CHEM 2364 Final Exam and All Actual
Answers.
The Dehydration Reaction - Answer When the 'OH' group of an alcohol is removed, along
with the proton on an adjacent carbon, this reaction is referred to as dehydration, because
water is a product and is removed from the molecule.
In experiment 7 you used... - Answer a simple distillation set-up for the dehydration reaction
of 2-methylcyclohexanol to produce an assortment of cyclohexene isomers.
The first product (1-methyl-1-cyclohexene) should be the major product because... - Answer
the major product is determined by the stability of the carbocation intermediate. A tertiary
carbocation is more stable than a secondary carbocation; and a secondary is more stable than a
primary carbocation. Thus, it is expected that a secondary carbocation will move, through a
hydride shift, to become a tertiary carbocation.
Distillation description - Answer One of the more common methods by which a mixture of
two liquids (or a binary mixture) can be separated in organic chemistry is using the process of
distillation. This is based upon the theory that since two different liquids have two different
boiling points, the one with the lower bp (molecule "A") will evaporate into the gas phase
before the other (molecule "B"). When it evaporates into the gas phase, it can be condensed
into a purified liquid called the distillate in a separate container.
Simple distillation technique - Answer A simple distillation is sufficient to separate the
different products from the reactants since the bp are different enough. This distillation will
collect the products in a RBF (not in fractions), because the bps of the products are too similar.
Water is a byproduct; it will distill along with the other products since it has a similar bp. Water
forms a positive azeotrope with the hydrocarbon products, and the effect is a bp around 80
degrees celsius.
Simple distillation technique cont. - Answer A positive azeotrope is one where the bp of the
azeotrope is lower than that of the individual components, and a negative azeotrope has a
higher boiling point than its components. Since water is generally immiscle with non-polar
hydrocarbons (such as these products), once distilled over, water will form a second layer, which
will be on the bottom due to its greater density than that of the dehydration products.
Experiment 8 EAS Reactions - Answer While benzene is a stable molecule due to its
aromaticity, certain reagents can be used to add various substituents onto the ring. One such
substituent is a nitro (NO2) group, and the reaction used to add this functional group is called a
nitration.
, EDG vs. EWG - Answer Electron Donating Groups (EDG) as well as halogens, are said to be
ortho, para (o,p) directers because the second substituent will add to the ortho or the para
position. Other functional groups are Electron Withdrawing Groups (EWG), which results in the
second substituent adding to the meta position, so these are meta (m) directors.
ortho --> (1,2)
para --> (1,4)
meta --> (1,3)
Experiment 8 product - Answer Bromine, being a halogen, is an o,p director, and so the
reaction conducted in this experiment results in a nitro group being added to the para position.
The ortho position is sterically hindered (esentially blocked) due to the somewhat large Br atom
and bulky nitro group. So the para position is the major product.
Nuclear Magnetic Resonance (NMR) Spectroscopy - Answer In organic chemistry, NMR
spectroscopy is a technique used to verify the structure of a molecule. This technique focuses
on a signal generated from each H atom (most common, although C can also be studied).
Because each H gives a signal (which is a peak), this technique can generally tell the number of
H atoms in a molecule by integrating the area beneath the peak. Furthermore, the type of signal
that each H atom gives is unique, dependent upon its location in relation to various functional
groups as well as in relation to adjacent H atoms.
The position of a H atom (often referred to as a proton) to various functional groups can be
determined by its chemical shift, which is the location of the peak along the x-axis of the
spectrum. The range references specifically the H atoms in bold.
NMR cont. - Answer Additionally, if there are any protons on the atom adjacent to that H
atom, the peak will split. A doublet (when the peak splits into 2) means that there is 1 adjacent
H atom (i.e., a H atom on the neighboring atom, typically C). If there are 2 adjacent protons,
then the peak splits into 2+1, or 3 peaks (triplet). If there are 3 adjacent protons, then the peak
splits into 3+1, or 4, peaks (quartet). The H in bold is the one that "sees" the adjacent protons
and its peak splits.
Experiment 9 background: Stereochemistry Concepts and Terms - Answer If a carbon is
connected to 4 different atoms or functional groups, this carbon is said to be chiral. This chiral
carbon is a stereocenter in a molecule (a location where the stereochemistry is unique).
Typically, the way that this is visualized is to label the different groups in order of priority, then
the molecule is rotated such that the lowest priority group is placed in the background. The
sequence of three remaining groups in the foreground is then counted, either in a clockwise or
counterclockwise direction. The clockwise direction is labeled as the R enantiomer, and the
counterclockwise direction is labeled as the S enantiomer. An enantiomer is a special type of
stereoisomer that differs in the orientation of the chiral carbon, such that enantiomers are non-
superimposable, and they are mirror images of one another. Each stereoisomer has different
physical properties.
Answers.
The Dehydration Reaction - Answer When the 'OH' group of an alcohol is removed, along
with the proton on an adjacent carbon, this reaction is referred to as dehydration, because
water is a product and is removed from the molecule.
In experiment 7 you used... - Answer a simple distillation set-up for the dehydration reaction
of 2-methylcyclohexanol to produce an assortment of cyclohexene isomers.
The first product (1-methyl-1-cyclohexene) should be the major product because... - Answer
the major product is determined by the stability of the carbocation intermediate. A tertiary
carbocation is more stable than a secondary carbocation; and a secondary is more stable than a
primary carbocation. Thus, it is expected that a secondary carbocation will move, through a
hydride shift, to become a tertiary carbocation.
Distillation description - Answer One of the more common methods by which a mixture of
two liquids (or a binary mixture) can be separated in organic chemistry is using the process of
distillation. This is based upon the theory that since two different liquids have two different
boiling points, the one with the lower bp (molecule "A") will evaporate into the gas phase
before the other (molecule "B"). When it evaporates into the gas phase, it can be condensed
into a purified liquid called the distillate in a separate container.
Simple distillation technique - Answer A simple distillation is sufficient to separate the
different products from the reactants since the bp are different enough. This distillation will
collect the products in a RBF (not in fractions), because the bps of the products are too similar.
Water is a byproduct; it will distill along with the other products since it has a similar bp. Water
forms a positive azeotrope with the hydrocarbon products, and the effect is a bp around 80
degrees celsius.
Simple distillation technique cont. - Answer A positive azeotrope is one where the bp of the
azeotrope is lower than that of the individual components, and a negative azeotrope has a
higher boiling point than its components. Since water is generally immiscle with non-polar
hydrocarbons (such as these products), once distilled over, water will form a second layer, which
will be on the bottom due to its greater density than that of the dehydration products.
Experiment 8 EAS Reactions - Answer While benzene is a stable molecule due to its
aromaticity, certain reagents can be used to add various substituents onto the ring. One such
substituent is a nitro (NO2) group, and the reaction used to add this functional group is called a
nitration.
, EDG vs. EWG - Answer Electron Donating Groups (EDG) as well as halogens, are said to be
ortho, para (o,p) directers because the second substituent will add to the ortho or the para
position. Other functional groups are Electron Withdrawing Groups (EWG), which results in the
second substituent adding to the meta position, so these are meta (m) directors.
ortho --> (1,2)
para --> (1,4)
meta --> (1,3)
Experiment 8 product - Answer Bromine, being a halogen, is an o,p director, and so the
reaction conducted in this experiment results in a nitro group being added to the para position.
The ortho position is sterically hindered (esentially blocked) due to the somewhat large Br atom
and bulky nitro group. So the para position is the major product.
Nuclear Magnetic Resonance (NMR) Spectroscopy - Answer In organic chemistry, NMR
spectroscopy is a technique used to verify the structure of a molecule. This technique focuses
on a signal generated from each H atom (most common, although C can also be studied).
Because each H gives a signal (which is a peak), this technique can generally tell the number of
H atoms in a molecule by integrating the area beneath the peak. Furthermore, the type of signal
that each H atom gives is unique, dependent upon its location in relation to various functional
groups as well as in relation to adjacent H atoms.
The position of a H atom (often referred to as a proton) to various functional groups can be
determined by its chemical shift, which is the location of the peak along the x-axis of the
spectrum. The range references specifically the H atoms in bold.
NMR cont. - Answer Additionally, if there are any protons on the atom adjacent to that H
atom, the peak will split. A doublet (when the peak splits into 2) means that there is 1 adjacent
H atom (i.e., a H atom on the neighboring atom, typically C). If there are 2 adjacent protons,
then the peak splits into 2+1, or 3 peaks (triplet). If there are 3 adjacent protons, then the peak
splits into 3+1, or 4, peaks (quartet). The H in bold is the one that "sees" the adjacent protons
and its peak splits.
Experiment 9 background: Stereochemistry Concepts and Terms - Answer If a carbon is
connected to 4 different atoms or functional groups, this carbon is said to be chiral. This chiral
carbon is a stereocenter in a molecule (a location where the stereochemistry is unique).
Typically, the way that this is visualized is to label the different groups in order of priority, then
the molecule is rotated such that the lowest priority group is placed in the background. The
sequence of three remaining groups in the foreground is then counted, either in a clockwise or
counterclockwise direction. The clockwise direction is labeled as the R enantiomer, and the
counterclockwise direction is labeled as the S enantiomer. An enantiomer is a special type of
stereoisomer that differs in the orientation of the chiral carbon, such that enantiomers are non-
superimposable, and they are mirror images of one another. Each stereoisomer has different
physical properties.
