Drawing Organic Structures• Organic compounds are held together by

covalent bonds

• a covalent bond may be represented by a pair of dots, or by a single line

Molecular formula

• Use methane as an example

• CH4

– molecular formula– shows relative numbers of atoms– conveys no sense of structure or bonding– conveys no sense of chemistry

Writing Molecular Formulas• The number of carbon atoms is specified first• The number of hydrogen atoms is specified next• The remaining atoms are then specified in (usually

alphabetical) order– cyclohexane: C6H12

– benzoic acid: C7H6O2

– ethyl para-aminobenzoate: C9H11NO2

– picryl chloride: C6H2ClN3O6

Full structural formula

• every atom specified• every bond explicitly shown

– methane is simple– two structures convey the same information

about as efficiently

C

H

H

HHC

H

H

H

H

Now lets try it with cholesterol as the example…

• Molecular formula– C27H46O

Full structural formula

C

C

C

C

C

C

C

C

C

C C

C

C

C

C

C

C

C

C

C

CC

CC

C

O

C

C

HH

HH

H H

HH

H H

H

H

HH

H H

HH

HH

H HH

H

H

H

H H

H HH

H

HH

H

H H H

HH

HH

H

HH

H

How do we simplify this?• recognize that every organic compound contains

carbon• delete the symbol for carbon atoms except for

those explicitly involved in a functional group (CHO, COOH, CN)

Lets do it…

O

HH

HH

H H

HH

H H

H

H

HH

H H

HH

HH

H HH

H

H

H

H H

H HH

H

HH

H

H H H

HH

HH

H

HH

H

Can we make it simpler…?• We have removed all the carbon symbols

(every organic compound contains carbon)

• Practically every carbon compound contains hydrogen– delete symbol for hydrogen except where it is

part of a functional group (e.g. CHO, OH)

Lets try that…

• Dramatic simplification– structural features are visible

• three rings

• length and shape of side chains

OH

Lets try that…

• Dramatic simplification– structural features are visible

– functional groups are visible• OH group of alcohol

• C=C double bond

OH

Lets try that…

• Dramatic simplification– structural features are visible – functional groups are visible– information is more available

• how long does it take to find the important features?

OH

The molecules of this experiment

• cyclohexane

– C6H12

• toluene

– C7H8

• benzoic acid

– C7H6O2

• ethyl para-aminobenzoate

– C9H11NO2

CH3

CO

O H

NH

H O

O C2H5

Properties

• all electrically neutral

• all soluble in non-polar solvents (e.g. ether)

• none soluble in water to an appreciable degree

• cyclohexane & toluene are liquids

• benzoic acid and ethyl para-aminobenzoate are solids

Benzoic acid

• a carboxylic acid

• has one acidic hydrogen– weak acid

– only slightly ionized

– pKa ≈ 4

• reacts with base to give benzoate anion and water

CO

O H

CO

O HC

O

O

+ H

CO

O HC

O

O

+ OH + H2O

• benzoic acid molecules are converted by strong base into benzoate anions

• benzoate anions are converted by strong acids into benzoic acid molecules

CO

O HC

O

O

OH

CO

O HC

O

O

H3O

A comparison• benzoic acid

– neutral, covalent molecules

– soluble in non-polar solvents (e.g. ether)

– almost insoluble in water

• sodium benzoate– sodium cations and

benzoate anions

– almost insoluble in non-polar organic solvents (e.g. ether)

– soluble in water

Ethyl para-aminobenzoate

• has both ester (neutral) and amine (base) functional groups

• has one basic nitrogen– weak base: gives practically no OH— in water

• reacts with acid to give alkylammonium cation

NH

H O

O C2H5

NH

H O

O C2H5

H3O

NH

H O

O C2H5

H

NH

H O

O C2H5

H

OH+ H2O +

+

NH

H O

O C2H5

• ethyl p-aminobenzoate molecules are converted by strong acid into alkylammonium cations

• the alkylammonium cations are converted by strong bases into ethyl p-aminobenzoate molecules

NH

H O

O C2H5

NH

H O

O C2H5

H

H3O

OH

NH

H O

O C2H5

H

NH

H O

O C2H5

A comparison• ethyl p-aminobenzoate

– neutral, covalent molecules

– soluble in non-polar solvents (e.g. ether)

– almost insoluble in water

• the alkylammonium salt– alkylammonium

cations and sulfate or chloride anions

– almost insoluble in non-polar organic solvents (e.g. ether)

– soluble in water