Methyl isocyanate, \(\mathrm{CH}_{3}-\mathrm{N}=\mathrm{C}=\mathrm{O}\), is used in the industrial synthesis of a type of pesticide and herbicide known as a carbamate. As a historical note, an industrial accident in Bhopal, India, in 1984 resulted in leakage of an unknown quantity of this chemical into the air. An estimated 200,000 persons were exposed to its vapors, and over 2000 of these people died. (a) Write a Lewis structure for methyl isocyanate, and predict its bond angles. What is the hybridization of its carbonyl carbon? Of its nitrogen atom? (b) Methyl isocyanate reacts with strong acids, such as sulfuric acid, to form a cation. Will this molecule undergo protonation more readily on its oxygen or nitrogen atom? In considering contributing structures to each hybrid, do not consider structures in which more than one atom has an incomplete octet.

Step by step solution

01

Drawing the Lewis Structure

To draw the Lewis structure, we first need to count the total number of valence electrons present in the molecule. For methyl isocyanate, we have: Carbon (C) has 4 valence electrons Hydrogen (H) has 1 valence electron Nitrogen (N) has 5 valence electrons Oxygen (O) has 6 valence electrons So, the total number of valence electrons in methyl isocyanate is (4+3+5+6) = 18. Next, we need to arrange the atoms and connect them with single bonds. The central atom can be the nitrogen atom, and the other atoms (CH3, carbon, and oxygen) are connected to it. The molecule should look like: CH3-N=C=O. Now we need to distribute the remaining valence electrons as lone pairs. The oxygen atom will have two lone pairs.

02

Predicting Bond Angles

According to VSEPR theory, the arrangement around the nitrogen atom will be trigonal planar. The bond angles between the C-N and N=C should be around 120°. The arrangement around the carbonyl carbon will be linear, with bond angles of 180°.

03

Identifying the hybridization of carbonyl carbon and nitrogen atom

To find the hybridization, we can use the concept of steric number (SN). The steric number can be calculated using the formula: SN = Number of sigma bonds + Number of lone pairs. For the carbonyl carbon atom, it forms two sigma bonds (C=N and C=O) and has no lone pairs. Thus, SN = 2. Therefore, the hybridization of the carbonyl carbon is sp. For the nitrogen atom, it forms two sigma bonds (N=C and N-CH3) and has one lone pair. Thus, SN = 3. Therefore, the hybridization of nitrogen atom is sp2. (b)

04

Analyzing the protonation on oxygen or nitrogen atom

When a molecule reacts with a strong acid, it gains a proton (H+). In the case of methyl isocyanate, both oxygen and nitrogen atoms have lone pairs, so both can potentially accept protons from strong acids. We need to find out which one is more likely to get protonated. Generally, the more electronegative atom (which tends to hold electrons more tightly) is less likely to accept a proton. Between nitrogen and oxygen, the oxygen atom is more electronegative. Therefore, the nitrogen atom will be more likely to accept a proton from a strong acid. Hence, methyl isocyanate will undergo protonation more readily on its nitrogen atom.

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