Selected Problems from Past Intra-Term Examinations

CHEMISTRY 281-4 (2012-3). Dr. Pete Wilson

ORGANIC CHEMISTRY I: PROBLEM SET 2.

WEEK 3 – LECTURE 7/8

Selected Problems from Past Intra-Term Examinations

For discussion in tutorials (Week 4) in addition to any other general questions you may have about the course material.

Notes:

Your first intra-term examination will consist of questions that relate to the topics covered in class up to the end of Week 4.

This problem set is representative, if not beyond (because of curriculum changes and that your examination is earlier than in previous years),ofwhat you may expect in your first intra-term examination.

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SIMON FRASER UNIVERSITY

Organic Chemistry I, 2005-3

/ CHEM 281 /

Dr. Peter D. Wilson

INTRA-TERM EXAMINATION 1

(12.5 % of total course evaluation)

10:35 – 11:20 a.m. Wednesday 19, October 2005

Answer all of the questions (8 questions). Your exam consists of 8 printed pages including this one (please check this when you are told to do so). Fill in your name and student number below. The use of a copy of the periodic table, molecular models and an electronic calculator is allowed.

NAME:…………………………………………………………………

STUDENT #:………………………………………………………………….

Marking Scheme

Question MarksScore

410

TOTAL50

TOTAL12.5

1. a). Draw the chemical structures of the three stereoisomers of 1,2-dimethylcyclopropane. You should use wedged and hatched bonds to carefully show the stereochemistry (3 marks).

1. b). One of the structures that you have drawn above represents an achiral compound (a non-chiral meso compound). Draw a circle around this structure (1 mark).

1. c). What is the stereochemical relationship of the other two stereoisomers (i.e. the ones that you have not drawn a circle around) - are they diastereoisomers or enantiomers (1 mark)?

2. Of the following, draw a circle around the chiral molecules (5 marks).

3. Draw the molecular structures of 10 different compounds that have the molecular formula – C6H12. You can include: cyclic and non-cyclic compounds, alkenes (including different E- and Z-isomers), different enantiomers and diastereoisomers of a particular compound (5 marks).

4. Consider the compound ("Peteane") below and answer the following questions. Note; all of the hydrogen atoms are omitted for clarity (10 marks).

4. a). What is the molecular formula of Peteane (1 mark)?

4. b). How many quaternary carbons does Peteane have (1 mark)?

4. c). How many tertiary hydrogens does Peteane have (1 mark)?

4. d). How many primary carbons does Peteane have (1 mark)?

4. e). How many secondary carbons does Peteane have (1 mark)?

4. f). Is Peteane chiral or achiral (non-chiral) (1 mark)?

4. g). Provide the IUPAC name for Peteane (2 marks).

4. h). If Peteane was completely burnt in air (“cremated” - a combustion reaction) what would the products of this reaction be and how many molar equivalents of each product would be produced (2 marks)? Note; an excess of oxygen is involved – you are not being asked to calculate the amount of oxygen involved.

5. Consider the compound below (an isotopically-labeled carboxylic acid) and answer the following questions (6 marks).

5. a). The reaction of the carboxylic acid with sodium hydroxide (NaOH) affords a salt. Draw the chemical structure of this salt (1 mark).

5. b). Now draw the corresponding resonance structure of this salt (1 mark).

5. c). Using “double-headed curly arrows” to illustrate the movement of electrons, show how these two resonance structures interconvert (in part b) (1 mark).

5. d). What is the byproduct of the above reaction (see part a, i.e. what else is produced) (1 mark)?

5. e). If the three deuterium (D) atoms of this compound were replaced with fluorine atoms, would this compound (CF3CO2H) be more or less acidic than the original compound (1 mark)?

5. f). Would the pKa value of CF3CO2H be more or less positive than the original compound (1 mark)?

6. a). By taking a view along the C2-C3 bond of butane (CH3CH2CH2CH3), draw the two energetically different eclipsed and the two different staggered conformations that this molecule can adopt (i.e.draw the Newman projections) (2 marks).

6. b). Based on steric arguments, draw a circle around the most stable conformation that you have drawn above (1 mark).

6. c). Based on steric arguments, draw a box around the least stable conformation that you have drawn above (1 mark).

7. Consider the chiral nonracemic compound ("Donaldane") below and answer the following questions. Donaldane has a melting point of 50 °C and a specific rotation ([]) of + 100 (c 1.0, chloroform). Note, all of the hydrogen atoms are omitted for clarity (9 marks).

7. a). Provide the IUPAC name of Donaldane. You should include R,S assignments and the substituents of the cyclohexane ring should be numbered to give the lowest possible numbering scheme (4 marks).

7. b). Draw the two different chair-like conformations of Donaldane and draw a circle around the most stable conformation (3 marks).

7. c). Draw the chemical structure of the enantiomer of Donaldane (1 mark).

7. d). What would you expect the melting point and specific rotation of the enantiomer of Donaldane (i.e. the compound that you have drawn in part c) to be (1 mark)?

8. Consider the following compound and answer the following questions (6 marks).

8. a). What is the hybridization of atom A (1 mark)?

8. b). What is the hybridization of atom B (1 mark)?

8. c). What is the hybridization of atom C (1 mark)?

8. d). What is the hybridization of atom D (1 mark)?

8. e). The sigma bond between atom A and an attached hydrogen atom is due to the interaction of what types of hybrid and atomic orbitals (1 mark)?

8. f). The pi bond between atoms C and D is due to the interaction of what types of orbitals (1 mark)?

There is no more to do – but do go back and check your answers!

Some Additional Questions:

1. a). Draw the chemical structures of the three stereoisomers of 1,2-dimethylcyclohexane. You should use wedged and hatched bonds to carefully show the stereochemistry (3 marks).

1. b). One of the structures that you have drawn above represents an achiral compound (a meso compound). Draw a circle around this structure (1 mark).

1. c). For one of the other stereoisomers (i.e. not the meso compound), that you have drawn above (inpart a), draw the two chair-like conformations that this stereoisomer can adopt (2 marks).

1. d). One of the conformations that you have drawn above (inpart c) is more stable than the other. Draw a circle around this conformation (1 mark).

2. Consider compound A below and answer the following questions.

2. a). What is the molecular formula of compound A (1 mark)?

2. b). How many quaternary carbon centres does compound A have (1 mark)?

2. c). How many tertiary hydrogens does compound A have (1 mark)?

2. d). Provide the IUPAC name for compound A and include R/S nomenclature. Note: You will need to use the prefix “tetra” somewhere in the compound’s proper name and the numbering system that is provided (4 marks).

3. Consider the following compound and answer the following questions (5 marks).

3. a). Assign the absolute stereochemistry of this compound (i.e. is it R or S) (1 mark).

3. b). The reaction of this compound with sodium hydroxide (NaOH) affords a salt. Draw the chemical structure of this salt (1 mark).

3. c). Now draw the corresponding resonance structure of this salt (1 mark).

3. d). Using “double-headed curly arrows”, show how these two resonance structures inter-convert (in part c) (1 mark).

3. e). What is the byproduct of the above reaction (i.e. what else is produced) (1 mark)?

4. Consider the following compound and answer the following questions (7 marks).

4. a). The carbon-carbon bond (a) is due to the interaction of what type of hybrid atomic orbitals (1 mark)?

4. b). The carbon-carbon sigma bond (b) is due to the interaction of what type of hybrid atomic orbitals (1 mark)?

4. c). The carbon-carbon pi bond (b) is due to the interaction of what type of atomic orbitals (1 mark)?

4. d). The carbon-hydrogen bond (c) is due to the interaction of what type of atomic and hybrid atomic orbitals (1 mark)?

4. e). The carbon-hydrogen bond (d) is due to the interaction of what type of atomic and hybrid atomic orbitals (1 mark)?

4. f). What is the IUPAC name of this compound (you should include in the name a descriptor to account for the geometry of the double bond) (2 marks)?