Official DAT Destroyer Q&A Thread

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densaugeo

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Hi guys, since I'm currently going through the DAT Destroyer and I'm sure many of you guys are as well I felt this thread would be helpful. I usually have various questions while going through Destroyer regarding why a certain answer choice is correct or other times I am in need of a more detailed explanation.

Instead of making multiple threads each time we have questions, I thought we could just post them here and anyone can chime in with an explanation or further clarification.

Please don't post entire questions as that would be a violation of copyright. You can ask specific questions regarding a particular problem in the Destroyers.

Hopefully others find this a useful thread. Thanks!

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I'll start off with a question I had regarding the Bio section, question 54 (2015 Destroyer), it asks what isn't true about a vaccine and the answer was that attenuated vaccines contain a low concentration of the pathogen and will illicit an immune response.

I couldn't really figure out why this was the correct answer. I read that in attenuated vaccines, live virus particles with low virulence are administered, and that the advantages are that all parts of the immune system are activated (according to wikipedia) so I was wondering why this was the correct answer?

Thanks for your help!
 
I'll start off with a question I had regarding the Bio section, question 54 (2015 Destroyer), it asks what isn't true about a vaccine and the answer was that attenuated vaccines contain a low concentration of the pathogen and will illicit an immune response.

I couldn't really figure out why this was the correct answer. I read that in attenuated vaccines, live virus particles with low virulence are administered, and that the advantages are that all parts of the immune system are activated (according to wikipedia) so I was wondering why this was the correct answer?

Thanks for your help!

Here is a well written essay ...I hope this live, attenuated vaccines contain a version of the living microbe that has been weakened in the lab so it can’t cause disease. Because a live, attenuated vaccine is the closest thing to a natural infection, these vaccines are good “teachers” of the immune system: They elicit strong cellular and antibody responses and often confer lifelong immunity with only one or two doses. Despite the advantages of live, attenuated vaccines, there are some downsides. It is the nature of living things to change, or mutate, and the organisms used in live, attenuated vaccines are no different. The remote possibility exists that an attenuated microbe in the vaccine could revert to a virulent form and cause disease. Also, not everyone can safely receive live, attenuated vaccines. For their own protection, people who have damaged or weakened immune systems—because they’ve undergone chemotherapy or have HIV, for example—cannot be given live vaccines. Another limitation is that live, attenuated vaccines usually need to be refrigerated to stay potent. If the vaccine needs to be shipped overseas and stored by healthcare workers in developing countries that lack widespread refrigeration, a live vaccine may not be the best choice. Live, attenuated vaccines are relatively easy to create for certain viruses. Vaccines against measles, mumps, and chickenpox, for example, are made by this method. Viruses are simple microbes containing a small number of genes, and scientists can therefore more readily control their characteristics. Viruses often are attenuated through a method of growing generations of them in cells in which they do not reproduce very well. This hostile environment takes the fight out of viruses: As they evolve to adapt to the new environment, they become weaker with respect to their natural host, human beings. Live, attenuated vaccines are more difficult to create for bacteria. Bacteria have thousands of genes and thus are much harder to control. Scientists working on a live vaccine for a bacterium, however, might be able to use recombinant DNA technology to remove several key genes. This approach has been used to create a vaccine against the bacterium that causes cholera, Vibrio cholerae, although the live cholera vaccine has not been licensed in the United States. Inactivated Vaccines Scientists produce inactivated vaccines by killing the disease-causing microbe with chemicals, heat, or radiation. Such vaccines are more stable and safer than live vaccines: The dead microbes can’t mutate back to their disease-causing state. Inactivated vaccines usually don’t require refrigeration, and they can be easily stored and transported in a freeze-dried form, which makes them accessible to people in developing countries. Most inactivated vaccines, however, stimulate a weaker immune system response than do live vaccines. So it would likely take several additional doses, or booster shots, to maintain a person’s immunity. This could be a drawback in areas where people don’t have regular access to health care and can’t get booster shots on time.

Hope this helps.
 
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Thank you that was helpful. So is the answer "attenuated vaccines contain a low concentration of the pathogen and will illicit an immune response" false because attenuated vaccines contain a high concentration of inactivated pathogen?
 
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Good idea making this thread!

I had a question on one of the gen chem problems.

Gen Chem Q 243

At zero C gas is dissolved in H2O at a mole fraction of 2 x 10 -18. What is the molality of this solution give the molecular weight of the gas is 32 g/mol?

1. Why is the mole fraction of 2 x 10 -18 the amount of moles in the solution? Since the mole fraction is moles of gas/ moles gas + moles h20 shouldn't the amount of moles of gas be different?

2. Why do you assume 1 mole of solvent?
 
Good idea making this thread!

I had a question on one of the gen chem problems.

Gen Chem Q 243

At zero C gas is dissolved in H2O at a mole fraction of 2 x 10 -18. What is the molality of this solution give the molecular weight of the gas is 32 g/mol?

1. Why is the mole fraction of 2 x 10 -18 the amount of moles in the solution? Since the mole fraction is moles of gas/ moles gas + moles h20 shouldn't the amount of moles of gas be different?

2. Why do you assume 1 mole of solvent?

The gas represents the solute since it is being dissolved........since molality is based on kg of SOLVENT.....indeed the amount of water is not given.....in a case like this,,,,,a commonly asked trick problem......base it on 1 mole. That being said, we have 18g or .018kg of the solvent.

Hope this helps

Dr. Romano
 
Great thread!


I think there is a mistake in the explanation of Question 59 of the Bio section.

It states that freshwater fish live in a hypoosmotic environment. (Don't they live in a hypotonic/hyperosmotic environment?)

Also, it states that marine fish live in a hyperosmotic environment, shouldn't it be hypoosmotic environment/hypertonic environment (the environment has a lower concentration of water & higher concentration of salts compared to the fish).
 
Freshwater fish are hypertonic to their water environment and therefore, water is continually diffusing into the fish through the gill membranes into the blood. while water moves in towards the higher osmotic pressure of the blood, sodium and chloride ions also diffuse out of the fish, moving down their concentration gradients to the external environment. Marine fish experience the opposite situation as their bodies are hypotonic to their saltwater environment. The continual uptake of water in freshwater species is regulated by the kidneys which continually produce large amounts of dilute urine.

Hope this helps...Nancy
 
I wish this thread existed when I was studying haha good luck everyone!
 
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Hey @orgoman22 I am going through your roadmaps....do you have any recommendations on how to memorize all of these?

Hi Hopefuldent,

Try writing them out.......and filling in the blanks. Most students try to understand the pattern of what to do with each functional group...For example.....alkenes and alkynes do addition reactions.....

Hope this helps.

Dr. Jim Romano
 
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Biology Question 102
what does 'n' stands for and how are n, n+1, and n-1 related to chromosomal pair?
Hi Jack,

n is the number of chromosomes in a haploid cell.....n+1 means an extra chromosome....n-1 means one chromosome is missing.

Hope this helps!

Dr. Romano
 
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I just had a quick question from the orgo section of the destroyer.

Q6O

I guessed that both SOCl2 and HCL could cause the reaction.

I knew that SOCl2 definitely caused the reaction but I was unsure about HCl.

I guessed HCl because I thought that the OH group on the alcohol would grab the H from HCl creating Cl-. I thought that since Cl- is a fairly good nucleophile it would cause the reaction to undergo SN1 to produce the product?

It looks like from the answers that it undergoes SN1 with a rearrangement.

Is Cl- considered a weak nucleophile which causes SN1?
 
I just had a quick question from the orgo section of the destroyer.

Q6O

I guessed that both SOCl2 and HCL could cause the reaction.

I knew that SOCl2 definitely caused the reaction but I was unsure about HCl.

I guessed HCl because I thought that the OH group on the alcohol would grab the H from HCl creating Cl-. I thought that since Cl- is a fairly good nucleophile it would cause the reaction to undergo SN1 to produce the product?

It looks like from the answers that it undergoes SN1 with a rearrangement.

Is Cl- considered a weak nucleophile which causes SN1?

You have missed a critical point. As explained in the solution......If HCl was used, the reaction would yield the rearranged product. SOCl2 prevents the rearrangement and maintains the structural integrity by doing an SN2 like reaction...... in other words,,,,,OH is replaced with no rearrangements ! If you used HCL......what would occur ? You protonate the alcohol..... as it leaves, a shift occurs to generate the tertiary carbocation giving the 2-chloro-2 methylpropane isomer as the major product !!

Hope this helps

Keep up the good work!

Dr. Jim Romano
 
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Hi Jack,

n is the number of chromosomes in a haploid cell.....n+1 means an extra chromosome....n-1 means one chromosome is missing.

Hope this helps!

Dr. Romano

I still don't understand how n-1, n-1, n+1, n+1 can be a failed meiosis I of anaphase and failed anaphase II is n+1, n-1, n, n.
 
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@orgoman22 In the orgo section of #55 could you please explain how a 1-chloro-2-methyl-butane can be chiral and have an enantiomer? Thank you.

For problem #55.......When chlorine is put on the first position......it generates a chiral center at C2 !!!!! This was tricky, because usually the chiral center was generated at that carbon that was substituted by chlorine !!

Hope this helps...
Dr. Jim Romano
 
I was just curious if the trig formulas in the math destroyer were all we should really know. I spent the last couple days going through almost all of the videos on khan academy to make sure I was refreshed, since this is an area I felt the worst about.
 
For problem #55.......When chlorine is put on the first position......it generates a chiral center at C2 !!!!! This was tricky, because usually the chiral center was generated at that carbon that was substituted by chlorine !!

Hope this helps...
Dr. Jim Romano

Thanks for the reply, dang that's a good question
 
I was just curious if the trig formulas in the math destroyer were all we should really know. I spent the last couple days going through almost all of the videos on khan academy to make sure I was refreshed, since this is an area I felt the worst about.

Yes the Math destroyer covers everything you need to know about trig. Also make sure you know sine, cosine and tangent of basic angles ( 30, 45, 60, 90 etc...)

Good luck on the DAT

Nancy
 
Hello can anyone explain what is in the organic odyssey book? I would like to buy it but i dont know what it contains
 
Destroyer '14 version

Q #151: which compound nitrates most rapidly?


Not entirely sure what the verb "nitrates" really means.

Does that mean a compound reacts with a nitrates and forms a Nitro group? NO3- + R ----> R-NO2
or
Does it mean a compound obtains a nitrate group? NO3- + R -----> R-ONO2

I'm guessing its when a nitro group is formed because the answer is anisole.. which would make the benzene ring more e- rich which would allow for electrophilic subsitution occur with the nitrogen in nitrate?
 
Just curious if Orgo question #33 is simply a 6 ring product because of 5 or 6 rings being preferred or if it has more to do with the proton being removed is more acidic somehow (versus the alpha protons on the other end of the ketone)?
 
Just curious if Orgo question #33 is simply a 6 ring product because of 5 or 6 rings being preferred or if it has more to do with the proton being removed is more acidic somehow (versus the alpha protons on the other end of the ketone)?

Cannot tell what your question is without knowing the DAT Destroyer version you are using, which may not be the same as most others.
 
On DAT Destroyer 2014, Organic Chemistry, problem #39: I cannot figure out why choice B) has 4 distinct carbons (and is the correct answer) but choice E) has five (thus the wrong answer). I'm supposing this has something to do with the slight "symmetry" of the iso-like part of choice B, but I'm not 100% sure. This doesn't seem to be a question that has been asked before, so hopefully it's just something small I'm missing.

I've attached a picture of the problem. I hope that's alright!

Choice B does indeed have 4 distinct carbons. Starting from the left.......we see a distinct methyl carbon.....then a carbonyl......then another carbon adjacent......THEN.....two methyls at the far right that are EQUIVALENT due to symmetry.

This is quite important....practice being able to recognize symmetry elements !

Hope this helps

Dr. Jim Romano
 
Destroyer '14 version

Q #151: which compound nitrates most rapidly?


Not entirely sure what the verb "nitrates" really means.

Does that mean a compound reacts with a nitrates and forms a Nitro group? NO3- + R ----> R-NO2
or
Does it mean a compound obtains a nitrate group? NO3- + R -----> R-ONO2

I'm guessing its when a nitro group is formed because the answer is anisole.. which would make the benzene ring more e- rich which would allow for electrophilic subsitution occur with the nitrogen in nitrate?

OK.....Nitrates most rapidly means addition of the NO2 group.....thus we are simply looking for the starting compound that is most activating. One can halogenate, alkylate, or sulfonate,,,,,,,the terms simply means to add these groups on.

Hope this helps

Dr. Jim Romano
 
Choice B does indeed have 4 distinct carbons. Starting from the left.......we see a distinct methyl carbon.....then a carbonyl......then another carbon adjacent......THEN.....two methyls at the far right that are EQUIVALENT due to symmetry.

This is quite important....practice being able to recognize symmetry elements !

Hope this helps

Dr. Jim Romano

Thank you for your response! It's nice to know I was at least on the right path and my issue may have been mainly confidence in my answer. I'm freshly learning spectroscopy since I really didn't cover it in university.

(Also, saw you had to delete my post because of the picture - my apologies, but thank you so much for answering! I greatly appreciate it!)
 
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Thank you for your response! It's nice to know I was at least on the right path and my issue may have been mainly confidence in my answer. I'm freshly learning spectroscopy since I really didn't cover it in university.

(Also, saw you had to delete
my post because of the picture - my apologies, but thank you so much for answering! I greatly appreciate it!)

Always glad to help and an honor to a part of the SDN community. If you have more questions feel free to ask.

Dr. Jim Romano
 
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#C27: PH of 1x10^-12M HCl?

Can someone explain why the answer is pH=7?

Normally, we don't consider the fact that when we put something in a solution of water, the solution itself already has H+ in it...at a concentration of 1x10^-7 (because as you already know, the pH of water is 7). Since we usually add acid of concentrations much higher than is already in solution from water, we generally ignore the contribution of H+ from water that is already there (if you had 3 pennies and I handed you a million dollars, you would reasonably just say 'I have a million dollars now' instead of 'I have a million dollars and 3 cents' because the 3 cents is insignificant compared to the larger sum). Adding H+ at a concentration of 1x10^-12 is adding an extremely dilute quantity of acid to an already significantly higher concentration of it that's already in the water. So the pH is effectively just 7, because you added barely anything to what's already in water.

If you want more detail: http://www.chemteam.info/AcidBase/Trick-pH-question.html
 
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#C27: PH of 1x10^-12M HCl?

Can someone explain why the answer is pH=7?


You are given an acid that has an EXTREMELY low concentration.......thus one must consider the hydrolysis of water ! Water will contribute 1x10 exp-7.......thus pH will be close to 7. Lets say that you forget to do this.....the negative log of 1x10exp-12 would have given you a pH of 12....yes ? How can an HCl solution be 12 ? That would be the tell-tale sign that this is a trick problem !

Hope this helps.

Dr. Jim Romano
 
GC Question # 47 (Destroyer 2015). I am confused as to why the hybridization of the sulfur atom is sp3 as opposed to sp2? Wouldn't the double bond give the sulfur an sp2 hybridization?

Thanks in advance. Except for this question, DAT Destroyer questions are great! Proves to be a great resource.
 
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GC Question # 47 (Destroyer 2015). I am confused as to why the hybridization of the sulfur atom is sp3 as opposed to sp2? Wouldn't the double bond give the sulfur an sp2 hybridization?

Thanks in advance. Except for this question, DAT Destroyer questions are great! Proves to be a great resource.

Look at the geometry of the molecule.....We have 3 bonded areas plus a LONE electron pair......this give " 4 regions " of electron density......hence sp3 hybridization......another way to look at it is by its shape.....the shape is trigonal pyramidal.......and being such necessitates sp3 hybridization.

Hope this helps

Dr. Jim Romano
 
I am having trouble. How do you know a reaction is going to be a Dieckmann, how do you spot it really fast?
 
I have done this reaction successfully for many years. The Hallmark structural feature is that of a Diester with a span of 4 or 5 carbons.....being treated with a base such as sodium ethoxide or sodium methoxide. If the diester has a span of 4 carbons, a 5 membered ring will result. If the span is 5 carbons, a 6 membered ring results. This reaction is one of the nicest ways to install ring systems . If the diester has ethyl groups, use ethoxide as the base,,,,,if methyl groups are present, use methoxide as the base.

Hope this helps.

Dr. Romano
 
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Thanks for answering my previous question, I was getting SO2 and SO2(2-) hybridizations confused.

Not sure if this is a typo or not? Destroyer 2015 GC #66. All the answers are correct and the answer should be E. In the answer key it says D. Maybe my brain is tired, been through a lot of DD questions today and I'm just seeing things.
 
Thanks for answering my previous question, I was getting SO2 and SO2(2-) hybridizations confused.

Not sure if this is a typo or not? Destroyer 2015 GC #66. All the answers are correct and the answer should be E. In the answer key it says D. Maybe my brain is tired, been through a lot of DD questions today and I'm just seeing things.

That was a typo and has already been corrected.

Keep up the good work!
 
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GC #153 I am completely lost in this question...

how do you know deltaE1 is equal to 800 kJ/mole?
how do you solve for delta E1 ~ E5?
what do 1st, 2nd, 3rd, 4th, and 5th stand for?

perhaps I am not getting the bigger picture in this question...?
 
GC #153 I am completely lost in this question...

how do you know deltaE1 is equal to 800 kJ/mole?
how do you solve for delta E1 ~ E5?
what do 1st, 2nd, 3rd, 4th, and 5th stand for?

perhaps I am not getting the bigger picture in this question...?
Indeed,,,,,,you have missed the point. These were only literature values to illustrate the concept. Silicon has 4 valence electrons.....thus can be removed reasonably easy,,,,the 5th electron is part of a stable Noble gas core and would be very LARGE. I used these values just to illustrate this point.

Hope this helps

Dr. Jim Romano
 
Hi,

Destroyer '14 version Gen Chem Q.93.
Why is the Br in KBr is a spectator ion and is crossed out, while F in NaF isn't? Is there a fast way to determine what gets crossed out and what not?

Thanks
 
Hi,

Destroyer '14 version Gen Chem Q.93.
Why is the Br in KBr is a spectator ion and is crossed out, while F in NaF isn't? Is there a fast way to determine what gets crossed out and what not?

Thanks
Br is a spectator because it is the anion of a strong acid......All anions of strong acids are spectators.....NO3-, I-, Cl-, Br- are great example. F- is NOT a spectator since this anion isn't derived from a strong acid. Now lets recap.... Spectators are Anions of STRONG acids,,,,,or cations of Strong Bases......thus Na+, K+, Li+...would all be spectators.

Hope this great trick helps.

Dr. Romano
 
OC # 245 I was going through and why would a complex of 2,2- dimethylpentane have a higher melting point over stacking of the pentane. Also I was looking at my O-chem textbook and saw this
o-chem 2.17.jpg
 
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