=========================preview======================
(chem101)[2009](f)midterm~plliu^_10034.pdf
Back to CHEM101 Login to download
======================================================


CHEMISTRY 101: FUNDAMENTALS OF ORGANIC CHEMISTRY

Mid-Semester Examination October 2009
Friday October 23 6:00-8:00 pm
Answer Key
Rooms 3007 and 3008


Time allowed: 120 minutes
Instructions:
i. Write your name and ID number on the examination booklet. If you use more than one examination booklet, be sure to enter your name and ID number on all booklets.
ii. Read the questions carefully. If you get stuck on a problem, go on to the next question.
iii. Write on all pages of your answer booklet. If you use a section for rough work cross it out, and mark as 'rough work'.
iv. Please take care in writing out your answers to the questions. Where stereochemistry is required, take care to draw structures which are comprehensible, and are compatible with the appropriate bond angles
v. There are a total of 120 marks. You have 120 minutes for this exam paper.





DO NOT OPEN THIS EXAMINATION QUESTION BOOKLET UNTIL YOU ARE INSTRUCTED TO DO SO.

1. Consider the structures of the ions 1a-1d and radical 1e below. Each of these may have one or more resonance contributors. All of the attached atoms, including hydrogen atoms are shown in the structures.

a. Redraw the structures in your answer booklet (without the brackets), and draw in lone pairs of electrons, and place postive (+) or negative (-) charges or unpaired spin (.) as required immediately next to the appropriate atoms. (10 pts)



Positive, negative charges and electron pairs must be unambiguously located




b. Draw the resonance contributors to the structure of the cation 1a. (2 pts) Electron pairs and positive charges must be clearly shown:






c. For each of the species 1b-1e, draw the structures of what you consider to be two significant resonance contributors among all the possible resonance contributors. (9 pts)




This question is not so easily answered; reasons for 'stabilization' have not been fully explained, so full points were given if resonance contributors are indicated properly. For 1b, most important contributor is i, with ii and iii equivalent canonical forms C this was indicated in lectures; for 1b, i, iii equivalent, probably most important?; 1d, i and iv most important; 1e, i and iv most important.



d. Draw reasonable stereochemical representations for the structures of each of chloroform (trichloromethane, CHCl3), hypochlorous acid (HOCl), methyl nitrate (H3C-O-NO2, (Z)-1,2-dichloro-ethylene [(Z)-ClCH=CHCl], and all cis-1,2,3-trichlorocyclopropane. (10 pts) No need to show lone pairs (not asked), but tetrahedral nature of C in CHCl3 and C in H3C-O-NO2 must be clearly indicated, and geometry is important for HOCl ('bent'), H3C-O-NO2 (H3C-O-N is 'bent', and -ONO2 is trigonal planar), (Z)-ClCH=CHCl C planar, with Cl atoms on 'same side'. If lone pairs are shown, then tetrahedral representations for the 'bent' structures are fully correc