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Solutions to Problems 49 20. (a) Two: 1-halobutane and 2-halobutane (b) Three (see solution to Problem 21) (c) Four (see solution to Problem 21) (d) Four: X CH₃ CH₃ CH₃ X X (Halomethyl)- 1-Halo-1-methyl- 1-Halo-2-methyl- 1-Halo-3-methyl- cyclopentane cyclopentane cyclopentane cyclopentane 21 (a) (i) (1-chloropentane), CH₃CH₂CH₂CHCICH₃ (2-chloropentane), and CH₃CH₂CHCICH₂CH₃ (3-chloropentane). (ii) (1-chloro-3-methylpentane), (2-chloro-3-methylpentane), (3-chloro-3-methylpentane), and [3-(chloromethyl)pentane]. (b) To answer this question, you first have to count up and identify by type (1°, 2°, or 3°) all the hydrogens whose removal could lead to each one of the products. Then multiply the number of hydrogens you counted by the relative reactivity for that type of hydrogen in a chlorination reaction at 25°C, the conditions for the reaction stated in the problem. This procedure gives you the relative amount of product corresponding to removal of those hydrogens. After you have done this for all the products, you convert these relative amounts into percentage yields by normalizing to 100% (as shown below). (i) 1-Chloropentane is formed by chlorination of any of the six primary hydrogens (each with a relative reactivity = 1) on carbons 1 and 5; its relative yield is 6 X 1 = 6. 2-Chloropentane is formed by chlorination of any of the four secondary hydrogens (each with a relative reactivity = 4) on carbons 2 and 4; its relative yield is 4 X 4 = 16. 3-Chloropentane is formed by chlorination of any of the two secondary hydrogens (each with a relative reactivity = 4) on carbon 3; its relative yield is 2 X 4 = 8. The absolute % yield for each product is calculated as follows: Relative yield of the product X 100% = % yield of that product Sum of relative yields for all products So, Yield of 100% X 6/(6 + 16 + 8) = 100% X 6/30 = 20% Yield of 2-chloropentane = 100% X 16/30 = 53% Yield of 3-chloropentane = 100% X 8/30 = 27% (ii) is formed by chlorination of any of the six primary hydrogens (relative reactivity = 1) on carbons 1 and 5; its relative yield is 6 X 1 = 6. 2-Chloro- 3-methylpentane is formed by chlorination of any of the four secondary hydrogens (relative reactivity = 4) on carbons 2 and 4; its relative yield is 4 X 4 = 16. 3-Chloro-3-methylpentane is formed by chlorination of the single tertiary hydrogen (relative reactivity = 5) on carbon 3; its relative yield is = 5. is formed by chlorination of any of the three primary hydrogens (relative reactivity = 1) on the methyl group attached to carbon 3; its relative yield is X 3 = 3.