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Unformatted text preview: Form 0 CHE321 Exam 1 9/26/2006 Multiple Choice Questions. 60 points 1. Draw the two best contributing structures for methylimidate. To get you started a partial structure is given. H C O NH CH 3 H C O NH CH 3 H C O NH CH 3 Choose the incorrect statement. (A) Both contributing structures have the same number of electrons. (B) Both contributing structure have exactly the same geometry. (C) One of the contributing structures has a negative charge on the nitrogen atom. (D) One of the contributing structures has a positive charge on the oxygen atom. (E) A double bond exists between the carbon and nitrogen atoms in both structures. analysis: This question requires you know how to draw different electron configurations (contributing structures or resonance structures) of a given molecule. This topic was discussed in the lecture and was part of quizzes and workshop problems. Scores for this question were high, 72% correct. 2. The carbon frame work of the molecule adamantane, C 10 H 16 , is shown below. adamantane Br Br Choose the correct number of bromoadamatanes (C 10 H 15 Br) that are possible. (A) 1 (B) 2 (C) 3 (D) 4 (E) 5 analysis: This is a difficult problem if you had not done part 3 of workshop 2. Adamantane is a very symmetrical structure and there are only two different hydrogen atoms. Performance on this question was the poorest for all of the multiple choice questions, 26% correct. Form 0 3. From a consideration of the molecular orbital treatment of the hydrogen molecule, choose from the following statement that is incorrect . (A) The molecular orbitals are formed from combinations of the 1s orbitals from each of the two hydrogen atoms. (B) The lower molecular orbital is a (sigma) bonding orbital. (C) The higher molecular orbital is a (sigma*) antibonding orbital. (D) Each of the two molecular orbitals will be occupied electrons fifty percent of the time. (E) The electron density on each of the two hydrogen atoms is equal. analysis: This question requires just a general understanding of molecular orbital theory and orbitals. Molecular orbital theory will be used throughout the course to help us understand certain chemical phenomena. 68% of the students got this question correct. 4. Estimate the equilibrium constant for the following transformation. NH 2 NH 2 G = - RT ln K eq = - 5.72 kJ mol-1 log K eq (at room temperature) (A) 0.01 (B) 0.1 (C) 1 (D) 10 (E) 100 analysis: There is an intimate relationship between changes in molecular structure (organic reactivity) with energy. A qualitative understanding of this logarithimic relationship will assist in understanding why small changes in structure can result in huge changes in reaction rates and equilibria. This subject was part of a in class quiz. 66% of the class got this question correct. 66% of the class got this question correct....
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This note was uploaded on 09/30/2011 for the course CH 310n taught by Professor Iverson during the Spring '08 term at University of Texas at Austin.
- Spring '08