MOLECULAR POLARITY
Covalent Compounds  Elmhurst College
Electrostatic Potential Organic Functional Groups Functional Gps vs. Boiling Pt.  Chemistry Department
Simple Inorganics Organic Chain Length  Virtual ChemBook


Polarity of Organic Compounds

Principles of Polarity:

The greater the electronegativity difference between atoms in a bond, the more polar the bond. Partial negative charges are found on the most electronegative atoms, the others are partially positive.

The molecular electrostatic potential is the potential energy of a proton at a particular location near a molecule.
Negative electrostatic potential corresponds to:
partial negative charges (colored in shades of red).
Positive electrostatic potential corresponds to:
partial positive charges (colored in shades of blue).


 

Comments on the Electrostatic Potential graphics below:

As you view the graphics, the idea is to develop the concept of polarity in a visual manner.

The more areas of red and blue that you see, the more polar is the compound and the functional group in the compound. Look at the amide, and acid.

The more areas of gray and lighter shades of red and blue, the more non-polar properties are being depicted. Look at the amine, ether, and alkane.

A strong exception based on the above statements is that the ester should have a much higher ranking than it does based upon the boiling point information. Other factors may also be important.

 

Functional Group Ranking by Boiling Points
 

R = any number carbons in a hydrocarbon chain
*CHIME plug-in required to view these images.
 

Functional
Group
Name

 Boiling
Point

 Polar
Rank
(most
to
least)

 Structure

Name

 Name

Chime*
 

Amide

222o

 1

 

 ethanamide

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 Acid

118o

 2

 

ethanoic acid
or
acetic acid

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 Alcohol

117o

 3

 CH3CH2CH2OH

 propanol

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Ketone

56o

 4, 5

propanone
or
acetone

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Aldehyde

49o

 4, 5

 propanal

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Amine

49o

 6

CH3CH2CH2NH2

propylamine

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 Ester

32o

 7

methyl
ethanoate

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 Ether

  11o

 8

 CH3-O-CH2CH3

 methyl ethyl ether

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 Alkane 

-42o

 9

 CH3CH2CH3

propane

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