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Lewis Structuresof Organic Molecules

Dr. C. Yau

Fall 2011

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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 nonpolar because they contain only

C-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

H

H C OH

H

H

C C H

H

H

H

H

H

C 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!!!

They contain O-H and C-O bonds, which are polar.

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Carboxylic Acids

These contain –COOH group or –CO2H

Learn this structure:

Formic acid HCOOH or HCO2H

C

O

O H..:

: :

H C

O

O H..:

: :

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MEMORIZE THIS!

Acetic acid CH3COOH or CH3CO2H

C

O

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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Benzene

Benzene is another very common organic solvent.

What is its molecular formula?