Review of Chemistry

Polarity of Compounds

Polarity describes the distribution of electrical charge over the atoms joined by a bond. Molecules can be classified as polar or nonpolar based on their shape and the electronegativity of their atoms.

• Polar molecules: Have an uneven distribution of electrons, resulting in a dipole moment (e.g., H2O).

• Nonpolar molecules: Have an even distribution of electrons (e.g., O2, CH4).

• Determining polarity: Consider both the polarity of individual bonds and the molecular geometry.

• Example: CO2 has polar bonds but is a nonpolar molecule due to its linear geometry.

Molecular Geometry

The shape of a molecule is determined by the number of bonding and lone pairs around the central atom, often predicted using VSEPR theory.

• Common geometries: Linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral.

• Example: CH4 is tetrahedral; H2O is bent.

Intermolecular Forces

Intermolecular forces are attractions between molecules, influencing physical properties like boiling and melting points.

• London dispersion forces: Present in all molecules, especially nonpolar ones.

• Dipole-dipole interactions: Occur between polar molecules.

• Hydrogen bonding: A strong dipole-dipole interaction involving H bonded to N, O, or F.

• Example: H2O exhibits hydrogen bonding; CH4 only has London forces.

Hydrogen Bond Donors and Acceptors

• Donor: A molecule with a hydrogen atom attached to N, O, or F.

• Acceptor: A molecule with a lone pair on N, O, or F.

• Example: In water, each molecule can act as both donor and acceptor.

Chapter 12: Introduction to Organic Chemistry – Hydrocarbons

Organic vs. Inorganic Molecules

• Organic molecules: Contain carbon and hydrogen, often with O, N, S, P, or halogens.

• Inorganic molecules: Do not primarily contain carbon-hydrogen bonds.

• Example: CH4 (organic), NaCl (inorganic).

Types of Hydrocarbons: Alkanes, Alkenes, Alkynes

• Alkanes: Only single bonds (saturated hydrocarbons).

• Alkenes: At least one double bond (unsaturated).

• Alkynes: At least one triple bond (unsaturated).

• Example: Ethane (C2H6), Ethene (C2H4), Ethyne (C2H2).

Boiling Points of Hydrocarbons

• Boiling point increases with molecular weight and decreases with branching.

• Alkanes < Alkenes < Alkynes (for similar size) due to increasing polarity.

• Example: n-Butane boils at a higher temperature than isobutane.

IUPAC Naming of Hydrocarbons

• Alkanes: Prefix (number of carbons) + -ane (e.g., methane, ethane).

• Cycloalkanes: Prefix + cyclo- + -ane (e.g., cyclopentane).

• Alkenes: Prefix + -ene (e.g., ethene).

• Alkynes: Prefix + -yne (e.g., ethyne).

• Example: CH3CH=CH2 is propene.

Aromatic Compounds

• Benzene ring: Six-carbon ring with alternating double bonds.

• Common derivatives: Toluene (methylbenzene), Phenol (hydroxybenzene).

• Example: Toluene is used as a solvent.

Classification of Carbon Atoms

• Primary (1°): Attached to one other carbon.

• Secondary (2°): Attached to two other carbons.

• Tertiary (3°): Attached to three other carbons.

• Quaternary (4°): Attached to four other carbons.

• Example: The central carbon in neopentane is quaternary.

Physical State of Alkanes at Room Temperature

• 1–4 carbons: Gases

• 5–17 carbons: Liquids

• 18+ carbons: Solids

• Example: Methane (gas), octane (liquid), paraffin wax (solid).

Combustion Reactions of Alkanes and Alkenes

• Complete combustion produces CO2 and H2O.

• General equation for alkane combustion:

• Example: Combustion of ethane:

Naming Haloalkanes

• Halogen substituents are named as prefixes (fluoro-, chloro-, bromo-, iodo-).

• Number the chain to give the lowest possible numbers to substituents.

• Example: CH3CH2Cl is chloroethane.

Saturated vs. Unsaturated Compounds

• Saturated: Only single bonds (alkanes).

• Unsaturated: Contains double or triple bonds (alkenes, alkynes).

• Example: Ethane (saturated), ethene (unsaturated).

Cis/Trans Isomerism in Alkenes

• Cis: Similar groups on the same side of the double bond.

• Trans: Similar groups on opposite sides.

• Example: cis-2-butene vs. trans-2-butene.

Addition Reactions of Alkenes and Markovnikov’s Rule

• Alkenes react with H2, halogens, or acids to form saturated products.

• Markovnikov’s Rule: In addition of HX to an alkene, H attaches to the carbon with more hydrogens.

• Example: CH2=CHCH3 + HBr → CH3CHBrCH3

Ortho, Meta, Para Naming in Aromatics

• Ortho (o-): Substituents on adjacent carbons (1,2-).

• Meta (m-): Substituents separated by one carbon (1,3-).

• Para (p-): Substituents opposite each other (1,4-).

• Example: p-dichlorobenzene (1,4-dichlorobenzene).

Chapter 13: Alcohols, Phenols, Thiols, and Ethers

Naming Alcohols

• Replace the -e of the alkane with -ol.

• Number the chain to give the -OH group the lowest possible number.

• Example: CH3CH2OH is ethanol.

Classification of Alcohols

• Primary (1°): -OH on a carbon attached to one other carbon.

• Secondary (2°): -OH on a carbon attached to two other carbons.

• Tertiary (3°): -OH on a carbon attached to three other carbons.

• Example: Isopropanol is a secondary alcohol.

Alcohols and Health

• Small alcohols (e.g., ethanol) are used in beverages; methanol is toxic.

• Chronic consumption can damage the liver and nervous system.

Naming Thiols and Ethers

• Thiols: Add "thiol" to the alkane name (e.g., methanethiol).

• Ethers: Name the two alkyl groups followed by "ether" (e.g., ethyl methyl ether).

Boiling Points of Alcohols, Thiols, and Ethers

• Alcohols > Thiols > Ethers (for similar size) due to hydrogen bonding in alcohols.

• Example: Ethanol boils at 78°C, diethyl ether at 35°C.

Solubility of Alcohols and Thiols

• Small alcohols are soluble in water due to hydrogen bonding.

• Solubility decreases as hydrocarbon chain length increases.

• Thiols are less soluble than alcohols.

Oxidation of Alcohols and Thiols

• Primary alcohols oxidize to aldehydes, then carboxylic acids.

• Secondary alcohols oxidize to ketones.

• Tertiary alcohols do not oxidize easily.

• Common oxidizing agents: KMnO4, H2O2.

• Thiols oxidize to disulfides.

• Example:

Dehydration of Alcohols and Zaitsev’s Rule

• Alcohols lose water to form alkenes (dehydration), usually with acid catalyst.

• Zaitsev’s Rule: The major product is the more substituted alkene.

• Example: Dehydration of 2-butanol yields 2-butene as the major product.

Additional info: Table compares boiling points and solubility of different functional groups, illustrating the effect of hydrogen bonding and molecular structure.