Propose a structure for your product and justify your assignment based on its melting point and its 1H NMR spectrum. The analysis of the 1H NMR spectrum should include a detailed assignment of each of the NMR resonances to the protons found in your structure. NMR analysis should include reasoning used to exclude other aldehydes and ketones from your structural assignment. For example, no signals were observed between 0-4 ppm indicating no H atoms bound to sp3 hybridized carbons. It can be concluded from this observation that no ketone or aldehyde that would retain a H bound to sp3 hybridized carbons were used as starting materials.
Propose a structure for your product and justify your assignment based on its melting point and its 1H NMR spectrum. The analysis of the 1H NMR spectrum should include a detailed assignment of each of the NMR resonances to the protons found in your structure. NMR analysis should include reasoning used to exclude other aldehydes and ketones from your structural assignment. For example, no signals were observed between 0-4 ppm indicating no H atoms bound to sp3 hybridized carbons. It can be concluded from this observation that no ketone or aldehyde that would retain a H bound to sp3 hybridized carbons were used as starting materials.
Propose a structure for your product and justify your assignment based on its melting point and its 1H NMR spectrum. The analysis of the 1H NMR spectrum should include a detailed assignment of each of the NMR resonances to the protons found in your structure. NMR analysis should include reasoning used to exclude other aldehydes and ketones from your structural assignment. For example, no signals were observed between 0-4 ppm indicating no H atoms bound to sp3 hybridized carbons. It can be concluded from this observation that no ketone or aldehyde that would retain a H bound to sp3 hybridized carbons were used as starting materials.
Propose a structure for your product and justify your assignment based on its melting point and its 1H NMR spectrum. The analysis of the 1H NMR spectrum should include a detailed assignment of each of the NMR resonances to the protons found in your structure. NMR analysis should include reasoning used to exclude other aldehydes and ketones from your structural assignment. For example, no signals were observed between 0-4 ppm indicating no H atoms bound to sp3 hybridized carbons. It can be concluded from this observation that no ketone or aldehyde that would retain a H bound to sp3 hybridized carbons were used as starting materials.
Transcribed Image Text:You will be assigned a ketone and an aldehyde from the following list of starting reagents
for your aldol condensation.
EXPERIMENT 3
ALDOL-DEHYDRATION REACTION USING
UNKNOWN ALDEHYDES AND KETONES
BACKGROUND:
cyclopentanone
cyclohexanone
4-methylcyclohexanone
cyclaheptanone
acetone
The formation of carbon-carbon bonds is of fundamental importance in synthetic organic
chemistry, and the aldol condensation has a long and successful history as a method of carbon-
carbon bond formation. The base-promoted condensation of a molecule of benzaldehyde (1) with
a molecule of acetophenone (2) represents a typical aldol condensation between two different
carbonyl compounds. In a base-catalyzed reaction, the aldol product 3 can subsequently lose a
molecule of water (dehydrate) to form an a.B-unsaturated carbonyl (4).
сно
CHO
Meo
4-methylberzaldehyde
p-tolualdehyde)
4-methoxybenzaldehyde
panisaldehyde
E-3-phenypropenal 2-furaldehyde
(cimamaldehyde)
benzaldehyde
(furfural)
NaOH, BOH
1.
Whereas the ketone, acetophenone, has a-protons and can react with hydroxide to form an
enolate anion, benzaldehyde cannot do so because it has no a-protons. The elimination of water
from the aldol product occurs in two steps. The first step is the formation of an enolate anion by
base-catalyzed abstraction of an a-proton from the aldol condensation product, The second is the
expulsion of the hydroxide anien to form the conjugated dehydration product.
In this experiment you will carry out an aldol condensation between an unknown
aldehyde and an unknown ketone (structures below). Your task is to identify the aldehyde and
ketone starting materials.
Symmetrical ketones will be used for all aldol condensation reactions in this experiment.
Under the reaction conditions, two dehydration reactions occur to produce symmetrical products.
Two molecules of an aromatic aldehyde will condense with one molecule of a symmetrical ketone
to form, after dehydration, an extensively con ju gated product. Using an excess of the aldehyde
ensures that a double aldol-dehydration cycle occurs in the reaction. The double aldol-dehydration
reaction that would occur with acetone and benzaldehyde is below.
Table of melting points for the aldol-dehydration products formed from the reaction of the
above ketones and aldehydes.
Ketone
Aldehyde
cvclopentanone
cvdohexanone
4-Me-cvelohexanone evloheptanone
acetone
113 C
I89-190 C
118-1 19 "C
98-99 "C
106-107"C
benzaldehyde
170 °C
134-136 "C
131-133°C
tolualdehyde
175 C
23235 C
NaOH. EIOH
136 "C
128-129 C
anisaldehyde
129-130 "C
212-214°C
160-162 C
+ 2
cinnamaldehyde
144-145 C
223-225 "C
INO-18I C
163-164 C
198-199°C
To characterize your unknown compounds, you need to obtain a melting point of the
166-168 C
96-97 C
114'C
145-146°C
2-furaldchyde
aldol-dehydrat ion product and an 'H NMR spectrum of the product. Anal ysis of the 'H NMR
spectrum will allow you to draw conclusions about the structure of your aldol-dehydration product
and, by deduction, the structures of the aldehyde and ketone you used as starting materials for the
reaction.
Definition Definition Organic compounds that have a carbonyl group, C=O, as their functional group. The carbonyl group in aldehydes is placed at the end of the molecular structure, which means the C=O is attached to one hydrogen atom and an alkyl group or a benzene ring. Just like all the other homologous series in organic chemistry, the naming of aldehydes uses the suffix “-al”. The general molecular formula is C n H 2n O.
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