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Lewis Structuresof Organic Molecules
Dr. C. YauFall 2013
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Organic MoleculesOrganic chemistry is a study of compounds
containing carbon.In addition, they contain mostly H, O and
some N, S and P, and other elements.Those containing metals are said to be
“organometallic.”Hydrocarbons are compounds containing
only H and C.They are nonpolar because they contain onlyC-C and C-H bonds, which are nonpolar.
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Hydrocarbons
CH4
C2H6
C3H8
CH H
H
H
CH
H
H
C HH
H
CH
H
HC
C
H
HH
H
H
H C H
H
H
H C C C H
H
H
H
H
H
H
H C C H
H
H
H
H
Remember that C with 4 bonds is tetrahedral.
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Various Representations of Organic Molecules
Abbreviated
Line Drawings
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Isomers of Hydrocarbons
Beyond C3H8, there are isomers.
For example C5H12 has 3 isomers.
CH3CH2CH2CH2CH3
CH3CHCH2CH3
CH3
CH3CCH3
CH3
CH3
Classification of Organic Compounds
Organic compounds are classified by the “functional group” that replaces one or more of the H atoms in a hydrocarbon.Substitution of a H with –OH transforms it into an alcohol.For example, replacing one H with –OH in methane makes it methyl alcohol (or methanol).
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Alcohols
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H C H
H
HH C OH
H
H
C C H
H
H
H
H
HC C OH
H
H
H
H
H
methane methyl alcohol
ethane ethyl alcohol (in booze)
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Alcohols Contain -OH....but don’t call them hydroxides!!!Hydroxides are only for ionic cmpds.
They contain O-H and C-O bonds, which are polar.
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Carboxylic AcidsThese contain –COOH group or –CO2H
Learn this structure:
Formic acid HCOOH or HCO2H
CO
O H..:
: :
H CO
O H..:
: :
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MEMORIZE THIS!
Acetic acid CH3COOH or CH3CO2H
CO
O H
CH
H
H ..:
: :
Is it polar?
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Amines Contain N
CH3NH2
CH3CH2NH2
CH3NHCH3
CH3 NHH
CH3CH2 NHH
CH3 N HCH3
NH2
(CH3)2NH
..
..
..
They typically have an unpleasant odor, some with a fishy smell.
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Acetone (fingernail polish remover)
Acetone belongs in class called ketones.Memorize the structure of acetone.It is a very common organic solvent.CH3COCH3 or (CH3)2CO
CH3C CH3
O: :
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BenzeneBenzene is another very common organic
solvent.
What is its molecular formula?