Reference: McMurry Ch 8 George et al Ch 2.2 – 2.4

Alcohols: Rules for naming alcohols follow the guidelines already given for alkanes, in summary

• The number of carbon atoms in the longest carbon chain containing the OH group gives the stem
• Use a prefix to identify the position of the carbon carrying the OH and a suffix of -ol. Number from the end of the chain closest to the alcohol group
• Use numbers and di-, tri- etc as appropriate
• If a molecule contains a multiple bond as well as an alcohol group, give the carbon with the OH group attached the lowest possible number
• Alcohols may be classified as primary (1° ), secondary (2° ), tertiary (3° ) depending on whether the carbon atom carrying the OH is attached to 1 other carbon group, 2 other carbon groups or 3 other carbon groups respectively.

Ethers: Two ways of naming ethers

• The alkyl (or aryl) groups attached to the -O- are named in alphabetical order as two separate words and the word ether added.
• If both of the groups attached to the ether oxygen are the same, the ether name is simplified by using the prefix "di-" with the name of the group e.g. CH₃OCH₃ is called dimethyl ether.
• Alternatively, ethers may be named as alkoxy derivatives of alkanes. In this method of naming, the longest continuous alkyl chain forms the stem of the ether name and the alkoxy group is named as a substituent on the alkane backbone.

• The oxygen atom of an alcohol is sp³ hybridised and has two non bonding pairs of electrons  
• The O-H bond of alcohols is strongly polarised and hydrogen bonding occurs in much the same way as in water molecules
• As a consequence, alcohols have relatively high boiling points compared to other organic compounds of a similar molecular weight and alcohols (particularly the lower members of the series) are significantly more water soluble than other classes of organic compounds which are not capable of hydrogen bonding

• Phenol also shows hydrogen bonding and is partially soluble in water. However ethers are not hydrogen bond donors and so are not soluble in water

• Alcohols absorb radiation strongly ~ 3500 cm^-1 in the infrared region

1. Acid-base reaction of alcohols and phenol

• Alcohols are very weak acids (somewhat weaker than water) but may loose H⁺ from the OH group if sodium or a sufficiently strong base is present
• Phenol is more acidic than alcohols and H⁺ may be removed with sodium hydroxide solution. It is less acidic than carboxylic acids.

Example:

2. Oxidation of alcohols

• Alcohols are oxidised by a variety of oxidising agents, e.g. potassium permanganate in either acidic or basic solution (KMnO₄/H⁺ or KMnO₄/OH^–) or potassium dichromate in acidic solution (K₂Cr₂O₇/H⁺).
• The product of alcohol oxidation depends on whether the starting alcohol is a primary, secondary or tertiary alcohol.
• Oxidation of methanol is unique amongst alcohols as the eventual products of methanol oxidation are water and carbon dioxide.

3. Nucleophilic substitution of alcohols

• Concentrated HX acids (X = Cl, Br, or I) directly convert alcohols to alkyl halides
• The reaction takes place in two steps: protonation followed by substitution
• Protonation converts the R-OH group to R-OH₂⁺ which can then loose H2O
• Substitution of the halide ion for the protonated -OH group affords an alkyl halide

4. Elimination of water from alcohols

Alcohols can also undergo an elimination reaction to form an alkene. H₂O is eliminated from the alcohol so the reaction is also called a dehydration reaction

• This requires a dehydrating reagent, typically concentrated H₂SO₄
• The OH is removed and a hydrogen from the adjacent carbon atom
• Where there is a choice of hydrogens that can be eliminated, the one that results in the most substituted alkene is removed

 Example:

5 ETHERS

Ethers tend to be unreactive and consequently make good solvents.

Questions on Alcohols

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