In each of the following compounds, the C atoms form a single ring. Draw a Lewis structure for e

step 1 Okay, so starting with Part A, we have C3H4. So we can start by drawing three carbons in a ring.

In each of the following compounds, the C atoms form a...

In each of the following compounds, the $\mathrm{C}$ atoms form a single ring. Draw a Lewis structure for each molecule, identify cases for which resonance exists, and determine the carbon-carbon bond order(s): (a) $\mathrm{C}_{3} \mathrm{H}_{4} ;$ (b) $\mathrm{C}_{3} \mathrm{H}_{6} ;$ (c) $\mathrm{C}_{4} \mathrm{H}_{6} ;$ (d) $\mathrm{C}_{4} \mathrm{H}_{4} ;$ (e) $\mathrm{C}_{6} \mathrm{H}_{6}$.

Key Concepts

Lewis Structures

Lewis structures are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist. They provide a basic representation of a molecule’s connectivity and electron arrangement, serving as the foundation for determining molecular geometry and predicting reactivity patterns.

Resonance

Resonance refers to the situation where more than one valid Lewis structure can represent a molecule’s electron distribution. In cases of resonance, the actual electron distribution is a hybrid of these structures, which can lead to delocalization of electrons and affect molecular stability, reactivity, and bond characteristics such as bond order.

Carbon-Carbon Bond Order

The bond order between two carbon atoms is defined as the number of chemical bonds (or the effective bond strength) shared between them. In compounds exhibiting resonance or alternating single and double bonds in a cyclic framework, the bond order may be fractional, reflecting the delocalized nature of electrons within the cycle.

Cyclic Compounds

Cyclic compounds, or ring structures, consist of atoms connected in a closed loop. Their unique ring geometry influences electronic structure and reactivity, often involving concepts such as ring strain, aromaticity, and conjugation, which can have significant impacts on bond lengths and bond orders.

Transcript

00:01 Okay, so starting with part a, we have c3h4.

00:03 So we can start by drawing three carbons in a ring.

00:07 And in order for there to be four hydrogens, we need to have one carbon -carbon double bond, so that each of these carbons down here is attached to one hydrogen.

00:17 And the carbon that has no double bonds is attached to two hydrogens.

00:23 So this will have two other resonance forms, where the carbon -carbon double bond will be in a different place.

00:28 Instead of at the bottom here, it's going to be to the left, and then we'll draw in that four hydrogens here, here, and here.

00:36 And the last resonance structure will have the carbon -carbon double bond over to the right, and then draw in those hydrogens.

00:48 So there's three resonance forms for part a.

00:51 And the bond order, we have four carbon -carbon bonds, one, two, three, four in each of these residence forms, and there's three carbons, so the bond order is going to be 4 over 3.

01:04 Moving on to part b, we have c3h6.

01:08 So start by drawing the three carbon ring, and each of those carbons can be bound to two hydrogens.

01:18 And that uses up six.

01:20 There's no double or triple bonds within the ring, so part b has no resonance forms.

01:27 And the bond order is just 3 over 3 or 1.

01:32 Moving on to part c, we have c4h6.

01:37 So we'll draw the four carbons in a square like this.

01:42 And one of those carbon -carbon bonds is a double bond.

01:46 So now we can draw in the hydrogen.

01:47 So there's one, two, three, four, five, six.

01:53 And all the resonance forms, i'm not going to draw in the hydrogens, but that location of that carbon -carbon double bond will change.

02:02 So it's at the top here...