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I Standard Methods
There are many ways to convey information about organic molecules. Each method has advantages and disad- vantages to its use and many are situationally used. You should be familiar with all the methods used (especially Line Drawings). You should also be flexible in how you think about the molecules, and be able to shift from one form of drawing to another.
Below each section is a list of example molecules, they are the same for all sections, use them to see the similari- ties/differences and the advantages/disadvantages of each method.
Lewis Structures :
Lewis structures show the full structure of the molecule and include the lone pair electrons. Depending on the book/web-site bonds may be either shown as lines (like in class) or as electrons between two atoms (indicating they are shared).
Full Structural Formula:
Essentially the Lewis Dot structure of the molecule (minus lone pair electrons, see Ch 11 for review). It con- veys structural information in great detail and the class of the molecule is very apparent. It is also used often for chemical reactions because it conveys the complete structural information for the reaction mechanism. One disadvantages is size, it takes up multiple lines, thus only works well in figures (not normal text). The other disadvantage is it conveys a lot of information, that may not be needed, and can distract from the more important structural information. I rarely draw out full structural formula’s, there are alternative ways to convey the same information in a simpler and more concise manner, and I’m to lazy/efficient to draw them.
Ex: , ,
Molecular Formula:
Generally conveys the least amount of information as it contains no structural information, and does not even allow one to determine the class of the molecule. Generally used when the only information required is the number and type of atoms (for instance when calculating molecular weights) or to save space.
Ex: C 6 H 14 , C 3 H 6 O 3 , C 2 H 3 O 2
Condensed Structural Formula:
Contains some structural information, but no real details. It does allow the identification of the class of the molecule. Its main advantage is they information fits on one line of text (thus works well when using the formula in paragraphs). Disadvantages are they can be confusing for larger molecules.
Ex: CH 3 CHClCH 2 CH 2 CH 2 CH 3 , CH 3 COOH
To shorten the notation (and make it more readable) there are two conventions regarding the use of parenthesis. The first is to use parenthesis to indicate a group is repeated many times.
Ex: Condensed CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 vs With Parenthesis CH 3 (CH 2 ) 5 CH 3
The second convention is to use parenthesis to indicate side chains or functional groups in a molecule. The parenthesis show the group attached to the carbon to the left.
Ex: CH 3 CH 2 CH(CH 3 )CH 2 CH 3 is drawn
An excellent guide to condensed structures is linked at www.chemhaven.org/che102 from the web-site Mastering Organic Chemisry https://www.masterorganicchemistry.com/2011/06/20/deciphering-what-the-brackets-mean/
Hybrid Structures:
A compromise between condensed and full structural formula’s. Generally shows the full structure for the region of interest on the molecule and uses a condensed structure for the rest of the molecule. We will often use these in class when showing reaction mechanisms.
Ex: CH 3 CHCl(CH 2 ) 3 CH 3 or , ,
Naming Molecules:
Chemical names are designed to be unique for every possible chemical compound (there are billions). The rules were determined by the Union of Pure and Applied Chemists (IUPAC). The advantage to using chemical names is that they are often simple to represent, the major disadvantage is that they don’t make structural features obvious, and often it is harder to visualize how the reaction occurs.
Ex: 2-chlorohexane, 1,2,3-propanetriol, ethanoic acid
Ex # Molecular Condensed Structural Line
1 C 3 H 8 CH 3 CH 2 CH 3
CH 3 CH 2 CH 2 CH 2 CH 3
2 C 5 H 12 or
CH 3 (CH 2 ) 3 CH 3
CH 2 CHCH 2 CH 2 CH 3
3 C 5 H 10 or
CH 2 −−CHCH 2 CH 2 CH 3
CHCCH 2 CH 2 CH 3
4 C 5 H 8 or
CH−−−CCH 2 CH 2 CH 3
CH 3 CH(CH 3 )CH 2 CH 2 CH 3
5 C 6 H 14 or
CH 3 CH(CH 3 )(CH 2 ) 2 CH 3
CH 3 CHClCH 2 CH 2 CH 3
6 C 6 H 13 Cl or
CH 3 CHCl(CH 2 ) 2 CH 3
