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Chapter 8: Problem 158

Draw a Lewis structure for the \(N, N\) -dimethylformamide molecule. The skeletal structure is Various types of evidence lead to the conclusion that there is some double bond character to the \(\mathrm{C}-\mathrm{N}\) bond. Draw one of more resonance structures that support this observation.

Short Answer

Expert verified
The Lewis structure for N, N-dimethylformamide (DMF) has Carbon as the central atom, double bonded to Oxygen and single bonded to Nitrogen, with two Hydrogen atoms single bonded to Nitrogen. The total valence electrons are 18. Two resonance structures can be drawn for DMF, as shown below: Resonance structure 1: O // C=N / \ H H Resonance structure 2: O " || H-C-N / H These resonance structures show that there is some double bond character in the C-N bond, as supported by the evidence.

Step by step solution

01

Determine the total number of valence electrons

First, count the valence electrons for each atom in the molecule. Here, we have 1 Carbon (C), 1 Nitrogen (N), 1 Oxygen (O), and 4 Hydrogen (H) atoms. The number of valence electrons for each atom is: - Carbon (C): 4 - Nitrogen (N): 5 - Oxygen (O): 6 - Hydrogen (H): 1 Total valence electrons: 4(1 Carbon) + 5(1 Nitrogen) + 6(1 Oxygen) + 1(4 Hydrogens) = 18 valence electrons.
02

Determine the central atom and skeletal structure

Choose the least electronegative atom (excluding Hydrogen) as the central atom. In this case, Carbon is the least electronegative, so it will be the central atom. The skeletal structure given in the problem is O " || H-C-N / H
03

Arrange the other atoms around the central atom

Place the Oxygen atom double bonded to Carbon, Nitrogen atom single bonded to Carbon, and two Hydrogen atoms single bonded to Nitrogen as shown in the skeletal structure above. We have now used 10 of the 18 valence electrons.
04

Distribute electrons to satisfy the octet rule

Now, distribute the remaining 8 valence electrons to satisfy the octet rule around each atom (except Hydrogen, which follows the duet rule). However, since we have used all of the electrons, every atom in the molecule is already satisfying the octet (or duet) rule, and no further distribution is needed.
05

Modify the structure if any double or triple bonds are required

The current Lewis structure shows one double bond between Carbon and Oxygen atom and a single bond between Carbon and Nitrogen atoms. Since the evidence suggests that there is some double bond character to the C-N bond, we must draw resonance structures.
06

Draw resonance structures that support the double bond character to the C-N bond

Resonance structures are formed by moving electrons, not atoms. We can move one of the double bonds between Carbon and Oxygen to form a double bond with Nitrogen atom as shown below: Resonance structure 1: O // C=N / \ H H Resonance structure 2: O " || H-C-N / H The actual molecule is a hybrid of these resonance structures, suggesting a partial double bond character in the C-N bond.

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