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Chemistry 2e · Organic Chemistry

Alcohols and Ethers

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Science note: Boiling points (ethanol ≈ 78 °C, dimethyl ether ≈ −24 °C) and standard atomic weights are commonly taught reference values; measured values vary with purity and pressure. Safety statements are general principles only, not procedures.
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On this page 9 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Worked example
  6. Key takeaway
  7. Check yourself
  8. Study tools
  9. Sources & references

In 30 seconds

An alcohol is any organic molecule that carries a (-OH) on a saturated (sp³) carbon, and an is a molecule with an oxygen atom bonded to two carbon groups (R-O-R'). The two families look similar, but that single -OH group changes nearly everything: alcohols hydrogen-bond to one another, while ethers cannot. That difference controls boiling point, water solubility, and reactivity, and it explains why ethanol is a liquid at room temperature while dimethyl ether is a gas. This topic covers how to recognize, name, classify, and predict the behavior of both families.

Why this matters

Alcohols and ethers show up in fuels, solvents, medicines, and everyday products. Ethanol is the alcohol in beverages and a common fuel additive; isopropanol is rubbing alcohol; ethylene glycol is antifreeze; diethyl ether was the first surgical anesthetic. Knowing which family a molecule belongs to lets you predict whether it mixes with water, boils at a useful temperature, or can be oxidized into another compound. In the lab and in industry, mistaking an alcohol for an ether leads to wrong safety assumptions, because the two families differ sharply in toxicity, flammability, and reactivity.

The college version

Core Concepts

The hydroxyl group defines an alcohol

An alcohol has the general formula R-OH, where R is an alkyl group and -OH is the hydroxyl group. The carbon that carries the hydroxyl group fixes the alcohol class: primary (1°) alcohols have -OH on a carbon bonded to one other carbon, secondary (2°) alcohols to two, and tertiary (3°) alcohols to three. Class predicts oxidation behavior and shapes physical properties. Methanol, ethanol, and isopropanol are all small alcohols, but they differ in class and in how the body handles them: methanol is dangerously toxic, while ethanol is tolerated in small amounts.

Naming alcohols and ethers

For alcohols, find the longest continuous carbon chain that includes the -OH carbon, change the alkane ending -e to -ol, and number the chain so the hydroxyl carbon gets the lowest number. Propan-2-ol (2-propanol) therefore names a three-carbon chain with -OH on carbon 2. Ethers use two naming systems: the common name lists the two alkyl groups followed by "ether" (ethyl methyl ether), while the IUPAC system treats the smaller group as an alkoxy prefix attached to the longer alkane (methoxyethane).

Hydrogen bonding sets the physical properties

Alcohols hydrogen-bond through their -OH hydrogen, so their molecules stick together and boil at higher temperatures than alkanes or ethers of similar molar mass. Ethers have no -O-H bond, so ether molecules cannot hydrogen-bond to one another and boil much lower. Both families can hydrogen-bond to water through their oxygen atom, which is why small alcohols and small ethers dissolve in water; solubility falls as the carbon chain lengthens and the nonpolar portion grows.

Alcohols oxidize; ethers mostly do not

Under controlled oxidation, a primary alcohol becomes an aldehyde, which can be oxidized further to a carboxylic acid; a secondary alcohol becomes a ketone; a tertiary alcohol has no hydrogen on its hydroxyl carbon and resists oxidation under ordinary conditions. Ethers lack an -O-H bond and are generally resistant to oxidation, which is why they make stable solvents. The alcohol class therefore predicts the oxidation product, a relationship used constantly in synthesis planning and in exam problems.

Common Confusions

Do Not ConfuseWithDifference
An alcoholAn etherOnly an -OH on carbon makes an alcohol; an ether is R-O-R' with no O–H bond.
1° vs 3° alcohol classificationTotal chain lengthClass comes from carbons attached to the -OH carbon, not from chain length.
Oxidation of a 2° alcoholOxidation of a 1° alcohol2° gives a ketone; 1° gives an aldehyde that can go on to a carboxylic acid.
Ethers dissolving in waterEthers hydrogen-bonding to each otherEthers bond to water through oxygen but cannot bond to one another.
Boiling point by molar massBoiling point by intermolecular forceHydrogen bonding lets an alcohol boil far above an ether of equal molar mass.
Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Alcohols and ethers are two families of molecules that both contain oxygen. An alcohol is like a molecule holding a water-like handle, so the molecules grab each other and stay liquid at room temperature. An ether hides its oxygen between two carbon chains, so the molecules slip past each other and boil much faster. If you know which family a molecule belongs to, you can guess whether it mixes with water and whether heating or oxidizing it makes something new.

Worked examples

Consider 1-propanol and 2-propanol, both C3H8O. The longest chain containing the hydroxyl carbon is propane in each case, so both names end in -ol: the -OH sits on carbon 1 in propan-1-ol and on carbon 2 in propan-2-ol. Classify by counting the carbons bonded to the hydroxyl carbon: in 1-propanol that carbon bonds to one other carbon (1°), while in 2-propanol it bonds to two (2°). Oxidation therefore converts 1-propanol to propanal and then to propanoic acid, but converts 2-propanol only to propanone (acetone). The ether CH3-O-CH2CH3 is ethyl methyl ether by the common system; by IUPAC rules the shorter group becomes the methoxy prefix, giving methoxyethane.

Compare ethanol (C2H5OH) with dimethyl ether (CH3-O-CH3). They share the molecular formula C2H6O, so their molar masses are equal. Write the formula, then substitute the standard atomic weights:

M(C2H6O) = 2(12.01 g/mol) + 6(1.008 g/mol) + 1(16.00 g/mol) = 46.07 g/mol

Because the masses match, the boiling-point gap must come from intermolecular forces: ethanol hydrogen-bonds through its -OH, while dimethyl ether cannot hydrogen-bond to itself. Ethanol boils near 78 °C and is a liquid at room temperature; dimethyl ether boils near -24 °C and is a gas. The lesson: molar mass alone does not predict boiling point, because hydrogen bonding dominates for alcohols.

Key takeaways

  • An alcohol has -OH on a carbon; an ether is R-O-R' with no -O-H bond.
  • Classify alcohols as 1°, 2°, or 3° by counting the carbon atoms bonded to the hydroxyl-bearing carbon.
  • To name an alcohol, find the longest chain containing the -OH carbon, change -e to -ol, and number so that carbon gets the lowest number.
  • Alcohols hydrogen-bond to one another, so they boil higher than ethers or alkanes of similar molar mass.
  • Small alcohols and ethers dissolve in water because both can hydrogen-bond with water.
  • Oxidation: 1° alcohol → aldehyde → carboxylic acid; 2° alcohol → ketone; 3° alcohol resists ordinary oxidation.
  • Methanol and ethylene glycol are toxic; ethanol and isopropanol are familiar everyday alcohols.

Check yourself

5 review questions from the chapter. Try each one, then open the answer.

  1. What structural feature distinguishes an alcohol from an ether?

    Show answer

    An alcohol has a hydroxyl group (-OH) on a carbon; an ether has an oxygen bonded to two carbon groups with no -O-H bond.

  2. How do you classify an alcohol as primary, secondary, or tertiary?

    Show answer

    Count the carbon atoms bonded to the carbon that carries the -OH: one = primary, two = secondary, three = tertiary.

  3. Why does ethanol boil far above dimethyl ether even though both are C2H6O?

    Show answer

    Ethanol hydrogen-bonds through its -OH group; dimethyl ether cannot hydrogen-bond to itself, so it boils much lower despite the same molar mass.

  4. What product forms when a secondary alcohol is oxidized?

    Show answer

    A ketone (for example, 2-propanol → propanone); ketones resist further oxidation under ordinary conditions.

  5. Why do small alcohols and ethers dissolve in water?

    Show answer

    Their oxygen atoms hydrogen-bond with water, so small members of both families mix freely with water.

Keep learning

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Study tools & related lessonsKey vocabulary · Related

Key vocabulary

hydroxyl group
The -OH unit bonded to a carbon atom in an alcohol.
primary (1°) alcohol
An alcohol whose -OH carbon is bonded to one other carbon.
secondary (2°) alcohol
An alcohol whose -OH carbon is bonded to two other carbons.
tertiary (3°) alcohol
An alcohol whose -OH carbon is bonded to three other carbons.
ether
A compound with an oxygen bonded to two carbon groups, R-O-R'.
alkoxy group
The -O-R portion used as a prefix in systematic ether names.
hydrogen bond
A strong dipole attraction between -OH (or -NH) groups.

Sources & references

  1. openstax.org — Chemistry 2e

This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.

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