Final_3311f05_key

Final_3311f05_key - CHEM 3311-200, Fall 2005 Final Exam...

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Unformatted text preview: CHEM 3311-200, Fall 2005 Final Exam December 13, 2005 Professor Rebecca Hoenigman I pledge to uphold the CU Honor Code: Signature________________________________________________________ Name (printed)____________________________________________________ Last four digits of your student ID number_______________________________ Recitation TA_____________________________________________________ Recitation number, day, and time______________________________________ You have 2.5 hours to complete this exam. Exams will be collected at 4:00 pm. No model kits or calculators allowed. Periodic table and scratch paper are attached. DO NOT TURN PAGE UNTIL INSTRUCTED TO DO SO. Put your name on ALL pages of the exam Recitation Sections: Number Day Time TA 211 Monday 8 am Kate 251 Monday 2 pm Kate 291 Monday 5 pm Xin 252 Tuesday 12 pm Matt 293 Tuesday 5 pm Jon 212 Wednesday 8 am Greg 253 Wednesday 1 pm Greg 292 Wednesday 5 pm Jon 213 Friday 8 am Xin Average Score = 158 High Score = 276 Low Score = 20 Name: _________________________________ 2 1. (5 pts) Draw the structure of anthracene. 2. (4 pts) Explain why cyclobutadiene is better represented as a rectangle, rather than a square. In a square all the carbon-carbon bond lengths will be equal, and the pi bonds will be delocalized. With 4n pi electrons, cyclobutadiene is antiaromatic and destabilized by electron delocalization. The rectangular geometry limits the interactions of the pi bonds and reduces electron delocalization. 3. (6 pts) In class, we used heats of hydrogenation to explain the stability of dienes. Another way in which energies of isomers may be compared is by their heats of combustion ( H comb ). Match the H comb values given below with the appropriate isomer by writing the H comb value on the line next to the diene name. H comb = 3186 kJ/mol, 3217 kJ/mol, 3251 kJ/mol (2 pts each) 1,2-pentadiene: H comb = ___ 3251 kJ/mol __ ( E )-1,3-pentadiene: H comb = ___ 3186 kJ/mol __ 1,4-pentadiene: H comb = ___ 3217 kJ/mol __ Name: _________________________________ 2 1. (5 pts) Draw the structure of anthracene. 2. (4 pts) Explain why cyclobutadiene is better represented as a rectangle, rather than a square. In a square all the carbon-carbon bond lengths will be equal, and the pi bonds will be delocalized. With 4n pi electrons, cyclobutadiene is antiaromatic and destabilized by electron delocalization. The rectangular geometry limits the interactions of the pi bonds and reduces electron delocalization....
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Final_3311f05_key - CHEM 3311-200, Fall 2005 Final Exam...

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