Video Transcript
How many 𝜎 bonds and 𝜋 bonds are
in 1,3-pentadiene, H2C double bond CH single bond CH double bond CH single bond
CH3? (A) 12 𝜎 bonds and two 𝜋 bonds,
(B) 10 𝜎 bonds and two 𝜋 bonds, (C) two 𝜎 bonds and 12 𝜋 bonds, or (D) two 𝜎
bonds and 10 𝜋 bonds.
𝜎 bonds are covalent bonds that
are formed through the head-on or end-to-end overlap of different types of
hybridized or unhybridized bonding orbitals. 𝜋 bonds are a type of covalent
bond that are formed through the sideways overlap of two adjacent p-subshell
orbitals.
Let’s look at a molecule of ethene
to see this more clearly. In a carbon–carbon double bond, the
carbon atoms will be sp hybridized. Each carbon atom will have three sp
orbitals. Two of the orbitals overlap to form
a carbon–carbon 𝜎 bond. Four other 𝜎 bonds form between
the carbon atoms and hydrogen atoms. A 𝜋 bond forms between the carbon
2p orbitals. It is now clear that a single bond
is a 𝜎 bond and a double bond contains a 𝜎 and 𝜋 bond.
Let’s now redraw
1,3-pentadiene. To make it easier to determine the
amount of 𝜎 bonds and 𝜋 bonds in 1,3-pentadiene, we can say that all the
carbon–carbon single bonds and carbon–hydrogen bonds are 𝜎 bonds. The carbon–carbon double bonds are
made up of one 𝜎 bond and one 𝜋 bond. It is clear that there are two 𝜋
bonds in total. Therefore, neither option (C) or
(D) can be correct. If we count up the number of 𝜎
bonds, we find that there are 12.
Therefore, the number of 𝜎 and 𝜋
bonds in 1,3-pentadiene is (A), 12 𝜎 bonds and two 𝜋 bonds.
