Angle strain epoxides

Thus epoxides like cyclopropanes have significant angle strain They tend to undergo reactions that open the three membered nng by cleaving one of the carbon-oxygen bonds... 

Angle strain is the main source of strain in epoxides but torsional strain that re suits from the eclipsing of bonds on adjacent carbons is also present Both kinds of strain are relieved when a ring opening reaction occurs... 

The most striking chemical property of epoxides is their far greater reactivity toward nude ophilic reagents compared with that of simple ethers Epoxides react rapidly with nude ophiles under conditions in which other ethers are inert This enhanced reactivity results from the angle strain of epoxides Reactions that open the nng relieve this strain... 

The one general exception to the rule that ethers don t typically undergo Sn2 reactions occurs with epoxides, the three-membered cyclic ethers that we saw in Section 7.8. Epoxides, because of the angle strain in the three-membered ring, are much more reactive than other ethers. They react with aqueous acid to give 1,2-diols, as we saw in Section 7.8, and they react readily with many other nucleophiles as well. Propene oxide, for instance, reacts with HC1 to give l-chloro-2-propanol by Snj2 backside attack on the less hindered primary carbon atom. We ll look at the process in more detail in Section 18.6. 

The bond angle around the O atom in an alcohol or ether is similar to the tetrahedral bond angle of 109.5°. In contrast, the C-O-C bond angle of an epoxide must be 60°, a considerable deviation from the tetrahedral bond angle. For this reason, epoxides have angle strain, making them much more reactive than other ethers. 

You might also recall from Section 12.7 that epoxides, cyclic ethers with a three-memhered ring, are unusually reactive in Sn2 processes because of angle strain. Methylenecyclohexane oxide, for instance, undergoes a base-induced Sn2 ring-opening on treatment with hydroxide ion at 100 °C. 

Epoxides are more reactive than acyclic ethers because of the angle strain in the three-membered ring. Thus, they readily undergo substitution reactions whether or not they are activated by protonation. 

Epoxides may be readily opened in 8 2 processes to give, after work-up, alcohols. The reaction is favorable because of the release of angle strain in the epoxide. In a simple example (Figure 9.18), a trans but racemic product is obtained (the starting material is not chiral and... 

Figure 7.4 Metabolic oxidation of naphthaiene forms an intermediate 1,2-arene oxide. This has oniy one aromatic ring as compared to naphthaiene, which has two.The epoxide ring has abnormaiiy smaii bond angies which produces significant small-angle strain energy. Arene oxides usuaiiy undergo further chemical changes that result in opening of the smaii ring.

Epoxides are cylic ethers which are highly reactive because of the strained bond angles of a three-membered ring. Because of the high reactivity of epoxides, they are the starting materials for so-called epoxy resins used for high-strength adhesives. 

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