ORG CHEM | Alcohols

Alcohol

an organic compound with a hydroxyl (OH) functional group

Nomenclature of Alcohols (Alkanes)

1. Identify the longest chain that contains the hydroxyl group.

2. Number the chain nearest to the hydroxyl group.

3. Follow the same rules when identifying and numbering substituents.

4. Assemble the name by changing -e to -ol. Put the number of the hydroxyl groups before the main name (e.g. 2-butanol)

5. If there are multiple hydroxyl groups, use suffixes like -diol or -triol depending on the number of hydroxyl groups. In these scenario, keep the -e ending of the alkane.

Nomenclature of Alcohols (Alkenes and Alkynes)

1. Identify the longest chain that contains the hydroxyl group and the double and/or triple bonds.

2. Number the chain so the hydroxyl group gets the lowest possible number. If it has the same number from both ends, then use the double or triple bond as basis.

3. Follow the same rules when identifying and numbering substituents.

4. Assemble the name by changing -e in "-ene” or “-yne” to “-enol” or “-ynol”. Specify the numbering of both the hydroxyl group (e.g. but-2-en-2-ol)

5. If there are multiple hydroxyl groups, use suffixes like -diol or -triol depending on the number of hydroxyl groups. In these scenario, keep the -e ending of the alkene or alkyne.

Primary (1º) Alcohol

the C-OH carbon is attached to one carbon

Secondary (2º) Alcohol

the C-OH carbon is attached to two carbons

Tertiary (3º) Alcohol

the C-OH carbon is attached to three carbons

Hydrogen Bonding in Alcohols

Replacing a hydrogen with an OH group allows molecules to associate through hydrogen bonding, as well as engage in hydrogen bonding with water molecules

Boiling Point of Alcohols

The hydrogen bonding also increases the boiling point of a hydrocarbon compared to hydrocarbons of the same mass. The strength of hydrogen bonds means significant energy is needed to break the intermolecular forces. However, if two hydrocarbons have the same number of hydroxyl groups, the heavier hydrocarbon will have a higher boiling point due its higher molar mass.

Solubility of Alcohols

The hydroxyl group makes smaller hydrocarbons soluble in water. However as more carbons are added, the solubility decreases.

Melting Point of Alcohols

They increase with more carbons, however are not as predictable due to molecular packing

Steric Hindrance

crowding that occurs when atoms or groups of atoms in a molecule are too close to each other

Reactivity of Alcohols

It varies between type and size, as larger alcohols can be sterically hindered in substitution reactions.

Boiling Points of Primary, Secondary, and Tertiary Alcohols

As more carbons are attached to the R-OH group, the boiling point decreases due to steric hindrance weakening hydrogen bonding.

Melting Points of Primary, Secondary, and Tertiary Alcohols

As more carbons are attached to the R-OH group, the melting point decreases due to the increased branching reducing packing efficiency and disrupting solid-state packing.

Solubility of Primary, Secondary, and Tertiary Alcohols

While primary and secondary chains have similar solubility, the tertiary alcohol has lower solubility due to larger hydrophobic alkyl groups.

Reactivity of Primary Alcohols

generally oxidized to aldehydes, then to carboxylic acids

Reactivity of Secondary Alcohols

more reactive in certain reactions and can be oxidized to ketones

Reactivity of Tertiary Alcohols

Highly reactive in substitution reactions; less likely to undergo oxidation due to steric hindrance.

Uses of Alcohols

alcoholic drinks, fuel vinegar, antiseptic, cough remedy