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Advanced Higher Chemistry Unit 3 Ethers

Advanced Higher Chemistry Unit 3 Ethers. Ethers. Formula R-O-R ` If R and R` are the same the ether is ‘symmetrical’. If not then it’s unsymmetrical (or asymmetrical). Naming of Ethers. Described as alkoxy substituted alkanes. If unsymmetrical larger alkyl group provides base name.

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Advanced Higher Chemistry Unit 3 Ethers

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  1. Advanced Higher Chemistry Unit 3 Ethers

  2. Ethers • Formula R-O-R` • If R and R` are the same the ether is ‘symmetrical’. • If not then it’s unsymmetrical (or asymmetrical)

  3. Naming of Ethers • Described as alkoxy substituted alkanes. • If unsymmetrical larger alkyl group provides base name. C2H5-O-C2H5 CH3-O-C3H7 CH3-O-C(CH3)3 The most common ether and is frequently just called ‘ether’ ethoxyethane methoxypropane 2-methoxy-2-methylpropane

  4. No hydrogen bonding. • Low boiling points compared to isomeric alcohols • Molecules are polar as C-O bonds are polar and the molecules are non-linear.

  5. Polarity not strong enough to affect boiling points. • Polarity DOES affect solubility in water – hydrogen bonds can form between water and ether molecules • Low formula mass ethers are reasonably soluble in water.

  6. Bonding in Ethers • All bonds in ethers are sigma bonds (see Bonding in Alkanes).

  7. Synthesis of Ethers • Nucleophilic substitution of a halogenalkane by sodium alkoxides (see Halogenalkanes – Synthesis of Ethers) Step 1: R-OH + Na  RO-Na+ + ½ H2 Step 2: RO-Na+ + R`-X  R-O-R` + NaX • This has the advantage over other methods in that it is possible to produce both symmetrical and unsymmetrical ethers with equal ease.

  8. Ethoxyethane is famous as one of the earliest used general anaesthetics but it has been superseded by safer alternatives. • Major use of ethers is as solvents due to: - the polarity of their molecules. This allows a wide variety of organic compounds to dissolve - being relatively unreactive. They are not polar enough to be susceptible to electrophilic or nucleophilic attack and they are resistant to oxidation and reduction. - being easily removed by distillation. Ethers of low formula mass are volatile.

  9. Dangers of ethers • High volatility of simple ethers is coupled with high flammability. • If exposed to air and sunlight they have a tendency to slowly produce unstable peroxides (R-O-O-R) which can be explosive especially towards the end of distillations. • Ethoxyethane evaporates very easily and the vapour formed is much denser than air so can gather in unseen pockets such as sinks. A naked flame or spark is enough to cause a fire or explosion.

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