Presentation on theme: "7.1 Introduction Reactions of Radicals General reaction."— Presentation transcript:
Reactions of Radicals General reaction
7.2 Homolytic bond dissociation energies 7.2A Homolytic bond dissociation energies and heats of reaction 7.2B Homolytic bond dissociation energies and the relative stabilities of radicals
7.2B Homolytic bond dissociation energies and the relative stabilities of radicals Homolytic bond dissociation energies also provide us with a convenient way to estimate the relative stabilities of radicals.
Relative stabilities of radicals
7.3 The reactions of alkanes with halogens Methane, ethane, and other alkanes react with the first three members of the halogen family: fluorine, chlorine, and bromine. Alkanes do not react appreciably with iodine. With methane the reaction produces a mixture of halomethanes and a hydrogen halide.
Halogenation reactions ( 卤化反应） The reaction of an alkane with a halogen is called halogenation. In these reactions a halogen atom replaces one or more of the hydrogen atoms of the alkane. Reactions of this type, in which one atom or group replaces another, are called substituion reactions
7.9 Reactions that generate tetrahedral stereocenters When achiral molecules react to produce a compound with a single tetrahedral stereocenter, the product will be obtained as a racemic form. Let us examine a reaction that illustrates this principle, the radical chlorination of pentane
The radical chlorination of pentane
How to get (±)-2- Chloropentane ?
7.10 Other important radical chain reactions 7.10A Combustion of alkanes 7.10B Autoxidation 7.10C Freons and ozone depletion( 氟里 昂和臭氧 O 3 的损耗 )
7.10C Freons and ozone depletion( 氟里昂和臭氧 O 3 的损 耗 ) In the stratosphere ( 同温层, 最上层, 最高 阶段 )at altitudes of about 25 km, very high-energy (very short wavelength) UV light converts diatomic oxygen ( O 2 ) into ozone ( O 3 ). The reactions that take place may be represented as follows: