organic_chemistry
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Organic Chemistry
Prepared By: Ms. Taban Ahmed
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Definition of Organic Chemistry
The study of compounds present in living organisms.
All organic compounds contain carbon.
Organic chemistry is fundamentally the chemistry of carbon.
Natural Sources of Organic Compounds
Compounds derived from living things include:
Carbohydrates
Proteins
Fats
Vitamins
Antibiotics
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A variety of organic products obtained from living things.
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Sources of Organic Compounds
Crude oil or coal provides:
Alkanes, Alkenes, Alkynes
Aromatic hydrocarbons
Methods of extraction include:
Fractional distillation
Destructive distillation
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Historical Definition of Organic Chemistry (Pre-1800s)
Organic chemistry was defined based on compounds obtained from living organisms.
It was believed that organic compounds could only be synthesized in living organisms.
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Modern Definition of Organic Chemistry
Many organic compounds are now recognized to be synthesized from inorganic substances.
Current definition:
The study of carbon compounds, excluding CO, CO2, carbonates, hydrogen carbonates, carbides, and cyanides.
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Development of Organic Chemistry as a Science
Historical distinction:
Organic compounds: obtained from living organisms.
Inorganic compounds: obtained from non-living sources.
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Key Event in Organic Chemistry Development
In 1828, German chemist Wohler synthesized urea from ammonium cyanate.
Reaction:
Heat applied to ammonium cyanate produced urea, showcasing synthesis beyond living organisms.
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Redefining Organic Chemistry
It is the study of carbon compounds obtained from natural sources or synthesized in laboratories, excluding traditional inorganic categories.
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Properties of Carbon Atoms
Each carbon atom has four unpaired electrons.
Tends to form four strong covalent bonds.
Capable of forming chains, branched chains, and rings due to its catenation ability.
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Examples of Carbon Compounds
Methane (CH4)
Carbon dioxide (CO2)
DNA
Benzene
Ethanol
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Examples of Organic Compounds
Paper (Cellulose)
Nail Polish (Nitrocellulose, butyl acetate)
Candle (Wax, tallow)
Fabric (Nylon, rayon)
Soap (Fatty acid salt)
Gasoline (Mixed hydrocarbons)
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Examples of Inorganic Compounds
Salt
Diamond
Water
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Catenation of Carbon
High strength of carbon-carbon bonds (bond enthalpy of 356 kJ/mol) explains its ability to catenate.
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Classification of Organic Compounds
Hydrocarbons: simplest organic compounds consisting only of carbon and hydrogen.
Main groups:
Saturated hydrocarbons - single carbon-carbon bonds.
Unsaturated hydrocarbons - have double or triple carbon-carbon bonds.
Aromatic hydrocarbons - contain a benzene ring.
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Aromatic Hydrocarbons
Contain benzene rings with alternating single and double carbon-carbon bonds described by resonance formulas.
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Molecular Models of Hydrocarbons
Visual representations of the structures of different hydrocarbons.
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Alkanes
Acyclic, saturated hydrocarbons with general formula CnH2n+2.
Simplest alkane: Methane (CH4).
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Three-Dimensional Model of Methane
Methane has a tetrahedral structure with bond angles of 109.5 degrees.
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Structural Formulas for Alkanes
Methane - CH4
Ethane - C2H6
Propane - C3H8
Butane - C4H10
Illustrate the straight-chain (normal) alkanes.
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Condensed Structural Formulas
Often used in organic chemistry for clarity, omitting explicit hydrogen atoms:
Examples:
Methane: CH4
Ethane: CH3CH3
Propane: CH3CH2CH3
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Constitutional Isomerism and Branched-Chain Alkanes
Isobutane (2-methylpropane) structure as an example of a branched-chain alkane.
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Structure of Isobutane
Visual representation:
H H
CH3 - C - CH2 - CH3
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Isomerism in Alkanes
Isobutane (C4H10) is a constitutional isomer of normal butane, sharing the same molecular formula but differing structurally.
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Models of Isobutane and Butane
Visual perspectives of isobutane and butane.
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Cycloalkanes
Cycloalkanes are cyclic, saturated hydrocarbons with general formula CnH2n, with carbon atoms joined in a ring.
Example: Structure of cyclobutane.
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Sources and Uses of Alkanes and Cycloalkanes
Principal sources: Fossil fuels (mixtures of alkanes, cycloalkanes, aromatic hydrocarbons).
Alkanes as starting points for:
Plastics
Pharmaceuticals
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Alkenes and Alkynes
Alkenes and alkynes: unsaturated hydrocarbons with double or triple carbon-carbon bonds.
Hydrogenation can convert them to saturated compounds.
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Alkenes and Their Isomers
General formula for alkenes: CnH2n.
Simplest alkene: Ethylene.
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Geometric Isomers of Alkenes
Isomers where atoms occupy different relative positions in space.
Example: Cis-2-butene and trans-2-butene.
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Alkynes
Unsaturated hydrocarbons with carbon-carbon triple bonds.
General formula: CnH2n-2.
Simplest alkyne: Acetylene (ethyne).
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Aromatic Hydrocarbons
Characterized by six-membered benzene rings with alternating single and double bonds.
Example structures include benzene and toluene.
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Examples of Aromatic Hydrocarbons
Perfume
Vanilla extract
Cinnamon
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Combustion of Alkanes
All hydrocarbons burn in excess oxygen, producing carbon dioxide, water, and heat.
Example: Reaction in propane gas grill.
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Substitution Reactions of Alkanes
A substitution reaction involves an atom being replaced by another atom in a hydrocarbon.
Example: Reaction of ethane with Cl2.
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Ethane and Chlorination Reaction
Example Reaction:
H H
H - C - C - H + Cl2 → H - C - C - Cl + H-Cl
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Oxidation Reactions of Alkenes
Alkenes combust in oxygen;
Partial oxidation example with potassium permanganate results in color change (purple to brown).
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Addition Reactions of Alkenes
Alkenes are more reactive than alkanes due to double bond.
Example: Br2 addition to propene creates a saturated compound.
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Reaction Example for Addition of Halogens
CH3-CH=CH2 + Br2 → CH2Br-CHBr-CH3
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Naming Hydrocarbons
IUPAC naming rules for branched-chain alkanes:
Determine the longest chain.
Base name corresponds to number of carbon atoms.
Include branches in the full name.
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Steps for Naming
Find the longest continuous carbon chain.
Example: CH3-CH2-CH2-CH3.
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Steps for Naming
Name the branches as alkyl groups.
Reference Table of common alkyl groups.
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Steps for Naming
Number the branches based on their position on the longest chain, starting from the closest end.
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Steps for Naming
For multiple branches of the same type, use prefixes like di-, tri-, tetra-, with indicating locations.
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Reiteration of Naming Steps
Follow the structured approach for naming alkanes.
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Nomenclature of Alkenes and Alkynes
Naming follows similar rules as alkanes; endings change to –ene (alkenes) and –yne (alkynes).
Position of double/triple bonds indicated in names.
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Isomerism in Alkenes
Mention of cis and trans isomers in naming conventions.
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Derivatives of Hydrocarbons
Definition of functional group; reactive portions of molecules.
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Classification of Organic Compounds
Based on functional groups present in compounds.
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Example of Functional Groups
Comparison of propane and ethanol:
Propane: No reaction with sodium.
Ethanol: Reacts with sodium to produce hydrogen gas.
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Similarities Among Alcohols
Compounds exhibiting -OH functional group share similar properties and fall into the same homologous series.
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Homologous Series Definition
A series of compounds with the same functional group, differing by –CH2–.
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General Structure for Homologous Series
Examples identify members based on carbon atom count and structural formulas.
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Summary of First Four Straight-Chain Alkanes
Identification based on molecular formulas and IUPAC names:
Methane: CH4, Ethane: C2H6, Propane: C3H8, Butane: C4H10.
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Continuation of Structural Examples
Detailed structural formulae for the first four members of straight-chain alkanes.
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Features of Straight-Chain Alkanes
All members of a homologous series can be represented by a general formula highlighting trends in properties.
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Chemical Properties of Members
Similar chemical properties across members; gradual changes in physical properties relate to molecular mass.
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Data on Physical Properties
Table of the first 20 straight-chain alkanes:
Gas or liquid states; identified melting/boiling points.
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Physical Properties Continued
Properties for higher members of the alkane series, demonstrating trends.
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Functional Group Identification Example
Identify functional groups such as:
Carbon-carbon double bond, chlorino group in organic compounds.
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Additional Functional Groups
Identify amino (-NH2) and carboxyl (-COOH) groups in compounds.
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Homologous Series Identification Example
Classify compounds like esters and amides based on structure.
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Functional Group Classification
Examine series for amide and anhydride compounds.
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Analyzing Homologous Series
Examples provided for comparing compound classifications based on functional groups.
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Conclusion of Series Classification
Affirmative/Negative answers concluded for different pairs based on functional groups.
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Thank you!