Organic Chemistry: Alkene and Alkyl Halide Preparation

Alkane Nomenclature and Structure

• 'Iso': Indicates a methyl group on the second carbon of the chain. For instance, isobutane signifies a methyl group on the second carbon of a four-carbon chain.
• 'Neo': Indicates the presence of a quaternary carbon atom at one end of the chain. For example, neopentane has a quaternary carbon at one end of the chain.

Physical Properties of Alkanes

• The first four members of alkanes (methane, ethane, propane, and butane) are gases at room temperature.
• The boiling points of unbranched alkanes increase as the molecular weight increases. This is due to stronger London dispersion forces between larger molecules.
• Alkanes are insoluble in water because they are nonpolar and water is polar.

Reactions of Alkanes

• Combustion: Alkanes react with oxygen to produce carbon dioxide, water, and heat. For example, the combustion of propane (CH3CH2CH3) with oxygen produces carbon dioxide (CO2), water (H2O), and heat.
• Halogenation: Alkanes react with halogens (like chlorine or bromine) in the presence of light or heat to form alkyl halides.

Cycloalkanes

• A cycloalkane with six carbon atoms in the ring is called cyclohexane.

Reactions of Cycloalkanes

• Ring-opening Reactions: Cyclopropane and cyclobutane undergo ring-opening reactions to relieve strain and yield more stable open-chain compounds.

Elimination Reactions

• Alkene Formation: The elimination of a molecule of hydrogen halide from alkyl halides results in the formation of an alkene.

Alkene Properties

• Compared to alkanes, alkenes are slightly more soluble in water due to the presence of a C=C double bond, which can form weak hydrogen bonds with water molecules.

E2 Mechanism

• The E2 mechanism is a type of elimination reaction where the base removes a β-hydrogen atom from the carbon atom adjacent to the one bearing the leaving group.

Other Reactions

• When alcohols are heated with strong acids, they can undergo dehydration reactions, forming alkenes.
• Dihalogen derivatives of alkanes, when treated with sodium or zinc, undergo dehalogenation reactions, forming alkenes.

SN1 Reactions

• The SN1 mechanism involves ionization of the substrate to form a carbocation as the rate-determining step.

Test your knowledge of organic chemistry preparation reactions, including the catalytic hydrogenation of alkenes and the reduction of alkyl halides. Explore nomenclature rules for naming branched alkanes and alkyl groups.