Grade by Grade
B. Organic Chemistry · Organic Chemistry

Ethers: Naming, Properties and Functional-Group Isomers

B2.2 B3.1 B3.2 B3.3 B3.5About 60 minutes
Learning goals
  • I can name and draw ethers with the IUPAC (alkoxyalkane) system and recognize common names.
  • I can explain how the boiling points and solubility of ethers compare with those of alkanes and alcohols.
  • I can write an equation for making an ether by a condensation reaction of two alcohols.
  • I can draw and name alcohol and ether isomers that share a molecular formula.

Words to know

ether
An organic compound with an oxygen atom bonded to two carbon atoms: R–O–R′.
alkoxy group
An –O–R group named as a substituent, such as methoxy (–OCH₃) or ethoxy (–OCH₂CH₃).
condensation reaction
A reaction in which two molecules join and a small molecule, usually water, is released.
hydrogen-bond acceptor
An atom with a lone pair (such as O or N) that a δ+ H from another molecule can be attracted to.
functional-group isomers
Compounds with the same molecular formula that belong to different families, such as an alcohol and an ether.

An oxygen bridge

On October 16, 1846, in Boston, a patient breathed the vapour of diethyl ether and had a tumour removed from his neck without pain. That public demonstration helped launch general anaesthesia in surgery. Today safer anaesthetics are used, but ethers are still important solvents, fuels and building blocks.

An ether has an oxygen atom bonded to two carbon atoms: R–O–R′ (R and R′ are carbon groups, the same or different). Compare an alcohol, R–O–H, where oxygen is bonded to one carbon and one hydrogen. That single difference, an H on the oxygen or not, changes the properties a lot.

Naming ethers

IUPAC (alkoxyalkane) names. Treat the ether as an alkane with an alkoxy substituent.

  1. The longer carbon group is the parent alkane.
  2. The shorter group plus the O is the substituent: change -yl to -oxy: methyl → methoxy, ethyl → ethoxy, propyl → propoxy.
  3. Give the alkoxy group a locant if needed, and list it alphabetically with any other substituents.

CH₃–O–CH₂CH₃ is methoxyethane. CH₃CH₂–O–CH₂CH₃ is ethoxyethane.

Common names. Name both groups attached to the O, in alphabetical order, followed by ether: CH₃OCH₂CH₃ is ethyl methyl ether; CH₃CH₂OCH₂CH₃ is diethyl ether (the anaesthetic, often just called "ether").

CH₃OCH₂CH₃methoxy-smaller group + Oethanelonger chain = parentmethoxyethane(ethyl methyl ether)
Building an IUPAC ether name. The shorter group and the oxygen become the alkoxy prefix (methoxy-); the longer chain is the parent alkane (ethane).
Worked example

Example 1: Naming ethers

Name (a) CH₃CH₂CH₂OCH₃ and (b) CH₃CH₂OCH(CH₃)₂ with IUPAC and common names.

  1. (a) Groups on O: CH₃ (1 C) and CH₂CH₂CH₃ (3 C). Parent: propane. The methoxy is on C1 of propane.
  2. IUPAC: 1-methoxypropane. Common: methyl propyl ether.
  3. (b) Groups on O: CH₂CH₃ (2 C) and CH(CH₃)₂ (3 C, attached by its middle carbon). Parent: propane, with the ethoxy on C2.
  4. IUPAC: 2-ethoxypropane. Common: ethyl isopropyl ether.

(a) 1-methoxypropane, (b) 2-ethoxypropane.

Worked example

Example 2: Drawing from a name

Draw 2-methoxy-2-methylpropane and give its molecular formula.

  1. Parent: propane, C1–C2–C3.
  2. On C2: a methoxy group (–O–CH₃) and a methyl group (–CH₃).
  3. Condensed: (CH₃)₃C–O–CH₃.
  4. Count: 3 + 1 + 1 = 5 C; 9 + 3 = 12 H; 1 O.

(CH₃)₃COCH₃, C₅H₁₂O. (This compound, known as MTBE, was once added to gasoline.)

Properties of ethers

  • The C–O–C bond angle is about 110°, so the molecule is bent and the two polar C–O bonds give it a small dipole. Ethers have weak dipole-dipole forces plus London forces.
  • An ether has no H bonded to O, so ether molecules cannot hydrogen-bond to each other. Their boiling points are close to those of alkanes of similar mass and far below those of alcohols.
  • But the oxygen's lone pairs can accept a hydrogen bond from water. So small ethers are moderately soluble in water: about 7 g of diethyl ether dissolves in 100 mL of water, about the same as butan-1-ol, its isomer.
  • Ethers are good solvents for many organic compounds and are fairly unreactive, apart from burning.
  • Hazards: diethyl ether is extremely flammable; its vapour is heavier than air and can flow along a bench to a flame. Old containers can form explosive peroxides, so ethers are dated when opened and used up quickly.
0 °C−1 °CbutaneC₄H₁₀, 58 g/mol7 °CmethoxyethaneC₃H₈O, 60 g/mol97 °Cpropan-1-olC₃H₈O, 60 g/molboiling points of molecules with almost the same mass
Methoxyethane and propan-1-ol are isomers with the same mass, but only the alcohol can form hydrogen bonds between its molecules. The ether boils close to butane, an alkane of similar mass.
CH₃OCH₃HOHether + waterH-bondCH₃OCH₃CH₃OCH₃ether + etherno O–H, so no H-bondEthers can ACCEPTa hydrogen bond fromwater, but cannothydrogen-bond toeach other.
Water can donate a hydrogen bond to an ether's oxygen, which is why small ethers dissolve somewhat in water. Two ether molecules cannot hydrogen-bond, because neither has an H on oxygen.

Making ethers: a condensation reaction

Heating a primary alcohol with concentrated sulfuric acid can do two different things, depending on the temperature:

  • At about 140 °C, two alcohol molecules join and lose one water molecule, forming an ether. This is a condensation reaction:

2 CH₃CH₂OH —(H₂SO₄, 140 °C)→ CH₃CH₂–O–CH₂CH₃ + H₂O

  • At about 170 °C, each alcohol molecule loses water on its own, forming an alkene by elimination (Lesson 7):

CH₃CH₂OH —(H₂SO₄, 170 °C)→ CH₂=CH₂ + H₂O

Condensation reactions are important: you will see them again when esters, amides and polymers form.

Worked example

Example 3: Functional-group isomers of C₄H₁₀O

Draw and name all the alcohols and ethers with the formula C₄H₁₀O.

  1. Alcohols (–OH on a C₄ skeleton): butan-1-ol, butan-2-ol, 2-methylpropan-1-ol, 2-methylpropan-2-ol.
  2. Ethers (O between carbons, with 4 C shared out as 1 + 3 or 2 + 2): 1-methoxypropane (CH₃OCH₂CH₂CH₃), 2-methoxypropane (CH₃OCH(CH₃)₂) and ethoxyethane (CH₃CH₂OCH₂CH₃).
  3. Check for repeats by naming each one.

Seven isomers: four alcohols and three ethers. Alcohols and ethers with the same formula are functional-group isomers.

Worked example

Example 4: Predicting a condensation product

What ether forms when methanol is heated with concentrated H₂SO₄ under conditions that favour ether formation? Write the equation.

  1. Two CH₃OH molecules join through one O; one H₂O is released.
  2. Product: CH₃–O–CH₃.

2 CH₃OH → CH₃OCH₃ + H₂O; the product is methoxymethane (dimethyl ether), used as an aerosol propellant.

Hands-on activity

Isomer showdown: C₃H₈O

You need: model pieces (3 "carbon", 1 "oxygen" in a third colour, 8 "hydrogen"), toothpicks, paper. Grown-up note: toothpicks are sharp.

  1. Build every molecule with the formula C₃H₈O. (Hint: there are three.)
  2. Name each one. Classify it as an alcohol or an ether.
  3. Predict which one has the lowest boiling point and explain why.
  4. Check your prediction: the three boiling points are 7 °C, 82 °C and 97 °C. Match them.
  5. Extend: build all seven isomers of C₄H₁₀O (Example 3) and sort them into "can hydrogen-bond to each other" and "cannot".

What to look for: the three C₃H₈O isomers are propan-1-ol (97 °C), propan-2-ol (82 °C) and methoxyethane (7 °C). The ether boils lowest because it cannot hydrogen-bond to itself. Propan-2-ol boils a little lower than propan-1-ol because its –OH is in the middle of a more compact molecule.

Just for fun

Ethers are the introverts of organic chemistry: they can't hydrogen-bond with each other, but they'll happily hydrogen-bond with water, as long as water makes the first move.

Your turn

1

What is the general structure of an ether?

2

Name CH₃OCH₃ (IUPAC and common).

3

Name CH₃CH₂OCH₂CH₂CH₃.

4

Draw (condensed) 2-methoxybutane.

5

Why does methoxyethane boil at 7 °C but its isomer propan-1-ol at 97 °C?

6

Write the equation for forming ethoxyethane from ethanol.

More practice: warm-up

1

What is the name of the –OCH₂CH₃ group?

2

Can ether molecules hydrogen-bond to each other?

3

What small molecule is released when two alcohols condense into an ether?

4

Give the common name of ethoxyethane.

5

Are alcohols and ethers with the same formula isomers?

More practice: on your own

1

Name (CH₃)₂CHOCH(CH₃)₂.

2

Which is more soluble in water: ethoxyethane or pentane? Explain.

3

Rank by boiling point: methoxyethane, ethanol, propane. Explain.

4

Why must a lab bottle of diethyl ether be dated when it is opened?

5

Heating ethanol with H₂SO₄ gives a gas at 170 °C but a volatile liquid at 140 °C. Identify each product and reaction type.

Challenge

1

Heating a mixture of methanol and ethanol with H₂SO₄ under ether-forming conditions gives three ethers. Name them and explain why.

2

Diethyl ether (74 g/mol) and butan-1-ol (74 g/mol) dissolve in water to about the same extent, yet their boiling points are 35 °C and 118 °C. Explain both facts.

3

A C₄H₁₀O compound does not react with sodium metal (alcohols do, releasing H₂) and boils at 39 °C. Which isomers are possible, and which data would decide between them?

Check your understanding

Quiz

1.

What is the IUPAC name of CH₃OCH₂CH₂CH₃?

2.

Why do ethers have much lower boiling points than alcohols of similar mass?

3.

Which pair are functional-group isomers?

4.

What type of reaction forms an ether from two alcohol molecules?

5.

What is a major hazard of diethyl ether?

6.

How many C₄H₁₀O isomers are ethers?

For parents and teachers

Big ideas (B2.2, B3.2, B3.5): ethers (R–O–R′) are named as alkoxyalkanes. With no O–H they cannot hydrogen-bond to each other, so they boil like alkanes, but they accept hydrogen bonds from water. They form by condensation of alcohols and are functional-group isomers of alcohols.

How to help: Write a formula such as C₃H₈O and ask your teen for all the isomers, which families they belong to, and which boils lowest.

Common difficulties:

  • Choosing the longer group as the alkoxy prefix (it should be the shorter one).
  • Thinking ethers hydrogen-bond like alcohols.
  • Mixing up condensation (two molecules join, lose water) and elimination (one molecule loses water, forms C=C).

Safety: ethers are lab chemicals only; this lesson's activity uses models.