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 CH 4 –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: C 6 H 12 –benzoic acid: C 7 H 6 O 2 –ethyl para-aminobenzoate: C 9 H 11 NO 2 –picryl chloride: C 6 H 2 ClN 3 O 6

Full structural formula every atom specified every bond explicitly shown –methane is simple –two structures convey the same information about as efficiently

Now lets try it with cholesterol as the example… Molecular formula –C 27 H 46 O

Full structural formula

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…

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

Lets try that… Dramatic simplification –structural features are visible –functional groups are visible OH group of alcohol C=C double bond

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?

The molecules of this experiment cyclohexane –C 6 H 12 toluene –C 7 H 8 benzoic acid –C 7 H 6 O 2 ethyl para-aminobenzoate –C 9 H 11 NO 2

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 –pK a ≈ 4 reacts with base to give benzoate anion and water

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

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

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

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