4.8 Preparation of Alkyl Halides From Alcohols and Hydrogen Halides H.O-H-B Transition state FIGURE 4.6 Energy diagram for concerted bi molecular proton transfer from hydrogen bromide to H,0+ H-Br Reaction coordinate- The molecularity of an elementary step is given by the number of species that undergo a chemical change in that step. The elementary step HBr H0= Br H3o is bimolecular because it involves one molecule of hydrogen bromide and one mole- cule of water PROBLEM 4.11 Represent the structure of the transition state for proton trans- fer from hydrogen chloride to tert-butyl alcohol Proton transfer from hydrogen bromide to water and alcohols ranks among the The 1967 Nobel Prize in most rapid chemical processes and occurs almost as fast as the molecules collide with emistry was shared by one another. Thus the height of the energy barrier separating reactants and products, the Manfred Eigen, a german activation energy for proton transfer, must be quite low. novel methods for measu The concerted nature of proton transfer contributes to its rapid rate. The energy ing the rate cost of breaking the H-Br bond is partially offset by the energy released in making the reactions such as prc H2O-H bond. Thus, the activation energy is far less than it would be for a hypothet ical stepwise process involving an initial, unassisted ionization of the H-Br bond, fol lowed by a combination of the resulting H with water 4. 8 PREPARATION OF ALKYL HALIDES FROM ALCOHOLS AND HY DROGEN HALIDES Much of what organic chemists do is directed toward practical goals. Chemists in the pharmaceutical industry synthesize new compounds as potential drugs for the treatment of disease. Agricultural chemicals designed to increase crop yields include organic com- pounds used for weed control, insecticides, and fungicides. Among the"building block molecules used as starting materials to prepare new substances, alcohols and alkyl halides are especially valuable The procedures to be described in the remainder of this chapter use either an alkane or an alcohol as the starting material for preparing an alkyl halide. By knowing how to Back Forward Main Menu Study Guide ToC Student OLC MHHE WebsiteThe molecularity of an elementary step is given by the number of species that undergo a chemical change in that step. The elementary step HBr H2O BA Br H3O is bimolecular because it involves one molecule of hydrogen bromide and one mole￾cule of water. PROBLEM 4.11 Represent the structure of the transition state for proton trans￾fer from hydrogen chloride to tert-butyl alcohol. Proton transfer from hydrogen bromide to water and alcohols ranks among the most rapid chemical processes and occurs almost as fast as the molecules collide with one another. Thus the height of the energy barrier separating reactants and products, the activation energy for proton transfer, must be quite low. The concerted nature of proton transfer contributes to its rapid rate. The energy cost of breaking the H±Br bond is partially offset by the energy released in making the H2O ±H bond. Thus, the activation energy is far less than it would be for a hypothet￾ical stepwise process involving an initial, unassisted ionization of the H±Br bond, fol￾lowed by a combination of the resulting H with water. 4.8 PREPARATION OF ALKYL HALIDES FROM ALCOHOLS AND HYDROGEN HALIDES Much of what organic chemists do is directed toward practical goals. Chemists in the pharmaceutical industry synthesize new compounds as potential drugs for the treatment of disease. Agricultural chemicals designed to increase crop yields include organic com￾pounds used for weed control, insecticides, and fungicides. Among the “building block” molecules used as starting materials to prepare new substances, alcohols and alkyl halides are especially valuable. The procedures to be described in the remainder of this chapter use either an alkane or an alcohol as the starting material for preparing an alkyl halide. By knowing how to 4.8 Preparation of Alkyl Halides From Alcohols and Hydrogen Halides 137 Potential energy Transition state Reaction coordinate H2O---H---Br H2O  H–Br H3O  Br Eact   The 1967 Nobel Prize in chemistry was shared by Manfred Eigen, a German chemist who developed novel methods for measur￾ing the rates of very fast reactions such as proton transfers. FIGURE 4.6 Energy diagram for concerted bi￾molecular proton transfer from hydrogen bromide to water. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website