An Introduction to Organic Chemistry

What is organic chemistry?

• The study of carbon-containing compounds• General properties are different from inorganic

compounds (e.g., ionic salts, etc.)• More than 5,000,000 known organic compounds

compared to only about 200,000 to 300,000 known inorganic compounds

• General properties are different from inorganic compounds (ionic salts etc.)

Comparison

Organic compounds Inorganic compounds

Covalent bonding Ionic bonding

Low melting points High melting points

Mainly insoluble in water Mainly soluble in water

Mainly soluble in organic solvents (e.g., gasoline)

Mainly insoluble in organic solvents

Almost all burn Very few burn

Slower reactions Very fast reactions

Covalent bonding

• A covalent bond involves sharing of a pair of electrons between two atoms

• Each atom contributes one electron for sharing• The shared electrons are localised between the two

atomic nuclei• Example

H● + H× H ● × HH ● × H can be represented as H—H

Why carbon?

• A carbon atom forms four bonds• Carbon atoms form stable bonds with other carbon

atoms (i.e., the C—C covalent bond is strong)• Can form chains and even networks • Examples: graphite and diamond• Carbon atoms also form stable bonds with other

atoms (i.e., C—H, C—O, C—N, C—Cl etc. bonds are strong)

• Many combinations and arrangements are possible

Hydrocarbons (CnHm)

• Extracted from crude oil• Separated according to size for various purposes• Source of energy, plastics, solvents, raw materials, etc.

Sucrose

C

C

C

O

C

C

OH

H

C

O

H H

H

OH

O

C

H

HO

C

C C

C

C

O

O

H H

O

OH H H

H

H

H

C12H22O11

Ethanol C2H5OH

C

H

H C

H

O

H

H

H

Aspirin (acetylsalicylic acid)

C

OH

O

OHC

O

OH

OCOCH3

(CH3CO2)O

H2SO4

Chlorofluorocarbons(CFCs)

C

F

ClCl

Cl

CFCl3

What are organic molecules?

• Main structure: carbon backbone• Each carbon must have 4 covalent bonds (i.e., share

an electron with a neighbouring atom)• Modular system, building blocks attached to each

other by covalent bonds• Functional groups with specific properties

Examples of functional groups

• Alkene C=C• Alcohol –OH• Halogen groups –Cl, –Br• Amine –NH2

• Carboxylic acid –COOH• Amide –CONH

Esters

Synthesised when a carboxylic acid and an alcohol react

R C

O

O H R O H

C O

O

R R H2O

Esters

• Responsible for many flavours and fragrances• E.g. banana flavour • Generally sweet and pleasant smells• Aspirin, an analgesic (painkiller)• Ethyl acetate, a solvent• Polyesters

Polyesters: applications

• Clothing (e.g., Dacron, terylene)• In sheet-form: tape• Used to make synthetic arteries for heart surgery• Absorbable staples for surgery

Racing Raisins

Apparatus/Chemicals

• one package of raisins

• a large beaker (800ml)

• carbonated water

• stop clock

Procedure

• Choose a raisin to drop into a large beaker of carbonated water

• Time how quickly the raisin sinks and rises back to the surface

• Race with each other!

• Observe the bubbles forming on the food surface during the experiment

• A raisin is denser than water it will initially sink

• Carbonated water contains carbon dioxide bubbles

• Rough surface creates a large surface area for the bubbles to attach to

• As the number of bubbles increases on the raisin, raisin and bubbles become less dense than water, hence rising to the surface

Science behind

• Once it has risen to the surface, the bubbles burst, releasing the carbon dioxide into the air

• Hence raisin sinks again

• Therefore, the items that work best will have a density that is only slightly greater than that of water

Science behind

SMOKE BOMB

Apparatus

• Hotplate• Satay Stick• Aluminum foil• Lighter• Mould• Wick• Lighter

Chemicals

• Potassium nitrate• Sugar (sucrose or table sugar)• Chemicals Used to Color Flames • Red - strontium salts• Orange - calcium chloride Yellow - sodium nitrate• Green - barium salts, such as barium nitrate

Procedure• Add sugar to potassium nitrate in the ratio of 2:3

on a piece of aluminum foil.• Add chemical that colour the flame, sparingly.• Heat the mixture on a hotplate on low heat.• Stir the mixture well using a satay stick.• When the mixture turned brown, take it off the

heat and wrap the mixture with that aluminum foil.

• When it has hardened – takes about 10minutes – light it up and coloured flames will be produced.

Chemistry Behind

• Sugar – fuel• Potassium nitrate- oxidizer • Salt- organic dye • 48NaNO3 + 5C12H22O11 - 60CO2 + 55H2O + 24N2 +

24Na2O

• A simple test to determine the pH of household solution – acidic or basic?

Red cabbage indicator

Apparatus/Chemicals• red cabbage • blender or knife • filter paper • one large glass beaker• glass rod • Heater• lemon juice • vinegar • milk• seven up• coffee • baking soda • household bleach• masonry's cleaner

Procedure

• Chop the cabbage into small pieces. • Place the cabbage in a large beaker and add water to

cover the cabbage. Allow at least ten minutes for the color to leach out of the cabbage.

• Filter out the plant material to obtain a red-purple-bluish colored liquid. This liquid is at about pH 7.

• Soak a filter paper in this liquid. Allow it to dry. Cut the dry colored paper into test strips.

• Use a dropper or toothpick to apply a little liquid to a test strip.

• Compare the colour change

pH 2 4 6 8 10 12

colour red purple violet blue Blue-green

Greenish yellow

Material Color of filter paper Acidic or basic

pH

baking soda

lemon juice

milk

.

.

.

-

acidic neutral basic

Chemistry behind

• Red cabbage contains a pigment molecule called flavin (an anthocyanin)

• This water-soluble pigment is also found in apple skin, plums, poppies, cornflowers, and grapes.

- The color of the juice changes in response to changes in its hydrogen ion concentration.

- Acids will donate hydrogen ions in an aqueous solution and have a low pH (pH < 7).

- Bases accept hydrogen ions and have a high pH (pH > 7).

• A solution whose pH is 7 is said to be neutral, that is, it is neither acidic nor basic. Water is subject to a self-ionisation process.– H2O H+ + OH−

• pH indicators are frequently employed in titrations in analytic chemistry and biology experiments to determine the extent of a chemical reaction.

• Common pH indicators in lab: – Phenolphthalein– methyl orange – methyl green

What is pH?

Cornflour Slime

Apparatus/Chemicals

• A big beaker• Cornflour• Water

Procedure

1. Put the cornflour in the bowl and while stirring, add water a little at a time until all the cornflour is wet.

2. Keep adding water, a little by little, and stirring until a thick slime forms. Be careful not to add too much water.

3. Make a fist and punch the surface of the slime - the slime will feel hard.

4. Do the same thing, but very slowly and your hand will emerge from the bowl covered in wet, sloppy slime.

Science behind

• Cornflour slime is a stir thickening (dilatant) fluid. • Most fluids are ‘Newtonian’ and their viscosity

(runniness) stays the same, whether or not they are being stirred.

• Cornflour slime is a non-Newtonian fluid. It becomes thicker (more viscous) when stirred (a shear force is applied; punching it works as well).

• The slime returns to its runnier (less viscous) state when the force is removed.