Orgnic Chemistry

Organic Chemistry Class 401 / 404

Important terms you should know:
1. addition reaction (TB pg 425)
Reaction in which a molecule (element or compound) adds to an unsaturated compound to form a single new compound (referred only to alkenes).

2. cracking (TB pg 428)
The breaking down of long chain hydrocarbon molecules with heat and/or catalyst to produce smaller hydrocarbon molecules or hydrogen.

3. fermentation (TB pg 436)
The conversion of glucose (or simple sugars) by yeast into carbon dioxide and ethanol.

4. functional group (TB pg 416)
An atom or group of atoms that gives characteristic properties to an organic compound.

5. homologous series (TB pg 418)
Family of organic compounds with same general formula (same functional group), having similar chemical properties, showing slight gradation in the physical properties, and having each member differ from the next by a –CH2 unit.

6. hydrocarbons
Organic compounds made up of the elements hydrogen and carbon only.

7. polymerization (TB pg 449, polymers)
Chemical reaction in which simple molecules (called monomers) react with each other to form large molecules (called polymers).

8. saturated
Containing single covalent bonds in its carbon atoms only.

9. unsaturated
Containing one or more double covalent carbon-carbon bonds.
(polyunsaturated means containing more than one / many double carbon-carbon covalent bonds.)

10. esterification (TB pg 443, ester)
Chemical reaction between an alcohol and a carboxylic acid, using concentrated sulphuric acid as catalyst, to produce esters (sweet smelling liquids).


Alkanes
Alkenes
Alcohols
Carboxylic acids
Definition
(n : number of carbon atoms)
Saturated hydrocarbons having the general formula CnH2n+2.
Unsaturated hydrocarbons having the general formula CnH2n.

(functional group C=C)
Organic compounds containing the hydroxyl group, -OH, with general formula CnH2n+1OH.
Organic acids containing the carboxyl group, -COOH, with general formula, CnH2n+1COOH, where n starts from zero.
First five members
(names and chemical formula)
Methane, CH4
Ethane, C2H6
Propane, C3H8
Butane, C4H10
Pentane, C5H12
Ethene, C2H4
Propene, C3H6
Butene, C4H8
Pentene, C5H10
Hexene, C6H12
Methanol, CH3OH
Ethanol, C2H5OH
Propanol, C3H7OH
Butanol, C4H9OH
Pentanol, C5H11OH
Methanoic acid, HCOOH
Ethanoic acid, CH3COOH
Propanoic acid, C2H5COOH
Butanoic acid, C3H7COOH
Pentanoic acid, C4H9COOH
Physical properties
(Trends exhibited down the group)
1. Melting point and boiling point increases.
2. Viscosity and density increases.
3. Less flammable; smokier smoke produced.
1. Melting point and boiling point increases.
2. Viscosity and density increases.
3. Less flammable; smokier smoke produced than alkanes.
1. Melting point and boiling point increases (first 4 members are liquids at rtp).
2. Solubility decreases.

1. Melting point and boiling point increases.
2. Solubility decreases.



Alkanes
Alkenes
Alcohols
Carboxylic acids
Chemical properties
1. Complete combustion gives carbon dioxide and water vapour as only products.
2. Incomplete combustion produces carbon (soot) and/or carbon monoxide and water vapour.
3. Substitution reactions occur with halogens (F2, Cl2, Br2) in uv light.


Alkanes are generally unreactive due to their saturation.
1. Complete combustion gives carbon dioxide and water vapour as only products.
2. Incomplete combustion produces carbon (soot) and /or carbon monoxide and water vapour.
3. Undergo addition reactions with
Ÿ hydrogen (hydrogenation; making of margarine);
Ÿ bromine (bromination; test for unsaturation);
Ÿ steam (production of alcohols) and
Ÿ other alkenes (polymerization)
1. Complete combustion gives carbon dioxide and water vapour as only products.
2. Oxidation
Ÿ In lab using acidified K2Cr2O7 forming carboxylic acid.
Ÿ By exposure to air (oxygen), forming carboxylic acid, due to action of bacteria in air.
3. Esterification with carboxylic acid, producing esters and water.
1. Complete combustion gives carbon dioxide and water vapour as only products.
2. Weak acids, having same chemical reactions as inorganic acids with reactive metals, bases and carbonates.
3. Esterification with alcohols, producing esters and water.
Source
1. Crude oil / petroleum
2. Cracking of larger hydrocarbons
1. Crude oil / petroleum (minor source)
2. Cracking of larger hydrocarbons
1. Catalyzed addition of steam to alkenes
2. Fermentation of simple sugars (glucose)
1. Oxidation of alcohols by
Ÿ acidified K2Cr2O7
Ÿ bacteria in air


Alkanes
Alkenes
Alcohols
Carboxylic acids
Uses
1. As a fuel.
1. To form plastics through addition polymerization.
1. As a fuel.
2. As a solvent.
3. To make alcoholic beverages.
4. To form esters.
1. To form esters.
Website for reference: http://www.chemguide.co.uk/orgpropsmenu.html

Important chemical reactions
Brief description
Conditions
Products
Chemical equations / Observations (if any)
Alkanes
Substitution with halogens
(using methane to illustrate)
Presence of uv light;
F2 / Cl2 / Br2
(with chlorine)
Mixture of chloromethane (CH3Cl); dichloromethane (CH2Cl2); trichloromethane (CHCl3); tetrachloromethane (CCl4); and hydrogen chloride (HCl)
CH4 + Cl2 à CH3Cl + HCl
CH3Cl + Cl2 à CH2Cl2 + HCl
CH2Cl2 + Cl2 à CHCl3 + HCl
CHCl3 + Cl2 à CCl4 + HCl
Any or all of the above can occur at the same time.
Reaction stops when methane and/or chlorine are used up.
Alkenes
Addition reaction with hydrogen
(Hydrogenation of ethene)
Approx 200°C;
nickel catalyst;
hydrogen gas
Ethane
Generally, the corresponding alkane is obtained.
C2H4 + H2 à C2H6

Generally, CnH2n + H2 à CnH2n+2


Important chemical reactions
Brief description
Conditions
Products
Chemical equations / Observations (if any)
Alkenes
Addition reaction with bromine
(Bromination of ethene)
Bromine solution
Dibromoethane
C2H4 + Br2 à C2H4Br2
Reddish brown bromine solution is decolourised.
A colourless product is obtained.
This is also known as the test for unsaturation.
Alkenes
Addition reaction with steam
(using ethene to illustrate)
300°C; 65 atm;
phosphoric acid as catalyst
Ethanol
Generally, the corresponding alcohol is obtained.
C2H4 + H2O à C2H5OH

Generally, CnH2n + H2O à CnH2n+1OH
Alkenes
Addition polymerization
(using ethene to illustrate)
High pressure;
high temperature;
catalyst

(1000 atm; 200°C)
Poly(ethene)

Generally, name of polymer is obtained by putting the monomer in brackets and adding ‘poly’ in front of the brackets.
E.g. polymerization of ethene

n CH2 = CH2
ethene poly(ethene)
Catalytic cracking
(for both long-chained alkanes and alkenes)
High temperature; catalyst

(about 600°C; aluminium oxide or silicon (IV) oxide as catalyst - aluminosilicates)
Mixture of short-chained alkenes and mixture of short-chained alkanes or H2 (g)
E.g. hexane à butane and ethene
C6H14 à C4H10 + C2H4
Alternatively, hexane à ethene + hydrogen
C6H14 à 3C2H4 + H2
Products obtained depend on conditions imposed.

The total number of carbon atoms and hydrogen atoms must be the same before and after cracking.


Important chemical reactions
Brief description
Conditions
Products
Chemical equations / Observations (if any)
Alcohols
Oxidation to carboxylic acids
(using ethanol to illustrate)
Oxidizing agent such as acidified K2Cr2O7 or by exposure to air
Ethanoic acid and water

Generally the corresponding carboxylic acid will be obtained.
ethanol + oxygen from O.A. à ethanoic acid + water
C2H5OH + 2[O] à CH3COOH + H2O
Orange acidified potassium dichromate (VI) turns green.

ethanol + oxygen from air à ethanoic acid + water
C2H5OH + O2 à CH3COOH + H2O
A sour liquid is obtained.
Fermentation of simple sugars (glucose)
Enzymes in yeast;
37°C;
simple sugars;
absence of air
Ethanol and carbon dioxide
glucose solution à ethanol + carbon dioxide
C6H12O6 à 2C2H5OH + 2CO2
Carboxylic acids
Reaction with reactive metals
(using ethanoic acid to illustrate)
Reactive metals
(e.g. Na)

The reactivity series of metals applies.
Organic salt + hydrogen gas
(e.g. sodium ethanoate + hydrogen)
ethanoic acid + sodium à sodium ethanoate + hydrogen
2CH3COOH + 2Na à 2CH3COO-Na+ + H2

Effervescence; colourless gas produced, extinguished lighted splint with ‘pop’.
ethanoate ion = CH3COO-


Important chemical reactions
Brief description
Conditions
Products
Chemical equations / Observations (if any)
Carboxylic acids
Reaction with bases / alkalis
(using ethanoic acid to illustrate)
Bases or alkalis
(e.g. NaOH)
Organic salt + water
(e.g. sodium ethanoate + water)
ethanoic acid + sodium hydroxide
à sodium ethanoate + water
CH3COOH + NaOH à CH3COO-Na+ + H2O

This reaction is also called a neutralization reaction.
Carboxylic acids
Reaction with carbonates
(using ethanoic acid to illustrate)
Carbonates
(e.g. Na2CO3)
Organic salt + water + carbon dioxide gas
(e.g. sodium ethanoate + water + carbon dioxide)
ethanoic acid + sodium carbonate
à sodium ethanoate + water + carbon dioxide
CH3COOH + Na2CO3 à CH3COO-Na+ + H2O + CO2

Effervescence; colourless gas produced, forms white precipitate with limewater.
Esterification
(between carboxylic acids and alcohols)
(using ethanoic acid and ethanol to illustrate)
Ethanoic acid;
ethanol;
few drops of concentrated H2SO4 as catalyst;
heat
Ester + water
(e.g. ethyl ethanoate + water)

A molecule of water is always produced when a molecule of carboxylic acid reacts with a molecule of alcohol.
ethanoic acid + ethanol à ethyl ethanoate + water
CH3COOH + C2H5OH à CH3COOC2H5 + H2O

Generally, the –H is removed from the alcohol while the –OH is removed from the carboxylic acid to form the water of molecule produced during esterification.
First part of name of ester comes from the alcohol (from –ol change to –thyl) while second part of name of ester comes from the carboxylic acid (from –oic acid change to ­–ate).


Description
Reaction
Conditions
Products
Structure of product
Esterification
(Formation of ethyl ethanoate)
Heat and few drops of concentrated H2SO4 as catalyst
Ethanol and ethanoic acid
Ethyl ethanoate
(known as esters, which are generally sweet smelling liquids / oils)



Refer to TB pg 442 for structure of ethyl ethanoate
Condensation polymerization of esters
Heat and few drops of concentrated H2SO4 as catalyst
Monomers:
Alcohol and carboxylic acid
Polyesters
Synthetic polyester:
Terylene
Natural polyester:
Fats
Refer to TB pg 456 (Structure of terylene polymer)
Condensation polymerization of amides
Heat and a few drops of concentrated H2SO4 as catalyst
Monomers:
Alcohol and amine
Polyamides
Synthetic polyamide:
Nylon
Natural polyamide:
Proteins
Refer to TB pg 455 (Structure of nylon polymer)
Addition polymerization
of ethene
High pressure (1000 atm); High temperature (200°C);
Catalyst
Monomer:
Ethene
Poly(ethene)
(also called polythene)





Refer to TB pg 450 for structure of poly(ethene) polymer
Refer to TB pg 452 Table 28.2 for details of other common polymers
End of brief notes on Organic Chemistry
© Mrs Annie (XMS Science Dept 2007)