1. When methane is photochlorinated a small amount of ethane is found in the product. Give a full mechanism to account for presence of the ethane.

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1 Chemistry 51 DS Quiz 2 1. When methane is photochlorinated a small amount of ethane is found in the product. Give a full mechanism to account for presence of the ethane. 2. When 2,3-dimethylbutane is monochlorinated what are the products? What is the percent yield of each product? 3. Draw the transition state for the rate determining step in the chlorination of ethane.

2 Sept 15, 1998 Chem 51 DT Quiz 2 Name 1. Write the mechanism for the free radical bromination of methane to yield bromomethane. 2. a)what is the slow step of the chain process? b) Draw the transition state for the slow step. 3. Give two pieces of experimental evidence which support the free radical mechanism of halogenation.

3 September 18 Chemistry 51 DE Quiz 2 1. Use a Newman projection (C3-C4) diagram to show the most stable conformation of 2,5-dimethylhexane. 2. Give the structures of the products and calculate the percent yield of the monochlorination 2,4-dimethylpentane. 3. Provide a synthesis of 2,4-dimethylpentane from alkyl halides having four or fewer carbons.

4 Chemistry 51 Quiz No. 2 Draw a potential energy curve for rotation about the C2-C3 bond of 2,3-dimethylbutane. Use the diagram below. Be sure to clearly show relative energies C rotate the front carbon You are given a mixture of 16 g of methane and 15 g of ethane. ow many moles of each do you have? ow many molecules do you have of each? ow many hydrogen atoms do you have that are part of methane moleules? ow many hydrogen atoms do you have that are part of ethane moleules? If the reactivity of a hydrogen in ethane is 1.0 and in methane 0.50 what are the relative amounts of methyl chloride and ethyl chloride that will be initially formed (mole fractions).

5 Chemistry 51 DS Quiz 2 Sept 15, 1999 What are the products of the following reactions? 1. ethyl bromide Mg dry ether D 2 O 2. excess 2 cyclopentene Pd 3 Using a Newman projection about the C2 - C3 bond, draw the most stable conformation of 2-methylbutane 4. An unknown compound has the formula C a) What information does the formula give you? b) The unknown does not react with 2 and metal catlyst. What does this tell you? c) Upon free radical chlorination only two monochloro products are obtained. Propose a structure.

6 Chemistry 51 DX Quiz 2 Sept 16, 1999 Give synthetic methods to prepare the following compounds. You may start with alkyl halides having no more than four carbons 1. CD where D is deuterium 2. 2,4,4-trimethylpentane 3. Predict the products from the monochlorination of 2,3-dimethylbutane and give their relative percent yield 4.Using a Newman projection about the C2-C3 bond draw the most stable conformation of 2,3-dimethylbutane

7 Chemistry 51 DX Quiz no Using the graph provided below sketch the potential energy curve for rotation about the C2-C3 bond of 2-methylbutane. The starting conformation, 0 degrees rotation, is provided for you below. Be very careful about showing relative energy levels. E What is the major product for 2-methylpropane subjected to monobromination (relative reactivities are 1:80:1200) 3. Consider the following molecules. 2-bromobutane Br Br A B C Which are compounds that may exhibit optical activity in the lab (for which enantiomers may exist)? Answer by letter 4.Compound X is optically active. The pure R form has a specific rotation of +50. What is the expected specific rotation of a mixture formed from 10.0 g of the R form and 20.0 g of the S form?

8 Chemistry 51 Quiz 2 Spring 2002 February 19, Consider rotation about the central C2-C3 bond of 2,3-dimethylbutane. Using either diagram 1 or 2 below show the structure of the lowest energy conformer a) What is the major product for the free radical monochlorination (1:3.8:5) of 2- methylpropane? b) What is the major product for the free radical monobromination (1:82:1600) of 2- methylpropane? c) When free radical monochlorination of 2-methylpropane is done at elevated temperature the product mixture is 25% tertiary and 75% primary alkyl halide. What are the relative reactivities of the primary and tertiary hydrogens at this temperature. 3. Using alcohols having five or fewer carbons and inorganic reagents provide a synthesis of 3-ethylpentane.

9 Chemistry 51 Quiz 3, Spring Define what is meant by the slow step in a reaction mechanism. 2. What is the slow step in the free radical chlorination of ethane? 3. Sketch the three dimensional nature of the transition state for the rate determining step requested above. 4. Compare by means of energy profiles for the rate determining steps of the chlorination and bromination of ethane. 5. In a particular experiment 2 moles of methane and 1 mole of ethane gas were monochlorinated for a short period of time. Assume that the relative reactivities of the hydrogens in methane and ethane are 1.0 and 1.5 respectively what is the expected ratio of chloromethane to chloroethane?

10 Chemistry 51 Quiz 2, Sept An unknown alkane has the formula C In an attempt to determine its structure the unknown compound was subjected to uv induced chlorination. Only one monochloro product was produced. What is the structure of the unknown? 2. Given the Bond Dissociation Energies below draw the energy profile for the following step of the chlorination mechanism. + CL > Cl + Cl C- 104 Cl - Cl 58 C - Cl 84 - Cl Name the following compound. O 2 C C 2 O CO 2 C 2 O

11 Quiz 2 Chemistry 51 For the following monochlorination show all expected products and how much of each should be expected. Cl 2, light 2,2-dimethylbutane For 2,3-dimethylbutane sketch the rotational energy curve around the central C2 - C3 bond. E Use the eclipsed conformation shown below as the zero degree starting point. Be sure to indicate relative energies carefully. C 3 3 C 3 C

12 Chemistry 51 Quiz 2, Sept 17, An unknown compound has the formula C Upon monochlorination followed by careful fractional distillation four fractions were obtained. Propose a structure for the unknown compound. 2. a)subsequent to initiation what is the rate determining step in bromination of methane? b) Make a careful drawing of the transition state for the step in a) above. Be sure to show relative bond strength. 3. For the compound iso butane (2-methylpropane) a) What are the expected products of monochlorination? b) Assuming random replacement of hydrogens what are the expected fractional yields? c) If it is found that two compounds are formed in the amounts of 60.0% and 40.0% what is the most reasonable assignemnt of reactivities for the various types of hydrogens in iso butane?

13 Chemistry 51, Fall 2004 Quiz 2 reactivities: chlorination 1 : 3.8 : 5.0 bromination 1 : 82 : a) What is the overall reaction of ethane and chlorine in the presence of uv light? b) What is the mechanism of the reaction including termination steps? c. Carefully draw the transition states for the chain steps in the mechanism. Be sure to indicate relative bond strengths. 2.An unknown hydrocarbon has the formula C Upone uv induced monochlorination it forms only one monochloroderivative. Suggest a structure. 3. Equimolar amounts of octane and 2,2,4-trimethylpentane are reacted with chlorine in the presence of uv. Which compound is chlorinated faster? Why? What is the relative rates of reaction of the two compounds?

14 Chemistry 51 Spring 2007, Quiz 2, February Complete the diagram below to represent the requested conformations of 3 methylpentane C 2 5 least stable eclipsed conformation most stable staggered conformation 2. Using the axes below draw the rotational profile for rotation about the bond depicted in the conformations above. The starting conformation, 0 degrees, should be the most stable staggered conformation E a) Accurately draw the three dimensional structures of the most stable conformations of cis and trans 4 methyl tert butyl cyclohexane. cis trans b) What is the stability difference between the two structures.