Lewis Structures: Drinking Alcohol and Isomers

Video by Janet Gray Coonce, MS

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Next to draw the Lewis dot structure for ethanol, the alcohol which is found in fermented beverages.  Fermentation is the organic chemical reaction whereby yeast metabolize sugars which are found in fruits to ethanol and carbon dioxide.  The molecular formula for ethanol is C₂H₆O.  There would be 2 ways of writing the Lewis structural formula C₂H₆O.  When compounds have the same molecular formula but different structural formulas they are referred to as isomers.  We want to draw the Lewis dot structure for ethanol.

Another way of writing the molecular formula for ethanol helps to illustrate exactly which isomer we are referring to and how we should draw the Lewis dot structure.  Writing the formula as CH₃CH₂OH indicates we are specific that we are referring to the isomer of C₂H₆O which is ethanol.

By writing the formula in this way we know that there is a CH₃ group, a CH₂ group and an OH group.   Writing the formula in this way (CH₃–CH₂ –OH) tells us which of the structural formulas we are referring to and how to draw the Lewis dot structure.

When we draw the Lewis dot structure, we first write the central atoms.  Remember hydrogens always go on the outside.  We start with the CH₃ group, then CH₂, then OH.  Next step is to place dots for the valence electrons.  Hydrogen gets 1, carbon gets 4 and oxygen gets 6.  The lone electron is available for bonding.

The Lewis structure is complete when we connect the dots to show the sharing of electron pairs between different atoms.

Here is the Lewis dot structure for the other isomer of C₂H₆O, dimethyl ether.  Another way of writing this molecular formula is CH₃-O-CH₃.

Here is the Lewis dot structure for dimethyl ether.  Although it has the same molecular formula as ethanol, it is a different compound with different physical properties because of the different way the atoms are arranged.  Dimethyl ether is a gas, not a liquid.  Dimethyl ether is used as a refrigerant and is used to freeze warts much the same way as liquid nitrogen.  It is not something anyone would want to attempt to drink.  It is an isomer of C₂H₆O which is the same molecular formula as ethanol.

Transcription by James C. Gray MD FACOG