Exam 1 Study Guide: GOB Chemistry – Molecular Structure, Intermolecular Forces, and Introduction to Organic Chemistry

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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.

Compound	Boiling Point (°C)	Solubility in Water
Methanol (alcohol)	65	High
Ethanethiol (thiol)	35	Moderate
Diethyl ether (ether)	35	Low
Hexane (alkane)	69	Very low

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