Chapters 11, 12, and 14: Introduction to Organic Chemistry, Hydrocarbons, and Functional Groups

Introduction to Organic Chemistry

Organic vs. Inorganic Compounds

Organic chemistry is the study of compounds containing carbon, typically bonded to hydrogen, oxygen, nitrogen, or other carbon atoms. Inorganic compounds generally do not contain carbon-hydrogen bonds.

• Organic Compounds: Contain carbon atoms, usually bonded to hydrogen, and often form large, complex molecules. Examples: methane (CH4), glucose (C6H12O6).

• Inorganic Compounds: Typically do not contain C-H bonds. Examples: NaCl, H2O, CO2.

Key Point: Every carbon atom in an organic compound forms four covalent bonds, which may be single, double, or triple bonds.

Hydrocarbons: Structure and Classification

Saturated vs. Unsaturated Hydrocarbons

Hydrocarbons are compounds composed only of carbon and hydrogen. They are classified based on the types of bonds between carbon atoms.

• Saturated Hydrocarbons (Alkanes): Contain only single bonds between carbon atoms. Each carbon is bonded to as many hydrogens as possible.

• Unsaturated Hydrocarbons: Contain one or more double (alkenes) or triple (alkynes) bonds between carbon atoms.

Example: Ethane (C2H6) is saturated; ethene (C2H4) is unsaturated.

Formulas for Organic Compounds

• Molecular Formula: Shows the number and type of atoms (e.g., C2H6).

• Condensed Structural Formula: Groups atoms to show connectivity (e.g., CH3CH3).

• Expanded Structural Formula: Shows all bonds between atoms.

• Line-Angle Formula: Uses lines to represent carbon-carbon bonds; vertices and line ends represent carbon atoms, and hydrogens are implied.

Alkanes and Cycloalkanes

Definition and Nomenclature

• Alkane: A saturated hydrocarbon with only single bonds. General formula: $C_nH_{2n+2}$

• Cycloalkane: A saturated hydrocarbon with carbon atoms arranged in a ring. General formula: $C_nH_{2n}$

Naming Alkanes: Use the IUPAC system, which includes a prefix for the number of carbons and a suffix "-ane" (e.g., methane, ethane, propane). For branched alkanes, identify the longest chain and name substituents as prefixes.

Naming Cycloalkanes: Add the prefix "cyclo-" to the alkane name (e.g., cyclopentane).

Drawing and Naming Practice

• Given a condensed formula, identify the parent chain and substituents to assign the correct IUPAC name.

• Given an IUPAC name, draw the corresponding condensed structural formula.

• For cycloalkanes, interpret line-angle formulas to determine the ring size and substituents.

Isomerism in Organic Compounds

Structural Isomers

Structural isomers are compounds with the same molecular formula but different connectivity of atoms.

• Isomers have different physical and chemical properties.

• To determine if two molecules are isomers, compare their connectivity and arrangement.

Cis-Trans (Geometric) Isomerism

Occurs in alkenes (and some cycloalkanes) when two different groups are attached to each carbon of a double bond or ring.

• Cis-isomer: Similar groups are on the same side of the double bond or ring.

• Trans-isomer: Similar groups are on opposite sides.

Example: 2-butene has both cis- and trans- isomers.

Alkenes and Alkynes: Functional Groups and Reactions

Recognizing Functional Groups

• Alkene: Contains a carbon-carbon double bond ($C=C$).

• Alkyne: Contains a carbon-carbon triple bond ($C\equiv C$).

Common Reactions of Alkenes and Alkynes

• Hydrogenation: Addition of H2 across a double or triple bond to form an alkane.

• Halogenation: Addition of halogens (Cl2, Br2) across a double or triple bond.

• Hydration: Addition of water (H2O) across a double bond to form an alcohol.

Example: Hydrogenation of ethene ($CH_2=CH_2$) yields ethane ($CH_3CH_3$).

Identifying Functional Groups

Functional groups are specific groups of atoms within molecules that determine the characteristic chemical reactions of those molecules.

• Alkane: Single C–C bonds

• Alkene: C=C double bond

• Alkyne: C≡C triple bond

• Alcohol: –OH group

• Aldehyde: –CHO group

• Ketone: C=O group within carbon chain

• Carboxylic Acid: –COOH group

• Ester: –COOR group

• Amine: –NH2, –NHR, or –NR2 group

• Amide: –CONH2 group

Summary Table: Key Hydrocarbon Types and Their Features

Type	General Formula	Bonding	Example
Alkane	$C_nH_{2n+2}$	Single bonds	Methane (CH4)
Alkene	$C_nH_{2n}$	At least one double bond	Ethene (C2H4)
Alkyne	$C_nH_{2n-2}$	At least one triple bond	Ethyne (C2H2)
Cycloalkane	$C_nH_{2n}$	Ring structure, single bonds	Cyclohexane (C6H12)

Additional info:

• For IUPAC naming, always number the carbon chain to give the lowest possible numbers to substituents.

• Structural isomers differ in the connectivity of their atoms, not just their arrangement in space.

• Cis-trans isomerism is only possible when each carbon of the double bond has two different groups attached.