Chemistry 211
Fall 2008
Equilibrium Controlled Reactions:
Carbonyl Reactions - 1
A. Introduction and Review of Equilibrium Controlled Reactions
(See the 10 examples in Summary of Class Discussion of the Introduction to Reactions Activity)
Recall that in the Introduction to Organic Reactions Activity we classified the original example reactions as Simple or Complex reactions and as
Additions, Substitutions, Eliminations or Acid-Base (H-transfer) Reactions. We discovered that the simplest reactions of carbonyl compounds were
proton transfer (Acid-Base) reactions, which occur by an unambiguous single step reaction. We examined lots of data on these simple (Acid-Base)
reactions to try to understand why reactions occur. We discovered that equilibrium controlled reactions proceed in the direction of the lower
energy species. Further, we discovered that we could predict relative energies of structures by estimating the energies of their highest energy e-'s
(HEE's).
B. Complex Equilibrium Controlled Reactions: With the experience we have from Acid-Base reactions, we are prepared to go back and look at the
complex reactions to see if we can understand how and why they occur. Consequently, those reactions are reproduced below as they were analyzed
then, but here they are organized according
to their reaction types.
A
Acid-Base
O
e. CH3
CH 3
O-H -bond broken
.. NH
H +
3
O
C
CH
Addition
O
O
CH 3
C
CH
CH 3
O
+
-
NH4
+
N-H -bond made
Simple: Total of 2 bonds made and broken. - Acid-Base: H+ transfer
O
O
g.
CH 3
CH 2
C
C
CH 2
C-H -bond broken
+
CH 3
- OCH 3
CH 3
CH 2
C
+
O-H -bond made
-
C
CH
O
CH 3
CH3
CH3
H3O
H2O
b.
C
+
H
O
O
H
C
CH3
O-H -bond broken
CH3
Total of 4 bonds broken and made - Addition: 2 -> 1
C-O -bond broken
O
C-H -bond broken
HOCH 3
Simple: Total of 2 bonds made and broken. - Acid-Base: H+ transfer
+
C
Complex:
O
O
O
a.
C-O -bond broken
C-O & O-H -bonds made
+
H
H
C
N
C-H & C-C -bonds made
H
H2O
O
C
C
N
H
Complex:
Total of 4 bonds broken and made - Addition: 2 -> 1
C-O -bond broken O
d.
CH 3
CH 2
CH 2
O
+
C
H
CH 3
CH 2
CH 2
C
H
C-C -bond made
O
H O H
OH O-H -bond made
C
C
CH 2
H2O
H
CH
CH 3
CH
C-H -bond broken
Complex:
2
CH 3 CH 2
Total of 4 bonds broken and made - Addition: 2 -> 1
Reactions of Carbonyl Compounds-1
c.
C-O - and -bonds broken
2 N-H -bonds broken
O
CH 3
CH 3
Complex:
f.
O
C
Complex:
C
.NH2OH
+
CH 3
Substitutions
C-N - and -bonds made
O
N
H2O
pH ~5
CH 3
C
CH 3
O
H 2 O-H -bonds made
CH 3
+
C-N -bond broken
NH2
+
+
H3O
2 O-H -bonds broken
C
H2O
Total of 8 bonds broken and made - Substitution: 2 -> 2
O
C
2
h. C-H -bond broken
Complex:
C-O -bond made
O
H
+
2 N-H -bonds made
i.
C
CH3
Cl
O
O
C
- OCH 3
H
C
CH 3
O
O-H -bond
made
+ HOCH 3
C-C -bond
made
Total of 4 bonds broken and made - Substitution: 2 -> 2
O
O C-Cl -bond broken
+
NH4
C-O -bond broken
CH 3
O
O
H H
C
CH 3
O
+
C
2 CH3CH2OH
O-H -bond broken
CH3
+
C-O -bond made
-
CH2CH3 + Cl
O +
CH3OH2
O-H -bond made
Total of 4 bonds broken and made - Substitution: 2 -> 2
Complex:
C-O - and
-bonds broken
j.
CH3
CH2
Complex:
2 N-H -bonds broken
NH2
O
HN
C
+
H
CH3
H2O
HN
Total of 4 bonds broken and made - Substitution: 2 -> 2
C
H2O +
NH3
C-N - and -bonds made
CH2
N
N
H
2 O-H -bonds made
H
Total of 8 bonds broken and made - Substitution: 2 -> 2
C. Correlation of the Structures of Carbonyl Compounds with their Reactivity:
Look at the patterns of reactivity for each reaction type of the carbonyl compounds summarized in Section B and try to develop some specific
correlations between the structures of reactants and the outcome of the reactions. Specifically:
All reactions except acid-base reactions seem to involve the carbonyl carbon and/or oxygen.
a. Examine the specific bond changes occurring for each type of reaction. Can either of the complex reaction types (Addition or Substitution) groups
be subdivided? Explain.
In substitution reactions, those that had 4 bonds broken and made had pi and sigma broken and only sigma bonds made. The C=O
(carbonyl) was not separated, but rather something else attached to this C was replaced.
In those that had 8 bonds broken and made, both pi and sigma bonds are broken and made. The C=O was broken and O was substituted
with something else.
3
Reactions of Carbonyl Compounds-1
b. Look more closely at how the reaction outcome (addition or substitution) relates to the overall structure of the carbonyl compound in the reactants.
Is there any correlation between the carbonyl compound structure in the reactants and the overall reaction that takes place? Explain.
c. Is there any correlation of the structure of the other reactant (not considered in b. above) and the overall reaction that takes place? Explain.
Reactions of Carbonyl Compounds-1
4
D. Classification of Reactions According to
:
1. Definition of Reaction Mechanism:
The REACTION MECHANISM is the sequence of reaction steps by which the structures of the reactants are rearranged as the reactants
proceed to the products.
In the following reaction, there are several bonds rearranged and it is not immediately obvious as to how this could occur in one reaction step.
+
Br
2 H2O
+ H3O
O
+
Br
H
Products
Reactants
2. Tools of the Trade: Curved Arrows
As we will see in CHEM 212, the above relatively complex reaction can be dissected into the series of simple reaction steps shown below, which
can be represented by curved arrows as indicated.
a
Br
+
2 H2O
Reactants
b
H2O
c
Br
H2O
Intermediate #1
d
H
H2O
O
H
Br
Intermediate #2
O
H
H3 O
Br
Products
As we discovered in Acid-Base-7, the arrows represent the movement of
. In addition to aiding in drawing new resonance
structures, curved arrows can also help in predicting and understanding the steps in complex reactions. However, in illustrating reaction steps,
arrows depict a bit wider range of electron pair movements.
a. What changes in electron positions are illustrated by arrow a above? How many electrons were moved?
Two electrons in the C-Br bond move to Br making it negative and breaking the bond.
b. What changes in electron positions are illustrated by arrow b above? How many electrons were moved?
Two valence electrons on O of H2O are becoming shared between C and O sharing a bond forming a bond
c. What changes in electron positions are illustrated by arrows c & d above? How many electrons were moved with each arrow?
Two electrons in the OH bond they move to the O making it neutral and breaking the bond. Two electrons on O are being shared between
a separated H forming a bond.
d. How are these electron movements different from those we encountered in using curved arrows to draw resonance structures in Acid-Base-7.
Be as specific as you can.
Bond breakage (from electron movements)results in separation of one molecule into two species rather than bond breakup having no effect
on whether atoms remain connected. Bond formation (from electron movements) makes two species become one
5
Reactions of Carbonyl Compounds-1
2. Applications of Curved Arrows to illustrate reaction steps:
a. Draw curved arrows to account for the movement of electrons in each of the following one-step reactions and classify each reaction as either
substitution, addition or elimination:
1.
H
..
C
N
..
.O.
H
2.
+
CH3
H
..
.I.
H
H3N
CH3
H
+
..
.I.
.O.
..
H
.O.
..
H
H
C
..
.O.
..
..
C
+
..
..
HO
H
3.
..
HO
..
+
C
..
..
NH3
H
N
..
..
H
..
H
H
H
b. Directions of the arrows:
1. For the following reaction, draw the structure of the product formed by the electron movement illustrated by the curved arrow. Be sure to
include all lone pairs of electrons.
..
..
HO
..
H
C
+
.O.
..
H
2. The reactants here are the same as those in 2.a.3. above. How is your product here similar to the product provided in reaction 2.a.3. above?
3. How are the two products different?
4. Based on the energies of the HEE, which product is more likely to form? Explain.
5. What do the above results suggest about the most favorable direction of electron movement in reactions?
Reactions of Carbonyl Compounds-1
6
E. Mechanistic Analysis of Complex Reactions of Carbonyl Compounds (See section B.):
Evaluating Potential Reaction Mechanisms:
For the following reaction, select the mechanism (the sequence of steps) that you believe to be most reasonable. Remember that the most likely
mechanism is generally the one in which the e- energies are kept the lowest throughout the sequence of steps. One high energy intermediate will
make the mechanism less likely. So base your choice on the energies of the e-'s of the intermediates as the reaction proceeds. Explain the logic of your
choice.
Mechanism A
+
: OH +
-
-
+
: OH
: :
-
:O :
: :
O
H
: :
-
: :
H
O+
H
H
: OH
: :
+
:
:O :
: OH
Mechanism B
H
: :
: :
: :
: :
+ -: OH + H O
2
OH
O
H
-
:O :
+
H
-
: :
H
:
:O:
- :O :
: OH
Mechanism C
: OH
:
-
: :
+
O+
H +
-
: :
:O :
H
: OH
: :
H2O
Out of Class Applications:
A. Reading Assignment: CGWW pp. 123-133
B. Problems: CGWW pp. 3 & 5
:O :
+
: :
:
- :O:
: OH
7
Reactions of Carbonyl Compounds-1
Using "Curved Arrows" to describe Organic Reactions
C. For each of the following reactions, write structural formulas for the products that would be formed if the transformation indicated by the "curved
arrows" were to occur. (Be sure to include both the bond sequences and the charges on atoms in the products.) Then classify the overall reaction as
an addition, elimination, substitution or acid-base reaction.
1.
O
N
+
+
O
Cl
2.
CH 3
O
-
CH 3
+
CH 2
+
-
O
CH 3
+ CH 3
CH 2
Cl
H
CH 3
Br
3.
H
CH 3
C
C
4.
O
CH 3
Cl
C
O
Br
H
-
D. Classify each of the following reactions as an addition, elimination, substitution or acid-base reaction. Then, draw the "curved arrows" that would
account for the transformation in one step.
Br
Br
+
1.
..
C
CH3 NH2 C
CH3 NH2
+
O
O 2.
Br
-
+
+
Br
3.
C
CH 2
4.
+
I
+ H
+
C
Cl
.. NH3
+
I
-
+
CH 3 + Cl
. NH3
I
-
+
+
NH4
Classify each step separately and then classify the net effect of both steps together.
Reactions of Carbonyl Compounds-1
8
Investigating Reactions of Carbonyl Compounds
E. Using the structure-reaction correlations discovered in this activity, predict structures for the most likely products of the reactions listed below. No
mechanisms are needed here. Explain the logic that led to your predictions.
O
1.
CH3
2.
CH3
C
O
O
C
O
CH2
CH2
3.
H + H
C
N
O
C
H2 O
CH2
O
- OCH2 CH3
+ CH3
C
CH2
CH3
CH2
CH3
O
+
CH2
H
O
4.
O
C
NH2
- OH
H
H2 O
H2O
+
pH = 6
F. For the following reaction, select the mechanism (the sequence of steps) that you believe to be most reasonable. Remember that the most likely
mechanism is generally the one in which the e- energies are kept the lowest throughout the sequence of steps. One high energy intermediate will
make the mechanism less likely. So base your choice on the energies of the e-'s of the intermediates as the reaction proceeds. Explain the logic of your
choice.
:O :
:O :
:O :
: :
+ : OH
: :
O: +
H2O
: :
O
:O :
-
: :
: :
-
O
H
Mechanism 1:
:O : - :O :
:
:O:
: :
H2O
O: +
H2O
Mechanism 2:
OH
H
:O :
-
O: +
:O :
: :
+ H2O
O
: :
: :
O
Solvent molecule
regenerated
: :
Mechanism 3:
-
+ : OH
: :
Solvent molecule
used
O
:O : - : O :
: :
+ : OH
: :
-
: :
: :
O
H2 O
H
O+ H
:
:O : - : O :
:
:O:
: :
:O :
:O :
: :
O
-
: :
+ : OH
:O :
OH
: :
: :
: :
: :
O
-
: :
:O :
O
H
9
:O:
:O :
H2O
-
O: +
:O :
: :
+ : OH
: :
-
:O :
-
: :
O:
+
: :
+ : OH
H2O
: :
-
: :
: :
O
: :
:O :
Reactions of Carbonyl Compounds-1
: O:
O
H
G. Nomenclature of Aldehydes and Ketones
References:
1. CGWW: Ch. 2 p. 38-9
2. Tutorials:
a. http://chemistry.boisestate.edu/rbanks/organic/nomenclature/organicnomenclature1.htm
Developed by Richard C. Banks, Professor of Chemistry, Boise State University
Provides questions with answers
Sections
Aldehydes
Ketones
b. http://www.molecularmodels.ca/nomenclature/index-2.htm
Developed by Professor Dave Woodcock,
Okanagan University College, British Columbia, Canada
(Contains many examples.)
Sections:
5. Functional Groups with Suffix and Prefix
IV. Alkanones (Ketones)
V. Alkanals (Aldehydes)
Note: Your browser must have the chemscape chime plug-in for these pages to work. Select "1. Introduction to these pages", then click
on "Nomenclature Index - Chemscape Chime" and begin with the "How and Why". If you have problems, go to the
http://www.molecularmodels.ca/nomenclature/nom1.htm and click on "chemscape chime" and follow directions to download the
"chemscape chime plug-in." If you have problems contact me.
3. http://www.acdlabs.com/iupac/nomenclature
Developed by Advanced Chemistry Development Laboratories
(Gives detailed IUPAC rules for nomenclature.)
Recommendations 1993
R-5 Applications to Specific Classes of Compounds
R-5.6 Aldehydes, Ketones, their Derivatives and Analogues
Reactions of Carbonyl Compounds-1
R-5.6.1 Aldehydes, thioaldehydes, and their analogues
R-5.6.2 Ketones, thioketones, and their analogues.
10
4. Applications
11
Reactions of Carbonyl Compounds-1
a. Name the following:
O
O
O
O
O
b. Draw structural formulas for the following compounds:
3-phenyl-2-pentanone
4-bromo-3-ethyl-5-heptenal
3-cyclopentenone
4-methoxybenzaldehyde