma bonds each, 6 sigma in total. Adding the sigma bonds: 1 (C=C sigma) + 2 (C-CH3) + 2 (=CH2's C-H) + 6 (two CH3's C-H) = 11 sigma bonds, plus the 1 pi bond of the do …

Recalling the alkene definition, then a direct bond-by-bond count for the sigma/pi total, then applying …

• Forgetting that the C=C itself contributes ONE sigma bond in addition to its one pi bond -- undercounting sigma bonds by treating the double bond as pure pi. …