A Lewis structure for NCS is shown below, however, its formal charges are not minimized

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A Lewis structure for NCS is shown below, however, its formal charges are not minimized. Starting from this structure, complete the correct structure with minimized formal charges.

2,2,2-trifluoroethanol, CF3CH2OH. is used industrially as a solvent for nylon. Draw the Lewis structure of CF3CH2OH. In your final structure, please make sure the elements are in the order they are provided.

The Correct Answer and Explanation is :

Let’s break down both parts of your question step by step.

Part 1: Lewis Structure of NCS (Isothiocyanate)

The structure for NCS (which stands for the isothiocyanate group, where N is nitrogen, C is carbon, and S is sulfur) is as follows:

  1. Start with the basic structure: N—C—S, where nitrogen is connected to carbon, and carbon is connected to sulfur.
  2. Nitrogen can have a lone pair, carbon will likely need two bonds to achieve stability, and sulfur will have lone pairs as well.
  3. Assign formal charges: We want to minimize formal charges, so follow these steps:
  • Nitrogen typically has 5 valence electrons, carbon 4, and sulfur 6.
  • If nitrogen forms a single bond with carbon and carbon forms a triple bond with sulfur, the formal charge distribution can be minimized.
  1. The final structure is: N=C=S, where:
  • Nitrogen has no formal charge (0).
  • Carbon has no formal charge (0).
  • Sulfur has no formal charge (0).

In this structure, the formal charges are minimized, with each atom having a stable electron configuration.

Part 2: Lewis Structure of 2,2,2-Trifluoroethanol (CF3CH2OH)

Now, let’s look at the Lewis structure for 2,2,2-trifluoroethanol (CF3CH2OH), which consists of:

  • A trifluoromethyl group (CF3) attached to an ethanol group (CH2OH).
  1. Start by drawing the backbone: CH2—CH2—OH.
  2. Attach the trifluoromethyl group (CF3) to the second carbon (C2).
  3. Next, we distribute the electrons:
  • The trifluoromethyl group (CF3) has three fluorine atoms each forming a single bond with carbon. Each fluorine atom will have three lone pairs.
  • The second carbon (C2) will have a single bond to both the trifluoromethyl group (CF3) and the first carbon (C1).
  • The first carbon (C1) will form a single bond with two hydrogen atoms.
  • The oxygen in the hydroxyl group (OH) will be single-bonded to the second carbon (C2), and the hydrogen attached to oxygen will complete the structure.
  1. Now, check the formal charges:
  • Carbon atoms in this structure should have no formal charge (0).
  • Oxygen in the hydroxyl group typically has no formal charge (0).
  • Fluorine atoms will each have no formal charge as well, since fluorine has 7 valence electrons and forms one bond in CF3.

The final structure for CF3CH2OH is:

   F   F   F
    |   |   |
H3C—C—OH
  • Carbon 1 (C1) is bonded to two hydrogens (CH2).
  • Carbon 2 (C2) is bonded to the trifluoromethyl group (CF3) and the hydroxyl group (OH).
  • Fluorines are attached to carbon 2.
  • Oxygen is attached to carbon 2 and has a single bond to hydrogen.

This completes the Lewis structure for 2,2,2-trifluoroethanol with minimized formal charges.

Explanation:

In both structures:

  1. Formal charges are calculated by comparing the number of valence electrons each atom has in the molecule with how many it “owns” after bonding (considering lone pairs and shared electrons).
  2. Minimizing formal charges usually means that atoms in the molecule are as close as possible to their preferred electron configurations (e.g., carbon prefers 4 bonds, oxygen prefers 2 bonds and 2 lone pairs, fluorine prefers 1 bond and 3 lone pairs).

In both cases, the structures are designed to minimize formal charges while adhering to the bonding patterns that make sense for each atom’s valence electrons.

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