General Chemistry: Organic Chemistry Fundamentals – Study Guide

Organic Chemistry Fundamentals

Properties of Alkanes

Alkanes are saturated hydrocarbons with only single bonds between carbon atoms. They exhibit characteristic physical and chemical properties.

• Nonpolar molecules: Alkanes are nonpolar due to similar electronegativities of carbon and hydrogen.

• Low melting and boiling points: Compared to other organic compounds, alkanes have relatively low melting and boiling points, which increase with molecular size.

• Insoluble in water: Alkanes do not dissolve in water but are soluble in nonpolar solvents.

• Weak intermolecular forces: Only London dispersion forces are present.

• Chemically inert: Alkanes are less reactive than alkenes or alkynes.

Example: Methane (CH4) is a simple alkane, gaseous at room temperature, and insoluble in water.

Bonding in Alkenes

Alkenes are hydrocarbons containing at least one carbon-carbon double bond. The bonding in alkenes involves sigma and pi bonds.

• Sigma (σ) bond: Formed by head-on overlap of orbitals; present in all single bonds.

• Pi (π) bond: Formed by side-to-side overlap of p orbitals; present in double and triple bonds.

• Alkene double bond: Consists of one sigma bond and one pi bond.

Example: Ethene (C2H4) has a double bond between the two carbon atoms.

Nomenclature of Organic Compounds

Systematic naming (IUPAC) of organic molecules follows specific rules to ensure each compound has a unique name.

• Longest carbon chain: Identify the longest continuous chain as the parent hydrocarbon.

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

• Substituents: Name and number all branches or functional groups.

• Alphabetical order: List substituents alphabetically in the name.

Example: 2-ethyl-3,5-dimethylhexane: A hexane chain with ethyl at C2 and methyl groups at C3 and C5.

Types of Carbon Atoms

Carbons in organic molecules are classified by the number of other carbons to which they are attached.

• 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: In isobutane, the central carbon is tertiary.

Unsaturated Hydrocarbons

Unsaturated hydrocarbons contain at least one double or triple bond.

• Alkenes: Contain C=C double bonds.

• Alkynes: Contain C≡C triple bonds.

• Properties: More reactive than alkanes due to the presence of π bonds.

Example: Ethyne (acetylene) is an alkyne.

Bond Angles in Organic Molecules

The geometry around atoms in organic molecules is determined by hybridization.

• sp3 hybridization: Tetrahedral, bond angle ≈ 109.5°

• sp2 hybridization: Trigonal planar, bond angle ≈ 120°

• sp hybridization: Linear, bond angle ≈ 180°

Example: The bond angle in a planar amide group is approximately 120°.

Halogenation of Alkanes

Halogenation is a substitution reaction where a hydrogen atom is replaced by a halogen.

• Monochlorination: Only one hydrogen is replaced by chlorine.

• Number of products: Depends on the number of unique hydrogens in the molecule.

Example: Monochlorination of pentane can yield several isomers.

Isomerism in Organic Chemistry

Isomers are compounds with the same molecular formula but different structures.

• Structural isomers: Differ in connectivity of atoms.

• Cis-trans (geometric) isomers: Occur in alkenes due to restricted rotation around double bonds.

• Conformational isomers: Differ by rotation around single bonds.

Example: 2-butene has cis and trans isomers.

Physical Properties: Boiling Points

Boiling points of organic compounds depend on molecular weight, branching, and intermolecular forces.

• Smaller molecules: Lower boiling points.

• Branching: More branching lowers boiling point.

• Intermolecular forces: Stronger forces (e.g., hydrogen bonding) increase boiling point.

Example: Among pentane, butane, and decane, butane has the lowest boiling point.

Hydration and Hydrohalogenation Reactions

These are addition reactions involving alkenes.

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

• Hydrohalogenation: Addition of HX (e.g., HCl) across a double bond to form alkyl halides.

• Markovnikov's Rule: The hydrogen atom adds to the carbon with more hydrogens; the halide adds to the more substituted carbon.

Example: Hydration of propene yields 2-propanol.

Polymerization

Polymerization is the process of linking monomers to form polymers.

• Initiation: Formation of reactive species (radical, cation, or anion).

• Propagation: Chain growth by successive addition of monomers.

• Termination: Chain ends by combination or disproportionation.

Example: Polymerization of ethene forms polyethylene.

Chirality and Stereochemistry

Chirality refers to the property of a molecule that is not superimposable on its mirror image.

• Chiral center: A carbon atom bonded to four different groups.

• Enantiomers: Non-superimposable mirror images.

Example: 2-butanol contains a chiral center at the second carbon.

Types of Organic Reactions

Organic reactions are classified by the type of transformation occurring.

• Substitution: One atom or group replaces another.

• Addition: Atoms are added to a double or triple bond.

• Elimination: Atoms are removed, forming a double or triple bond.

• Rearrangement: The structure of the molecule is reorganized.

Example: Chlorination of methane is a substitution reaction.

Common Organic Functional Groups

Functional groups determine the chemical reactivity of organic molecules.

• Alcohols: Contain -OH group.

• Alkenes: Contain C=C double bond.

• Alkynes: Contain C≡C triple bond.

• Carboxylic acids: Contain -COOH group.

• Amines: Contain -NH2 group.

Example: Ethanol is an alcohol; acetic acid is a carboxylic acid.

Table: Types of Isomerism

Type of Isomerism	Description	Example
Structural	Different connectivity	Butane vs. isobutane
Cis-trans (Geometric)	Different spatial arrangement around double bond	cis-2-butene vs. trans-2-butene
Conformational	Rotation around single bonds	Staggered vs. eclipsed ethane
Enantiomers	Non-superimposable mirror images	(R)-2-butanol vs. (S)-2-butanol

Additional info:

• Some questions reference specific molecular structures and require drawing or visual identification, which are not reproduced here but are described in the context of the relevant topic.

• For detailed mechanisms (e.g., polymerization, Markovnikov's rule), refer to standard organic chemistry textbooks for stepwise illustrations.