10.3 Alcohols These compounds have an -OH attached to the carbon chain. This functional group is called a hydroxyl group. Note: The oxygen is bonded to the carbon in a covalent bond. The hydrogen is then bonded in a covalent bond to the oxygen, it is not a hydroxide ion that is attached to the carbon atom.

Classes of Alcohols The number of R groups attached to the carbon with the hydroxyl group is used to classify alcohols as primary, secondary or tertiary alcohols:

Primary alcohol, where only one R group is attached to the carbon to which the hydroxyl group is attached: R - CH2 - OH Secondary alcohol, where two R groups are attached to the carbon to which the hydroxyl group is attached: R1 I R2 - CH - OH

Tertiary alcohol, where three R groups are attached to the carbon to which the hydroxyl group is attached: R1 I R2 - C – OH R3

Naming Alcohols Determine the parent alkane as the longest continuous chain that includes the carbon attached to the -OH group. Number the carbons in this chain so that the carbon attached to the -OH group has the lowest number. Drop the -e ending from the name of the parent alkane and replace it with –ol Alcohols containing two or three -OH groups are called diols and triols.

Common Names of Alcohols Many alcohols have common names based on naming the hydrocarbon chain as an alkyl group and adding the word alcohol. For example: IUPAC name: Common name: Structural formula: methanol methyl alcohol CH3 - OH ethanol ethyl alcohol CH3 - CH2 - OH propan-1-ol 1-propyl alcohol CH3-CH2-CH2 - OH These are all primary alcohols

Example of a diol ethane-1,2-diol or ethylene glycol CH2 - CH2 I I OH OH

Alcohols with an aromatic ring are called phenols: 2-methylphenol (o-cresol) phenol

Cyclic Alcohols C6H11OH(l) is a cyclohexanol. The following diagram is for cyclohexane-1,2-diol OH OH OH

Properties of Alcohols Intermolecular hydrogen bonding is possible since the -OH group is slightly polar, therefore boiling points are quite high and so even the smallest alcohols are liquids at room temperature. Due to the slight polarity of the -OH group, small chain alcohols, up to 4C, are soluble in water but from 5C up alcohols have limited solubility due to the non-polar nature of the C chains.

pentan-1-ol pentan-2-ol pentan-3-ol 2-methylbutan-1-ol 2-methylbutan-2-ol 3-methylbutan-2-ol 2,2-dimethylpropanol 3-methylbutan-1-ol

Elimination Reactions Elimination reactions are essentially the reverse of the addition reactions we saw above. Halogens or hydroxyl groups are removed or eliminated from the molecule to produce a double bond in an alkene.

Elimination For example: elimination of a halogen: H H H H H H I I I I I I H - C - C - C – H + OH-  H - C = C - C – H + HOH + Br- I I I I H Br H H   2-bromopropane propene

Elimination H H H H Or: the elimination of water: I I acid I I H - C - C– H  H - C = C – H + HOH I I H OH ethanol ethene

Elimination Elimination reactions are important as they produce useful unsaturated compounds for the synthesis of more compounds, particularly plastics.