Chemistry 400: General Chemistry
Discussion: Skeletal/Line-Bond Structures of Organic Molecules
The molecular structure of a carbon-based compound is not readily apparent by looking at a chemical formula. A chemical formula
can represent several different molecular structures. There are several types of molecular representations (Lewis structures, structural
formulas, dash-wedge structures, etc.) The Lewis structures and structural formulas for large carbon-based compounds are often
difficult to write.
Another type of structural representation, skeletal structures or line-bond structures, can be used to easily represent these molecules.
Biological molecules and pharmaceuticals are often partially represented as a skeletal structure. In a skeletal structure, no hydrogen
atoms are shown. It is assumed that in a skeletal structure any carbon will always have four bonds. If a carbon atom does not have four
bonds shown in the structure, the missing bonds are assumed to be to hydrogen atoms.
Some examples:
Chemical Formula
(a.k.a. Molecular Formula)
Lewis Structure/
Structural Formula
C 3H 8
propane
C4H10
butane
H
H
H
H
C
C
C
H
H
H
H
H
H
H
H
C
C
C
C
H
H
H
H
H
Skeletal / Line-Bond Structure
H
H
C 6H 6
benzene
H
H
C
C
C
C
H
C
C
H
H
O
H
C 7H 6O 2
benzoic acid
H
C
C
C
C
C
C
COOH
O
H
H
C
H
H
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1. Draw a skeletal structure for the following compounds. Also, build each molecule with the molecular modeling kits. Pay particular
attention to the angles and rigidity (or lack thereof) of a single and double bond bond.
CH3CH2CH2CH2CH2CH3
CH2=CHCH2CH3
CH3CHCH2CH2CH2CH3
|
CH3
CH3CHCH2CHCH3
|
|
OH
CH3
2. Draw the structural formula/Lewis structure for the following substances.
OH
3. One of the chemical components of DNA is cytosine (skeletal structure shown below).
A. Add lone pairs to the nitrogen and oxygen atoms.
B. What is the total number of lone pairs?
C. What is the molecular formula for cytosine?
NH2
N
O
N
H
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4. For the given line-bond structures, draw the corresponding structural formula/Lewis Structure, add lone pairs to the oxygen and
nitrogen atoms, and then determine the molecular formula for the compound and list the number of lone pairs.
Formula
Skeletal Line-Bond Structure
Structural Formula/Lewis Structure
(# LP)
2-amino-3-methyl benzyl alcohol
NH2
CH2OH
Droxidopa (antiparkinsonian)
OH
COOH
HO
NH2
HO
5. For each of the following formulas, draw the skeletal structure.
A. Fatty Acid: decanoic acid or capric acid
O H H H H H H H H H
H O C C C C C C C C C C H
H H H H H H H H H
B. Amino Acid: phenylalanine
H H
H H H N
H
C
C C C O H
C
C
H O
C
C
H
C
H
H
C. Hexadecane
CH3(CH2)14CH3
D. Heptadecane:
CH3(CH2)15CH3
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6. For each of the following molecules, draw the full Lewis structure structure.
A. Triglyceride: glycerol reacted with 3 long-chain fatty acids
O
H2 C O O
H2 C O
O
H2 C O
B. Phospholipid:
O
O
N
+
O
P O
O
O
O
O
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7. Structural isomers are molecules that have the same molecular formula but different bonding patterns of the atoms. Draw skeletal
structures of:
A. 3 structural isomers of C5H12
B. 5 structural isomers of C5H10 (different positions of the double bond are different molecules)
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