UNIT 5 ORGANIC CHEMISTRY

What makes a compound organic? Organic compounds –Contain both carbon and hydrogen, Ex. C 6 H 12 O 6 Inorganic compounds –Do not contain both carbon and hydrogen Ex. H 2 O, CO 2

Hydrocarbons Compounds that contain only hydrogen and carbon atoms Most come from living sources: fossil fuels (decomposition of once-living organisms)

Classification: 1. aliphatic: open-chain or cyclic - includes alkanes, alkenes, alkynes and alicyclics (ring structures) 2. aromatic: cyclic hydrocarbons where some electrons are shared, ex. benzene

1. ALIPHATIC  Classified by the kinds of carbon-carbon bonds in their molecules –Saturated: containing only single C-C bonds –Unsaturated: containing at least one double or triple bond between carbon atoms

a. Alkanes Saturated Hydrocarbons –nonpolar –general formula C n H 2n+2

Cows frequently produce methane after consumption of grass... Penguins usually don't...

Alkane nomenclature Methane : 1C –Product of anaerobic decomposition –Formula: CH 4 –Structural formula:

Ethane: 2C –Formula: C 2 H 6 –Condensed formula: CH 3 -CH 3 –Structural formula: Propane: 3C –Formula: C 3 H 8 –Condensed formula: CH 3 -CH 2 -CH 3 –Structural formula:

A special case: cyclohexane cyclical alkanes are named by adding cyclo- in front of name, ex. cyclohexane

Properties of Alkanes: 1. boiling point: increases with the number of C atoms - the longer the chain the greater the intermolecular forces - branched-chain alkanes have a lower b.p. than straight-chain alkanes with the same number of C atoms

2. melting point: - increases with the mass and chain length 3. density - increases with chain length 4. solubility - non-polar, therefore not water soluble, dissolve in other non-polar substances

b. Alkenes: Unsaturated Hydrocarbons contain one or more double bonds general formula C n H 2n C H H H C H H H C H H2H2 H + C H H C2H6C2H6 C2H4C2H4

C H H H C H H H H.... CH H HC H H CH H HC H HH +.. C H H HH + C H H C H H + C H H H2H2 UNSATURATED HYDROCARBON SATURATED HYDROCARBON

Properties of Unsaturated Hydrocarbons nonpolar more reactive than alkanes lower boiling point than alkanes ex. ethane: -89 o C, ethene: -104 o C, library.thinkquest.org/C005377/content/images/ethene.gif

Alkene Nomenclature - "ane" is replaced by "ene" 2 carbon atoms a double bond ETHENE C2H4C2H4 CC H HH H

Alkenes are hydrocarbons that contain at least one double bond 3 carbon atoms a double bond PROPENE C3H6C3H6 CCC H H H H H H

But… How do you tell these two apart? 1-butene 2-butene

SO… 1)the “butene” tells you how many C we have CCCC 2) the “ene” tells you there is a double bond 3) the numerical prefix (ex. 2- ) tells you which carbon the double bond is on 4) Fill in the bonds and the H’s! H H H HH H H H

What about funny-looking things like this… -Find the longest C-chain: prop -Find the ending: ene -Locate the additional group, changing its ending to “yl”: meth-yl -Locate the double bond -Put it all together: methylpropene

When two or more double bonds are present the ending –diene (or –triene etc.) is used and two numbers are required to specify the position of the double bonds Ex. 1,3 - butadiene

c. Alkynes: unsaturated hydrocarbons Contain one or more triple bonds General formula C n H 2n-2

Alkyne nomenclature "ane" is replaced by "yne" Ex. ethyne Ex. propyne

2. Aromatics:ex. benzene Aromatic cyclical alkene electron distribution can vary

ISOMERS - compounds that have the same molecular formula but a different molecular structure

a) Structural Isomers (“Positional Isomers”) Ex. 1-butene vs. 2-butene - differ in the position of the multiple bond

b) geometric isomers (stereoisomers or cis-trans isomers) - have atoms that are connected in the same order but with different three-dimensional arrangements ex. cis-2-butene (both methyl groups are on the same side of the double bond) trans-2-butene (methyl groups on opposite sides)

REACTIONS OF HYDROCARBONS

- alkenes and alkynes are more chemically reactive than alkanes -double and triple bonds are easily converted to single bonds

1. Combustion Reactions All hydrocarbons are combustible (they burn) Combustion can be –i. complete: excess oxygen is present + energy

ii. Incomplete: there is not enough oxygen present: CH 4 (g) + O 2 (g)  C (s) + 2 H 2 O(l) 2 CH 4 (g) + 3 O 2 (g)  2 CO (g) + 4 H 2 O(l)

The combustion of hydrocarbons is always exothermic: it releases energy Law of conservation of energy: –Energy can be neither created nor destroyed

During a chemical reaction (ex. combustion) two things have to happen: 1. bonds have to be broken: requires energy 2. new bonds have to form: releases energy Energy change: the difference between energy required and energy released

Exothermic reactions - energy released by product formation is greater than energy needed to break bonds Endothermic reactions - energy released by product formation is lesser than energy required to break bonds

Thermochemical equation - a balanced chemical equation in which the heat of reaction is included: + energy

2. Addition Reactions - a reaction of an alkene or alkyne in which a molecule is added across a multiple bond C H H H C H H H C2H6C2H6 C H H2H2 H + C H H C2H4C2H4

Addition reactions with other compounds Works through the same mechanism as addition of H 2 ex. ethene and chlorine gas --> chloroethane CHH H C H Cl C 2 H 5 Cl 2 C H Cl 2 H + C H H C2H4C2H4

3. Substitution Reactions Involve alkanes: react chemically by replacing hydrogen atoms with other atoms, require energy Ex. CH 4 (g) + Cl 2 (g)  CH 3 Cl (g) + HCl (g) UV light

4. Polymerization Reactions joining of identical units to form a large organic molecule:

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