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Properties and Reactions of Hydrocarbons

Properties and Reactions of Hydrocarbons. Properties of Hydrocarbons. Made up of mostly C and H Relatively nonpolar Low solubility in polar solvents (e.g. water) Good solvents for other nonpolar molecules Mostly london -dispersion forces (weak) Low boiling and melting points.

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Properties and Reactions of Hydrocarbons

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  1. Properties and Reactions of Hydrocarbons

  2. Properties of Hydrocarbons • Made up of mostly C and H • Relatively nonpolar • Low solubility in polar solvents (e.g. water) • Good solvents for other nonpolar molecules • Mostly london-dispersion forces (weak) • Low boiling and melting points

  3. Reactivity of Hydrocarbons • Alkanes are generally less reactive than alkenes or alkynes • Aromatic compounds are more reactive than alkanes, but less reactive than alkenes and alkynes. Alkanes < aromatics < alkenes < alkynes

  4. Reactions of Alkanes • Single bonds between carbon atoms are difficult to break. (This is why alkanes are relatively unreactive) • Can undergo combustion reactions

  5. Reactions of Hydrocarbons Combustion: • Hydrocarbons burn readily in air to produce carbon dioxide and water. Incomplete Combustion: • Produces carbon and poisonous carbon monoxide. C3H8(g) + 5 O2(g) --> 3CO2(g) + H2O(g) C3H8(g) + 7/2 O2(g) --> C(s) + CO(g) CO2(g) + 4 H2O(g)

  6. Reactions of Alkanes Substitution Reactions: • Hydrogen atoms may be substituted by a halogen. • The product is a halogenated alkane (alkyl halides)

  7. Reactions of Alkenes and Alkynes Addition Reactions: • Reactions in which a molecule is added to a double or triple bond (by breaking it). • No loss of hydrogen atoms from the hydrocarbon

  8. Addition Reactions: 1) Hydrogenation 2) Halogenation

  9. Addition Reactions: 3) Hydrohalogenation 4) Hydration

  10. Markovnikov’s Rule • When molecules with two identical atoms (e.g. H2) are added to a double bond, only one possible product is formed. • When molecules of nonidentical atoms (e.g. HBr) are added, two different products are theoretically possible

  11. Markovnikov’s Rule • However, experiments show that only one main product is formed. • This product can be predicted by Markovnikov’s rule • “The rich get richer” • When a hydrogen halide is added to an alkene or alkyne, the hydrogen atom bonds to the carbon atom that already has more hydrogen atoms.

  12. Benzene • Does not act as 3 single bonds and 3 double bonds • It’s 6 identical bonds of intermediate length • Due to hybridization (delocalized, shared electrons)

  13. Reactions of Aromatic Hydrocarbons (Benzene) • Less reactive than alkenes and do not undergo addition reactions unless under conditions of extreme temperature or pressure • Do undergo substitution reactions (more reactive than alkanes)

  14. Organic Halides Properties • Halogen makes the molecule more polar, increasing strength of the intermolecular forces • Higher boiling points than their corresponding hydrocarbons • More soluble in polar solvents • Molecules with more halogens are more polar

  15. Preparing Organic Halides Recall:Substitution reaction produce halides in alkanes and aromatic hydrocarbons

  16. Preparing Organic Halides Recall: alkyl halides are produced in halogenation reactions (addition) with alkenes/alkynes

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