Tetrahedral Carbon

Saturated Organic Compounds

Saturated organic compounds contain only single bonds between carbon atoms, which results in a tetrahedral arrangement around each carbon atom.

The carbon atoms in these compounds are bonded to four other atoms (typically hydrogen or other carbons) via single covalent bonds, forming a 3D structure with bond angles of 109.5°. Alkanes are the simplest saturated hydrocarbons.

Alkanes

Alkanes are a homologous series of saturated hydrocarbons with the general formula $CₙH₂ₙ₊₂$. Each carbon atom in an alkane forms four sigma (σ) bonds, either with hydrogen or other carbon atoms.

Physical Properties of Alkanes

• State: Lower members ($C₁–C₄$) are gases at room temperature, while higher alkanes are liquids or solids.
• Solubility: Alkanes are non-polar molecules, so they are insoluble in water but soluble in non-polar solvents such as hexane or benzene.

Use as Fuels

Alkanes, particularly methane, propane, and butane, are commonly used as fuels due to their highly exothermic combustion reactions.

Chloroalkanes

Chloroalkanes are compounds where one or more hydrogen atoms in an alkane are replaced by chlorine atoms. Their general formula is $CₙH₂ₙ₊₁Cl$.

Structure and Nomenclature (Up to $C-4$)

Physical Properties of Chloroalkanes

• State: Lower members are gases or volatile liquids.
• Solubility: Chloroalkanes are generally insoluble in water but soluble in organic solvents.

Uses

• Chloroalkanes are used as solvents for grease and oil removal and in dry cleaning.

Alcohols

Alcohols are organic compounds containing the hydroxyl group ($-OH$) as their functional group. Their general formula is $R-OH$, where $R$ is an alkyl group.

Structure and Nomenclature (Up to $C-4$)

Physical Properties of Alcohols

• State: Lower members ($C₁-C₄$) are liquids at room temperature.
• Solubility: Alcohols are soluble in water due to hydrogen bonding between the hydroxyl group and water molecules. However, solubility decreases as the alkyl chain length increases.
  • Methanol is highly soluble in water.
  • Butan-1-ol has a lower solubility in water but dissolves well in non-polar solvents like cyclohexane.

Comparison of Alcohols and Water

• Both alcohols and water can form hydrogen bonds, which accounts for their similar solubility properties.
• Alcohols have a hydrocarbon tail ($R$-group), making them less polar than water, but the $OH$group allows for hydrogen bonding.

Alcohol Uses

• Ethanol is widely used as a solvent and is also produced via fermentation, commonly used in the brewing and distilling industries.
• Methanol is used as a denaturing agent in industrial alcohol to make it undrinkable.

Solubility Comparison of Alcohols: Methanol and Butan-1-ol

Solubility is determined by the type of interactions between the solute (the substance being dissolved) and the solvent (the dissolving medium). In the case of alcohols like methanol and butan-1-ol, solubility depends on the balance between the polar hydroxyl group ($-OH$) and the non-polar alkyl chain ($R$-group).

Methanol ($CH₃OH$)

Polar nature:

• Methanol has a very short alkyl chain ($CH₃$), meaning that its structure is mostly polar due to the dominant influence of the hydroxyl group. Solubility in water:

• Methanol is highly soluble in water because it can form hydrogen bonds with water molecules.

• The polar $-OH$ group interacts strongly with water, which is also a polar solvent, through hydrogen bonding. Solubility in cyclohexane:

• Methanol has limited solubility in non-polar solvents like cyclohexane.

• The polar $-OH$ group doesn't interact well with the non-polar cyclohexane molecules, but due to the short alkyl chain, methanol can still dissolve to some extent.

Butan-1-ol ($C₄H₉OH$)

Polar and non-polar regions:

• Butan-1-ol has a longer non-polar alkyl chain ($C₄H₉$), which makes it less polar overall compared to methanol.

• However, it still has a polar hydroxyl group ($-OH$) capable of forming hydrogen bonds. Solubility in water:

• Butan-1-ol is less soluble in water compared to methanol.

• While the $-OH$ group can still form hydrogen bonds with water molecules, the long non-polar alkyl chain reduces the molecule's ability to interact with water.

• The longer the non-polar chain, the less soluble the alcohol becomes in water. Solubility in cyclohexane:

• Butan-1-ol is more soluble in cyclohexane than methanol because the longer non-polar alkyl chain can interact with the non-polar molecules of cyclohexane through van der Waals forces.

• In this case, the non-polar tail of butan-1-ol "likes" the non-polar environment of cyclohexane, making it easier for the alcohol to dissolve.