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We can build on the concept of sp2 hybridisation
to look at conjugation and aromaticity. Understanding these concepts is essential if you are to fully understand UV vis spectroscopy
What is the relationship between the energy of EM radiation and its wavelength?
Briefly explain the basics of UV-vis spectroscopy. What happens (on a molecular level) when UV light is incident on a suitable molecule?
What is the basic equation underpinning UV-vis spectroscopy?
What are the two most important types of electronic transition for UV-vis spectroscopy? Fully explain your answer.
For the two examples that you have mentioned above provide an example of a structural feature/functional group that would give rise to that type of electronic transition.
Describe the hybridization state of the two atoms marked A and B in the molecules below. Include in your answer appropriate electron configuration diagrams for each atom along with a description of the geometry and bond angles.
Which of the compounds above would you predict to be UV active? Fully explain your answer.
- Yes, because it is an ionic salt and will be very polar.
The key interaction between the molecule and water
will be an ion-dipole interaction
Why would you think that oxybuprocaine hydrochloride would absorb in the UV-visible region of the EM spectrum?
Oxybuprocaine hydrochloride has a max at 308 nm. First you measure a solution of pure oxybuprocaine hydrochloride BP of known concentration (0.8 mM) and found that the absorbance is 0.200 using a quartz cuvette with a pathlength of 1cm. You then measure at the same wavelength a 10-fold dilution of the eye drop formulation containing oxybuprocaine hydrochloride and obtain an absorbance of 0.320 using the same cuvette. What is the concentration of the 10-fold dilution (in M) assuming that there is no interference from the excipients present in the formulation?
What is the concentration (in M) of oxybuprocaine hydrochloride in the eye drop formulation?
The molecular weight of oxybuprocaine hydrochloride is 344.88. Calculate the concentration of oxybuprocaine hydrochloride in the eye drop formulation (in %w/v). Does the formulation comply with the BP specification (0.40% w/v with an allowable range of 95.0 % to 105.0 % of the stated content)?
(3). Draw all of the possible stereoisomers of L-(+)-Threonic acid and
explain the exact stereochemical relationship between each molecule.
(i) Draw the chemical structure of R-2-bromopentane in a
STEREOCHEMICALLY UNAMBIGUOUS fashion.
(ii) Draw the structure of the product of the reaction
and assign its configuration.
(iii) Provide a chemical mechanism for this reaction,
including curly arrows, charges and structures for
all intermediates, and explain what is happening in
each step.
Test Your Knowledge:
(a). Provide a full curly arrow mechanism including all charges and structures for any intermediates for the reaction shown above.
(b). Fully explain why we observe hydrolysis of the ester but no hydrolysis of the amide in this reaction.
(c). Define Hydrolysis
(a). Provide a full curly arrow mechanism including all charges and structures for any intermediates for the reaction shown above.
(b). What is the nucleophilic species in this reaction?
Test Your Knowledge:
(a). Provide a full curly arrow mechanism including all charges and structures for any intermediates for both of the reactions shown above.
(a). Provide a full curly arrow mechanism including all charges and structures for any intermediates for the amide formation reaction shown above.
The acetal is acting as a protecting group for the ketone functional group in compound B. If it were not protected as an acetal then the ketone could get involved in side reactions such as imine formation with the aniline N in compound B or reduction by NaBH4 in step 2 (route 2).
This is an extra video I wanted to share. It's made by my old lecturer from the school of chemistry (Dr Stephenson) and it gives an excellent explanation of the reactivity of enolates
This is a really nice explanation of both a mixed Aldol reaction and an Aldol reaction between two identical molecules. There is a really nice discussion of what base you would choose for each reaction and there is also an explanation of the elimination (condensation) step (this part of the mechanism is missing from my video).
(a). Provide a mechanism including all curly arrows, charges and structures for any intermediates for the reaction of pregnenolone with HBr. Include in your answer an explanation for the REGIOSELECTIVITY that is observed in this reaction.
(b).Provide a mechanism including all curly arrows, charges and structures for any intermediates for the reaction of pregnenolone with Br2. Include in your answer an explanation for the STEREOCHEMICAL outcome of this reaction.
(c).Pregnenolone is capable of exhibiting keto-enol tautomerism. Explain what is meant by keto-enol tautomerism, and draw an alternative tautomeric form of pregnenolone.
This video gives a nice explanation of Molecular Orbitals (in particular antibonding orbitals). It is pitched at a higher level than you need and the content is not examined. So only watch it if you're interested in understanding these concepts at a deeper level.
Test Your Knowledge
Resonance Delocalisation
in Aromatic Rings
Test Your Knowledge (workshop questions and answers:
1. Which of the compounds (A to D) above is conjugated?
UV Active Molecules
2. Which of the compounds (A to D) above is aromatic?
3. Highlight and name all of the functional groups in compound D?
4. Provide curly arrows for the formation of the cation below
5. Fill in the curly arrows for the resonance delocalisation of this charge through the conjugated system
6. Can you spot the error in the model answer I just provided?
7. Fill in the curly arrows the delocalisation of the positive charge around this aromatic system
Test your Knowledge:
What is the hybridisation state of the highlighted atoms in Aspirin? Include in your answer an electron configuration diagram for the atom as well as a description of the Geometry of the bonds, the bond angles.
Shown below is the product of the reaction of Aspirin with NaOH to generate the sodium salt. Highlight the part of the molecule that gives it the ionic salt character.
Test your Knowledge:
Examples of Nucleophiles and
Electrophiles
Intro Chemical Reactions
1. Is the nitrogen in ketorolac basic? Fully explain
your answer.
Test Your Knowledge:
With just one polar functional group (the OH) and a few moderately
polar groups (amine, ether and amide) there is not enough polarity
relative to the hydrocarbon framework to make this drug water soluble.
It could however be converted to a hydrochloride salt via protonation of the
amine to increase it's solubility in water.
For each of the two reactions shown below provide a full curly arrow mechanism (in your answer for each reaction state which species is the electrophile and which is the nucleophile).
2. Which is the most basic nitrogen in procainamide?
Fully explain your answer
Highlight and name all of the functional groups present in the
drug molecules below. Also assess the polarity of each of these
compounds and state whether you think they will be water
soluble:
The carboxylic acid is a very polar functional group (especially when it has
dissociated and is in the anionic form). There is a relatively small hydrocarbon
framework so this is a fairly polar molecule and it will be relatively soluble in water
Hard and Soft Nucleophiles and Electrophiles
Q3. explain how each of these molecules will react
3. Why is the pKa of the highlighted OH group in aspirin
so much lower than the pKa of the highlighted OH
group in compound A?
List all of the peaks you would expect to see
in the IR spectrum for acetyl salicylic acid (include in your answer an estimated wavenumber for each peak)
4. Put these three carboxylic acids in order of DECREASING
pka from left to right
IR Peak Tables
Again, with just one polar functional group (the carboxylic acid) and a few moderately polar groups there is not enough polarity relative to the hydrocarbon framework to make this drug water soluble. However the carboxylic acid can be deprotonated to give the sodium salt form, which should be water soluble.
Test Your Knowledge:
Nucleophilicity vs Basicity
(Wk 7)
Test your Knowledge
In which of these reactions is the ethoxide anion acting as a nucleophile and in which reaction is it acting as a base?
Resonance structures and stabilisation
of negative charge
Test your Knowledge:
(2). Assign the configuration of each of the chiral centres in L-Threonic
acid (below).
(1). If you look at 1,2-dicholorethane from the perspective shown in figure 1,
then there are 6 important conformers to consider (3 staggered and 3
eclipsed). A newman projection for each of these conformers is shown
below. Match each newman projection to the appropriate point on the
energy level diagram (imagine the trio of atoms shown in red are rotating
in a clockwise direction as we have done in the lectures).
This reaction can also be carried out under acidic conditions.
In the final step in the synthesis of paracetamol, diacetylaminophenol is treated with NaOH to give the desired product.
As you can see from the connecting lines these videos are relevant to so many elements of the organic chemistry you see this semester
Test Your Knowledge:
Provide a full curly arrow mechanism including all charges and structures for
any intermediates for both steps in the synthesis of Warfarin shown below.
This step is an aldol condensation
4-hydroxycoumarin exists preferentially in the
enol form due to the greater level of conjugation.
It is easy to deprotonate the OH in this species
to give a nucleophilic enolate anion.
Note how important the concept of tautomerism
is to this reaction.
Shown below is the final two steps in the synthesis of Procainamide.
Shown to the right is the
final two steps in the
synthesis of Procaine
Test Your Knowledge:
Pregnenolone is a steroid hormone involved in the steroidogenesis of progesterone, mineralcorticoids, glucocorticoids, androgens and estrogens.
Clungene is a newly developed pain killer (this is a made up drug).
(1). Shown below are two possible routes for the final stages of the synthesis of clungene (route
and route 2).
(a). If you were a synthetic chemist working in the med chem department of a pharmaceutical
company that was developing clungene, which route would you suggest and why?
Route 2 would be the route of choice even though it is longer. Route 2 corresponds to a reductive amination which can be carried out in a controlled manner unlike route 1. See below for an explanation of the problem with route 1.
(b). Provide a full curly arrow mechanism for steps 1 and in 2 in route 2.
Step 1:
Step 2:
(c). Why is it necessary to have the acetal functional group present in compound B?
(d). Provide a full curly arrow mechanism for step 3 in route 2
Alkylation of Enolates
Aldol Reaction
Resonance Delocalisation
Ionic Bonding and sp3 Hybridisation
Shown below are the structures of aspirin and salicylic acid. Which of these two molecules will be the MOST polar?
Polarity
Periodicity and Orbitals
sp2 and sp Hybridisation