Show the σ (sigma) and π (pi) bonds present in the following molecules: C6H6, C6H12, CH2Cl2, CH2=C=CH2

**OR**

Write the IUPAC names of the following: (a) [structural formula: CH3-C(=O)-CH3, drawn with the C=O bond shown vertically below the central carbon] (b) [structural formu

Question

Show the σ (sigma) and π (pi) bonds present in the following molecules: C6H6, C6H12, CH2Cl2, CH2=C=CH2

**OR**

Write the IUPAC names of the following: (a) [structural formula: CH3-C(=O)-CH3, drawn with the C=O bond shown vertically below the central carbon] (b) [structural formula: a six-membered ring bearing a -Cl substituent (bond from the upper area) and an -OH substituent (bond from the lower-right)]

Accepted Answer

>

> [!TLDR]
> Answering the primary part of this OR question: counting each molecule's sigma and pi bonds gives C6H6 = 12σ+3π, C6H12 = 18σ+0π, CH2Cl2 = 4σ+0π, and CH2=C=CH2 = 6σ+2π. (The OR alternative asked for IUPAC names from a hand-drawn figure; see the note on that below.)
>
> Rule used throughout: every single bond is 1 sigma bond; every double bond is 1 sigma + 1 pi bond; every C-H bond is a sigma bond.
>
> 1. C6H6 (benzene, planar 6-membered ring with alternating double bonds in the Kekulé structure): 6 C-C sigma bonds forming the ring + 6 C-H sigma bonds (one per carbon) = 12 sigma bonds. The ring's 3 formal C=C double bonds contribute 3 pi bonds (these are actually delocalised over the ring, but the bond count is still 3 pi bonds' worth of electron density).
> Total: 12σ, 3π.
>
> 2. C6H12 (cyclohexane, saturated 6-membered ring, all single bonds): 6 C-C sigma bonds (ring) + 12 C-H sigma bonds (2 H per carbon × 6 carbons) = 18 sigma bonds, and no pi bonds since the ring is fully saturated.
> Total: 18σ, 0π.
>
> 3. CH2Cl2 (dichloromethane, a single sp3 carbon bonded to 2 H and 2 Cl): 2 C-H sigma bonds + 2 C-Cl sigma bonds = 4 sigma bonds total, and no pi bonds (no multiple bonds present).
> Total: 4σ, 0π.
> …

Q.Show the σ (sigma) and π (pi) bonds present in the following molecules: C6H6, C6H12, CH2Cl2, CH2=C=CH2 OR Write the IUPAC names of the following:

Concept understanding — Sigma Pi Bond Counting

Sigma Pi Bond Counting: From Intuition to Precision

Why sigma comes first

The precise counting method

A worked example: ethene ( $\ce{C2H4}$ )

A trickier case: benzene ( $\ce{C6H6}$ )

Q.Show the σ (sigma) and π (pi) bonds present in the following molecules: C6H6, C6H12, CH2Cl2, CH2=C=CH2 OR Write the IUPAC names of the following:

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