Question

Question: Stalevo is the trade name for a medication used in Parkinson’s disease, containing L-dopa, carbidopa, and entacapone.

a. Draw a Lewis structure for entacapone.

b. Which C–C bond in entacapone is the longest?

c. Which C–C single bond is the shortest?

d. Which C–N bond is the longest?

e. Which C–N bond is the shortest?

f. Use curved arrows to draw a resonance structure that is an equal contributor to the resonance hybrid.

g. Use curved arrows to draw a resonance structure that is a minor contributor to the resonance hybrid.

Short answer

Answer

1. 
2. The C-C bond involving ${\mathrm{sp}}^3$ -hybridized carbon atoms is the longest.
3. TheC-C bond involvingthe carbon atom having the maximum s character will be the shortest.
4. The C-N single bond will be the longest.
5. The $\mathrm{C}\equiv \mathrm{N}$ will be the shortest.
6. 
7. 

Step-by-step solution

 Step-by-Step Solution Step 1: Lewis structures

Lewis structures are used to describe the bonding in a molecule.

The Lewis structure of the entacapone molecule is as follows:

Lewis structure of entacapone

Bond length

The distance between the centers/nuclei of two chemically bonded atoms is termed the bond length.

The C-C bond length decreases as the s character of the carbon atom increases.

The C-C bonds formed by${\mathrm{sp}}^3$-hybridized carbon atoms are the longest.

The C-N bond involving a ${\mathrm{sp}}^3$ -hybridized carbon will be the longest, and the shortest will be the one that involves an sp-hybridized carbon atom or the one that has the maximum s character.

Representation of C-C and C-N bond in entacapone

Resonance structures of entacapone

The combination of Lewis structures used to describe the bonding in molecules is named the resonance structures.

The molecule entacapone has two resonance structures that are an equal contributor to the resonance hybrid.

Resonance structures of entacapone

The molecule entacapone also has two minor resonance contributors that describe the bonding of the amide group present as a substituent on the aromatic ring.

Resonance structures of entacapone