Download Solution Key - Chemistry With BT

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ORGANIC CHEMISTRY I (CHEM 323)
EXAM 2
October 27, 2015
There are six pages, NINE questions, and a total of 113 points in this exam,
which gives 13 extra points on top of that required for a “perfect” paper.
Please read each question carefully and possibly more than once. Good luck…
(10)
1.
Complete the following reaction by providing the structure of the major product using a similar template as
the organic reactant. Show the distinguishing feature(s) of the chiral center(s) using dashes and wedges.
1.1.
Identify the stereogenic center(s) in the product using R/S representations.
(10)
2.
The reaction coordinate of the following reaction is given below:
2.1.
Provide a structure for “C” as shown in the reaction
profile.
2.2.
How many stereoisomers of “E” are expected?
2
2.3.
How would you classify the product in terms of its
functional group?
ester
(19)
3.
The reaction below shows the photobromination of 1,2-diphenylethane under uv light (sun light). Only one
stereoisomer of the product is obtained.
Inspired by question from Maria and Chasity
3.1.
How many chiral centers are there in the product (1,2-dibromo-1,2-diphenylethane)?
two
3.2.
3.3.
Generally what is the maximum number of stereoisomers in a compound with the number of chiral
centers you have indicated in question 3.1?
four
Is the stereoisomer obtained in the reaction above optically active? Explain.
No, it is not possible to obtain a chiral product from an achiral reactant
unless chiral reaction conditions are utilized, such as enzyme catalysis
3.4.
Draw a three-dimensional representation of the stereoisomer obtained in the reaction (with wedged
and dashed bonds where appropriate). Assign R and/or S representations for the each of the chiral
centers.
3.5.
Show the homolysis of the bromine molecule using curly arrows
(9)
4.
Outline the multi-step synthesis below. Show any intermediate products formed as well as all the reagents
used.
Page 2
(12)
5.
The acyl group, given in the box in its generic form can be utilized as a leaving group.
5.1.
On the basis of the pKa values of the following acids, choose a leaving group and write the
structure of the compound which would undergo an S N2 reaction most readily.
5.2.
To complete the SN2 reaction, now choose the strongest nucleophile out of the alcohols given
below or one of their conjugate bases.
5.3.
Provide a structure for product of the SN2 reaction between the compound in 5.1 and the
nucleophile in 5.2.
Page 3
Question submitted by Hyo
(14)
6.
Out of the substituted cyclohexyl halides below
6.1.
Identify the one which cannot undergo an E2 reaction (give the letter corresponding to the
structure). C
Explain your reasoning (you may wish to draw a conformation with the requirements of an E2
reaction)
There are no -hydrogens anti- to the leaving group
6.2.
Identify the one which undergoes an E2 reaction the fastest (give the letter corresponding to the
structure). D
Explain your reasoning (you may wish to refer to the factors stabilizing the transition state)
The transition state resembles a tetra-substituted alkene (the most stable); therefore the Ea is the
lowest and the rate of the reaction is the fastest
(10)
7.
Complete the following reactions:
7.1.
7.2.
Page 4
(21)
8.
Circle the best possible correct answer (only one) for the following multiple-choice questions:
8.1.
Enantiomers can be converted into each other by
(1) Free rotation
(2) Dissolving followed by recrystallization
(3) Vaporizing
(4) Plane polarized light
(5) None of the methods mentioned here will convert enantiomers into each other
8.2.
A molecule which is non-superimposable on its mirror image
(1) will rotate plane polarized light
(3) will always be biologically active
(2) has a plane of symmetry
(4) must have more than one chiral center
8.3.
Which one of the carbocationic species given below is the most unstable?
8.4.
Which following pair may have different boiling points?
(1) (A) and (B)
(2) (C) and (D)
(4) They all have different boiling points
(5) They all have the same boiling point
8.5.
(3) (B) and (C)
In the molecule, whose structure is shown, which is the correct interaction for
hyperconjugation (if any)?
(1) Interaction between the sp3 orbital of the carbocation center and the s- orbital of the
hydrogens.
(2) Interaction between the p-orbital of the carbocation center and the s- orbital of the hydrogens.
(3) Interaction between the sp2 orbital of the carbocation center and the s- orbital of the
hydrogens.
(4) Interaction between the p-orbital of the carbocation center and the C-H -orbitals of methyl
(5) Ethyl carbocations do not undergo hyperconjugation.
Page 5
(8)
9.
What is the relationship between the two molecules whose Newman Projection representations are shown
below?
Diastereomers
9.1.
One of the molecules undergoes a reaction with DBU to give the specific stereoisomer below:
Using one of the Newman projection representations above (the correct one!) draw a conformation
which resembles the transition state for the reaction.
The structure of DBU is given below:
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