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Organic Chemistry I
Midterm Exam 3
Take-Home Exam: Due
May 5, 2015 at 5:15 pm
1. Make sure there are 8numbered
pages and 9questions to this exam. 2.Printyour
name(last name, first name) on this page of the exam only. 3. Sign your
name below acknowledging that you will honor the pledge and the terms of this
take-home exam. 4. Read each question carefully. Mark your answers concisely
and legibly and show all your work where required in order to receive
partial credit; however, write the answer only in the space
provided. You may use the back of each page as scratch paper, but it will not
be graded. 5. VERY IMPORTANT: This is a take- home exam.
Accordingly, you are permitted to use your textbook, class notes, handouts,
calculator, molecular models and other resources for this exam only. However,
you MUST work alone, and your answers must represent entirely your own efforts.
You may not collaborate, work with, or discuss the questions with anyone.
Pledge:On my honor, I
will not receive or give aid on this examination.
says, "The following information may be useful":
and Double Bonds/Double Bond Equivalents (DBE) formula:
R = (n+1) - [(x-t)/2] where n = number of carbon atoms; x = number of (hydrogen
+ halogen) atoms; t = number of nitrogen atoms.
Electronegativity values: H (2.1), C (2.5), N (3.0), O (3.5), F (4.0), Cl
(3.0), Br (2.8), I (2.5).
A values: CH3 (Me) = 1.74;
Cl = 0.55; Br = 0.48
01. For each pair of compounds, circle the one
that is predicted to be the stronger acid (i.e., lower pKa). The protons
to be compared (H ) are shown in bold type. HINT:
Exam the anions (i.e., conjugate bases in each pair of compounds) and compare
their relative stabilities. (20 pts)
CH3CO2H vs. HF
CH2ClCO2H vs CH2FCO2H
d. CH3OH vs
CH4 vs NH3
f. CF3CH2OH vs CH3CO2H
OH OH vs
CH3SO3H vs CH3CO2H
HCN (i.e, hydrogen cyanide) vs HCCH
(i.e., acetylene or ethyne)
02. Of the following statements,
which are true for nucleophilic substitutions occurring by the SN2
mechanism? Write T or F below each statement. (10 pts)
Primary alkyl halides react faster than secondary.
The absolute configuration of the
product is opposite to that of the reactant if an optically active substrate is
The intermolecular reaction shows second order
d. The rate of the
reaction depends on the nucleophilicity of the attacking nucleophile.
The probable mechanism involves only one step.
g. The rate of the
reaction does not depend on the nature of the leaving group.
h. The rate is
usually faster in polar, protic solvents.
Branching at the?-carbon
has little or no effect on the rate of the reaction.
Hyperconjugation is mainly responsible for
stabilizing the intermediate.
03. Give the expected major product or
products in each of the following transformations. Clearly show stereochemistry
where appropriate (e.g., by using wedged or dashed bond lines, or by writing
axial or equitorial bonds).If no reaction is expected, write “NR”. (40
H H NaI (excess)
F Cl acetone
MeCl CH3OH, 50 °C
NaI (1 molar equivalent)
04. Answer the
following questions concerning nuclephilic substitution reactions.
(a) For each of
the following pairs of reactions, circle the one that is expected to be faster.
(b) For each reaction below, write above
the arrow whether the mechanism follows SN1 or SN2 (03 pts) Then below
each arrow indicate the molecularity of each process. (03 pts)
(CH ) NH+
05. When the deuterium-labeled compound shown
below is subjected to elimination (E2) with sodium methoxide (a strong base),
the only product obtained is 1- deuterio- 3-methycyclohexene (deuterium is an
isotope of H). (a) Justify your answer for this result by drawing structures
and mechanims (electron-pushing arrow formalism). (10 pts). HINT: Start by first
drawing the starting material in the most stable chair conformation.
H3CD CH3O- H3CD
(a) Circle the compound below that reacts faster by the SN2
mechanism. (10 pts) (b) Draw chair cyclohexane structures for the nucleophilic
attack to justify your choice. (10 pts)
07. In the potential energy (PE)/reaction
coordinate (RC) template below, label the indicated parts for a substitution
reaction that occurs by the SN1 mechanism. If there are none of the requested
features, then state “none”. (10 pts)
1. Substrate (S)
and reaction product (P).
state for a unimolecular process.
energy for the rate determining step.
each compound below as polar protic, or polar aprotic. (05 pts)
b. 2-Butanol, CH3CH2CH(OH)CH3
Dimethylsulfide (DMS), CH3SCH3
Hexamethylphosphoric triamide (HMPT), [(CH3)2N]3P=O
09. Characterize each of the
following alcohols, amines, and thiols as being primary (1°), secondary (2°),
or tertiary (3°). (05 pts)
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