A simple procedure for writing Lewis structures is given in a previous
article entitled “Lewis
Structures and the Octet Rule”.
Several worked examples relevant to this procedure were given in previous posts please see the Sitemap - Table of Contents (Lewis Electron Dot Structures).
Let us consider the case of methyl acetate, CH3COOCH3
Methyl acetate is a flammable liquid with a characteristic pleasant smell reminiscent of some glues and nail polish removers. It is used as a weakly polar and lipophilic solvent. Because of its fast evaporation rate is useful in applications where fast solvent release and quick-dry to touch time is required. Methyl acetate is the active solvent for several resins.
Step 1: Connect the atoms of CH3COOCH3 with single bonds
Fig. 1: Connecting the atoms of CH3COOCH3 with single bonds
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Step 2: Calculate the # of
electrons in π bonds (multiple bonds) using formula (1):
Where n in this
case is 5 since CH3COOCH3 consists of 11 atoms but 6 of them are H
atoms.
Where V = 4 +
3*1 + 4 + 6 + 6 + 4 +3*1 = 30
Therefore, P = 6n
+ 2 – V = 6 *5 + 2 – 30 = 2 So there is one double bond and that means the
structure in Step 1 has one double bond.
Step 3 & 4: The Lewis structure of CH3COOCH3 is as follows:
Fig. 2: Lewis
electron dot structures for methyl acetate CH3COOCH3
.
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Lewis electron dot structure #1 is the major contributor to the hybrid since there are 8
electrons around each atom and there is no charge separation (extra stability).
Structure #2 is the least plausible contributor because there is charge
separation and positive charge on an electronegative atom (O atom)
(unstable). Structure #3 is a minor contributor since there is charge
separation but the positive charge is on the most electropositive atom (C atom)
comparing to the others connected.
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