Official DAT Destroyer Q&A Thread

[densaugeo]

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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[DMikes]

Destroyer 2016 Gen Chem Q 143. The answer is "e) A and C" and I just wanted to clarify that it is e because of the terminology used in answer c. If it had said "Magnesium has a third ionization energy significantly higher than its second ionization energy" rather than slightly the answer would've been a, correct?

 

[DAT Destroyer]

Destroyer 2016 Gen Chem Q 143. The answer is "e) A and C" and I just wanted to clarify that it is e because of the terminology used in answer c. If it had said "Magnesium has a third ionization energy significantly higher than its second ionization energy" rather than slightly the answer would've been a, correct?

You are correct.....Mg is in Group 2,, thus we can remove 2 electrons rather easily to form the divalent Mg+2 cation. If a third electron was to be removed.....the energy would be VERY HIGH......since we are removing that electron from a stable core.

Hope this helps

Dr. Romano

 

[DAT Destroyer]

I found conflicting information regarding the normality of H2SO4. Chad says that if you have, say, 1 M of H2SO4 then you'll actually end up having a molarity (or normality) of slightly higher than 1 M because only the first H dissociates completely because H2SO4 is a strong acid. The second H will only partially dissociate because we are now starting with HSO4- which is no longer a strong acid, but rather a weak acid. This makes sense. But, I found a question in Destroyer that says that the normality of H2SO4 will actually be twice the molarity, not just slightly higher- implying that both of the H's dissociate completely, which doesn't make sense to me. I thought the only time when both of the H's/OH's dissociated completely was when we had a strong base with 2 OH's on it, like Ca(OH)2. Anyone?

No.....In analytical chemistry we sometimes must be careful since the pKa 2 is greater than pKa 1. Not for the DAT,,,,,,,,ASSUME BOTH hydrogens fully dissociate. You will not be given any constants,,,,,,,,,Thus a 1M solution is 2N. If you do a Google search on this, a few PhD chemists use this as a nice approximation .

Hope this helps.

Dr. Romano

 

[DentalNucleicAcid]

No.....In analytical chemistry we sometimes must be careful since the pKa 2 is greater than pKa 1. Not for the DAT,,,,,,,,ASSUME BOTH hydrogens fully dissociate. You will not be given any constants,,,,,,,,,Thus a 1M solution is 2N. If you do a Google search on this, a few PhD chemists use this as a nice approximation .

Hope this helps.

Dr. Romano

Oh ok, got it. Thank you!

 

[FutureDDS_11]

Hello,
I am slightly confused for OG #133.
So the answer is that all of them produce that certain product. My question is when adding Acetic acid, H3O+, why is it that we still get the acetic acid attacking the cyclohexanol and not having dehydration occur and forming a cation? Wouldn't the acetic acid have to be converted to a carbonyl derivative with a good L.G. (like adding SOCl2) before converting it to an ester?
Sorry if this is confusing. When I go over answers, I try to come out with different ways I would think of the reaction occurring and explain why that explanation is false. However, I cannot come up with an explanation of why the cyclohexanol would not be dehydrated with the presence of protons in a solution.

Thank you in advance!

 

[0rgansm]

Could someone elaborate as to how the rate law is found is this GC problem?
.. I thought you couldn't even find the rate law without experimental data to begin with?
.. Even then, isn't it just the concentration of reactants? Why even bother looking at the slow step when the balanced equation is given?

 

[Dentoni]

Hi Dr. Romano and Nancy... In question # 22 organic chemistry destroyer 2012. Why did they not use PCC instead to oxidize? Thank you for help

 

[DAT Destroyer]

Hello,
I am slightly confused for OG #133.
So the answer is that all of them produce that certain product. My question is when adding Acetic acid, H3O+, why is it that we still get the acetic acid attacking the cyclohexanol and not having dehydration occur and forming a cation? Wouldn't the acetic acid have to be converted to a carbonyl derivative with a good L.G. (like adding SOCl2) before converting it to an ester?
Sorry if this is confusing. When I go over answers, I try to come out with different ways I would think of the reaction occurring and explain why that explanation is false. However, I cannot come up with an explanation of why the cyclohexanol would not be dehydrated with the presence of protons in a solution.

Thank you in advance!

An acid reacts with an alcohol in a classic ESTERIFICATION reaction. In esterification, the first step is protonation , but we protonate the carbonyl oxygen. . Why ? This is the site of greatest ELECTRON DENSITY.....next, the alcohol comes in as a nucleophile for the attack. As you can see,,,,,this mechanism is quite different from the one you suggested. As a general rule....always protonate a carbonyl O over an alcohol O.

I hope this helps.

If not, consult any standard Organic text for the Fischer Esterification mechanism.

 

[Denizen]

On organic chemistry question 62, by what mechanism is the final product (second reaction) produced? I don't believe I've seen this reaction between an enamine and an alkyl halide before.

Also, I apologize for posting a photo earlier. I am glad it was removed and will never do it again.

 

[DAT Destroyer]

On organic chemistry question 62, by what mechanism is the final product (second reaction) produced? I don't believe I've seen this reaction between an enamine and an alkyl halide before.

Also, I apologize for posting a photo earlier. I am glad it was removed and will never do it again.

This is a very important reaction. It is the alkylation of an enamine !!! We use it to add an alkyl group or even other functionalities to an enamine which is then hydrolyzed to form an alpha ketone. The enamine acts as a NUCLEOPHILE by attacking the alpha Carbon....the one with the halogen on it.....to form an alkylated iminium salt which is further hydrolyzed. Google the worked out reaction or see it written out in any text.


Hope this helps.

Dr. Romano

 

[Dentoni]

In question # 22 organic chemistry destroyer 2012. Why did they not use PCC instead of K2Cr2O7 to oxidize?

 

[Mrhyde]

In question # 22 organic chemistry destroyer 2012. Why did they not use PCC instead of K2Cr2O7 to oxidize?

I dont have the 2012 version but maybe this would help you:

PCC is a weak oxidizing agent
The weak one (PCC):
on a primary = turn OH to an aldehyde
on a secondary = turn OH to Ketone ( just like a strong one would)
on a tertiary = no reaction

K2Cr2O7 (chromic acid variants, just look for the Cr2O7 part) , Kmno4, and Ag2O - are all strong oxidizing agents.
The strong ones:
on a primary = turn OH to carboxylic acid
on a secondary = turn OH to Ketone ( just like a weak one would)
on a tertiary = no reaction

 

[SmilezAllDay]

Hey,

looking through the destroyer and I was wondering, for the bio lab techniques do we have to know anything about bacteria cultures... or ELISA technique for antibodies, EKGs, etc..... ? Just not sure how much they test on Lab procedures. I see in the destroyer.. microarray, N,S,W Blots, electrophoresis, PCR .... a bunch of really great stuff, but there are more lab techniques that are not in the book. Any advice would help.

The destroyer is unreal. Just trying to go above and beyond.

stay nerdy my friends

 

[Denizen]

^ I have also been curious about the extent to which bio lab stuff is tested on the DAT. I have done a few CliffsAP practice tests now, and they cover some very basic lab stuff that is really more concept-based, so I go over them. I haven't started the bio questions in Destroyer yet, but I am sure they're tough.

Dr. Romano, I am having trouble carrying out an accurate estimation to solve general chemistry problem #140. I understand how to set the problem up, and have become pretty good at playing with numbers and estimating, but this one is giving me trouble. Any advice would be appreciated!

 

[SmilezAllDay]

^ I have also been curious about the extent to which bio lab stuff is tested on the DAT. I have done a few CliffsAP practice tests now, and they cover some very basic lab stuff that is really more concept-based, so I go over them. I haven't started the bio questions in Destroyer yet, but I am sure they're tough.

Dr. Romano, I am having trouble carrying out an accurate estimation to solve general chemistry problem #140. I understand how to set the problem up, and have become pretty good at playing with numbers and estimating, but this one is giving me trouble. Any advice would be appreciated!

Dude! Make sure you read everything in the bio destroyer, I'm talking everything! answer key also.. Good luck

 

[Denizen]

For org. chem. #126, in choice B, how can you convert a carboxylic acid (less reactive) directly to an ester (more reactive)? This doesn't follow from what I learned in Chad's videos.

 

[Mrhyde]

For org. chem. #126, in choice B, how can you convert a carboxylic acid (less reactive) directly to an ester (more reactive)? This doesn't follow from what I learned in Chad's videos.

I only have the new version of DAT destroyer and your question is coming from an older version since number 126 has nothing to do with this question in my book. But let me see if I can help. To go from a carobxylic acid to an ester , an easy way to do this is through fischer esterification , here is a nice picture:
http://11452-presscdn-0-51.pagely.netdna-cdn.com/wp-content/uploads/2012/01/1-header55.png

but basically you have a COOH then you add R-OH/H+ ---> now you have COOR

 

[Dentoni]

For GC: I have two questions: 1) why does symmetry make the molecule non-polar?
2) In destroyer: Cu + AgNO3 -----> Cu (NO3)2 + Ag
Cu is oxidized and at the same time it's called "reducing reagent". I thought Cu (NO3)2 because we should not call the element reducing agent.

Your help is appreciated. Thank you Dr. Romano

 

[Denizen]

For GC: I have two questions: 1) why does symmetry make the molecule non-polar?
2) In destroyer: Cu + AgNO3 -----> Cu (NO3)2 + Ag
Cu is oxidized and at the same time it's called "reducing reagent". I thought Cu (NO3)2 because we should not call the element reducing agent.

Your help is appreciated. Thank you Dr. Romano

Hi Dentoni. 1) I think a better way to think of it might be radial symmetry makes the molecule non-polar, if you're familiar with the term. Also, if you have taken physics, you'll be familiar with the concept of vector addition. If you think about each bond dipole as a vector, and when you add them they all cancel each other out, that is when a molecule is non-polar. Take NH3, for example though, which may look symmetrical drawn out on a page; if you add the vectors you will find they result in a net dipole. 2) Simply remember: if something is oxidized, it's the reducing agent. If something is reduced, it's the oxidizing agent (opposites).

—

Thanks for the reply Mrhyde. I forgot about that reaction; I'll have to take a second look at that!

 

[Dentoni]

Hi Dentoni. 1) I think a better way to think of it might be radial symmetry makes the molecule non-polar, if you're familiar with the term. Also, if you have taken physics, you'll be familiar with the concept of vector addition. If you think about each bond dipole as a vector, and when you add them they all cancel each other out, that is when a molecule is non-polar. Take NH3, for example though, which may look symmetrical drawn out on a page; if you add the vectors you will find they result in a net dipole. 2) Simply remember: if something is oxidized, it's the reducing agent. If something is reduced, it's the oxidizing agent (opposites).

—

Thanks for the reply Mrhyde. I forgot about that reaction; I'll have to take a second look at that!

Hi Thank you....I thought Cu (NO3)2 would be a reducing agent. Because for some reason, I remember that we are not allowed to call the same element "Cu" a reducing agent because its not an agent, its an element and that Cu (NO3) is the answer.

 

[Alpha Centauri]

Doc Romano, or anyone else

Bio Destroyer number 277

This statement is false: An amino acid enters the cytoplasm from a t-rna molecule and first goes to the ribosome

Can someone clear up why this is false? Is it supposed to be entering the cytoplasm via an m-rna? Are m-rna's considered amino acids? This is a trivial question I think but I just want to know for the sake of knowing, and I am confused on the wording

 

[Denizen]

Hi Thank you....I thought Cu (NO3)2 would be a reducing agent. Because for some reason, I remember that we are not allowed to call the same element "Cu" a reducing agent because its not an agent, its an element and that Cu (NO3) is the answer.

That's right, when you're talking about an "agent," you most refer to the whole molecule. When you are saying what is reduced or oxidized, though, it's okay to say either the molecule or the individual element (e.g. Na was reduced).

Rich, I must have a different version of DAT Destroyer than you. The question itself I'm a bit confused about, but mRNA's are definitely not amino acids. DNA and RNA are nucleic acids, amino acids are the building blocks of proteins. DNA is transcribed to mRNA in the nucleus, exits through a nuclear pore, and then is read by a ribosome which creates a chain of amino acids (i.e. a protein). tRNA's are what carry amino acids to the ribosome to be added to the growing chain.

 

[emhl123]

For OC #255 in 2016 Destroyer...
I thought t-butyl was too bulky of a base to remove the double alpha proton between two ketones. How do know when/if t-butyl is able to remove the most acidic proton?

 

[emhl123]

2016 Destroyer OC #259. Why does the acyl halide add to the amine and not the benzene ring? Thanks in advance!

 

[Alikhan9]

For OC #255 in 2016 Destroyer...
I thought t-butyl was too bulky of a base to remove the double alpha proton between two ketones. How do know when/if t-butyl is able to remove the most acidic proton?

Tert-butyl is to much of a bulky base to perform a backside attack hence the only function would be as a base to remove a proton yes in terms of what aplha proton it can remove it removes the one in which the least substituted benzene is formed

 

[Mrhyde]

2016 Destroyer OC #259. Why does the acyl halide add to the amine and not the benzene ring? Thanks in advance!

Well the Acyl Halide will not react in this EAS reaction for 2 reasons. First reason is , there is no lewis acid catalyst under it to make it react in a EAS fasion with the benzene { quick note: even if there was a lewis acid catalysist it wont react in EAS and it would just make the amine charged... its a NH2 exception with lewis acids and the other expetion is with H2sO4 } so then the 2nd reason is that acyl halide CAN react with amine through the carboxylic acid derivatives chain where we have the the acyl chloride as number one in the hill and amine as number 4 so it will work and we will just remove one H off of the amine and attach the acyl chloride by removing the Cl which makes us the side product of HCl

 

[P0W3RL1FT3R]

2016 Destroyer GC #180

using the CARDIO mnemonic I ended up with the wrong answer. Is this mnemonic strictly for OC or something?

 

[Mrhyde]

2016 Destroyer GC #180

using the CARDIO mnemonic I ended up with the wrong answer. Is this mnemonic strictly for OC or something?

What was your wrong answer and what was your reasoning for picking it ?

 

[P0W3RL1FT3R]

What was your wrong answer and what was your reasoning for picking it ?

The weakest base would have the least negative charge, bigger atom, etc. (Chads approach taught in OC).
The correct answer had the weakest base with a negative charge, which I had thought was a dead giveaway that it'd be the stronger base.

the Destroyer explanation made total sense, but I had always thought using the CARDIO mnemonic when comparing bases was best. Maybe its only for OC?

 

[Mrhyde]

The weakest base would have the least negative charge, bigger atom, etc. (Chads approach taught in OC).
The correct answer had the weakest base with a negative charge, which I had thought was a dead giveaway that it'd be the stronger base.

the Destroyer explanation made total sense, but I had always thought using the CARDIO mnemonic when comparing bases was best. Maybe its only for OC?

Honestly for me personally I think that method might only apply for structures not single molecules. So for me when I tried it , I still knew the answer from memorizing a PKA table from OC which still applied here.

 

[FutureDDS_11]

2016 Destroyer GC #247 and #251 can you please explain the problems to me a little bit further and how to approach solving them?

 

[zyzzbruh]

Hello,

I'm a bit confused about #57 in the 2016 DAT Destroyer, Biology section.

I had thought any peptide hormone would bind to a target cells receptor protein, which dissociates a G-protein, activating adenylyl cyclase, which converts ATP to cAMP, etc. etc.

why is this limited to epinephrine? why couldn't another peptide hormone such as hGH trigger the same response?

thanks!

 

[Sandel]

Hi Dr. Romano,
For the 2016 DAT Destroyer, Biology section on #139

Question: Match the hormone to its function.
The answer says its E (all are correct) but your explanation states only what letter C.) epinephrine does and it contradicts the question choices because letter A.) says cortisol increases blood glucose but your answer explanation says epinephrine increases blood glucose. Can you please explain if and why each letter choice is correct? Thank you!!

 

[jws95]

For Gen Chem #83 on the 2016 edition, why wouldn't the two half reactions get balanced (multiply the top by 3 and bottom reaction by 2) before you find the total cell voltage?

 

[DMikes]

Hi Dr. Romano,
For the 2016 DAT Destroyer, Biology section on #139

Question: Match the hormone to its function.
The answer says its E (all are correct) but your explanation states only what letter C.) epinephrine does and it contradicts the question choices because letter A.) says cortisol increases blood glucose but your answer explanation says epinephrine increases blood glucose. Can you please explain if and why each letter choice is correct? Thank you!!

The answer is just listing all the things that epinephrine does. Hormones can serve many purposes in the body.

It doesn't talk about any of the others, but rest assured all the others are correct.

 

[DMikes]

#548 2016 edition Bio. Pretty generic question. I understand the whole size exclusion chromatography idea, but what is the cutoff for when molecular weight differences matter and will appear as separate bands? Is there one? ~ 5,000?

Thanks!

 

[DMikes]

Hello,

I'm a bit confused about #57 in the 2016 DAT Destroyer, Biology section.

I had thought any peptide hormone would bind to a target cells receptor protein, which dissociates a G-protein, activating adenylyl cyclase, which converts ATP to cAMP, etc. etc.

why is this limited to epinephrine? why couldn't another peptide hormone such as hGH trigger the same response?

thanks!

epinephrine is an amino acid derived hormone I believe.

 

[DAT Destroyer]

Hi Dr. Romano,
For the 2016 DAT Destroyer, Biology section on #139

Question: Match the hormone to its function.
The answer says its E (all are correct) but your explanation states only what letter C.) epinephrine does and it contradicts the question choices because letter A.) says cortisol increases blood glucose but your answer explanation says epinephrine increases blood glucose. Can you please explain if and why each letter choice is correct? Thank you!!

They both increase blood glucose. Epinephrine increases blood glucose when it gets too low. It stimulates the breakdown of liver glycogen.
Cortisol increases blood glucose during stress and when blood sugar decreases.

Hope this helps.

 

[Mrhyde]

Dat Destroyer - organic chem - number 141.

Are All Trans going to be "IR inactive" .... and also if choice A has symmetry then how can choice D not have symmetry ? I can imagine folding choice D (Cis) perfectly in half and get a mirror image so how is there no symmetry ? Choice A (trans) I can imagine folding vertically so I see that symmetry .

 

[Mrhyde]

My next question is on number 144 - organic chem- DAT destroyer . Nominclature
Can anyone verify this logic?
I have always thought that if all else was equal we would take the path with the least number of substituents for simplicity .
But here when all else is equal the answer explanation says to choose the path with the MOST substituents? I don't understand why we would prefer a longer more complicated answer when we could go with saying just isopropyl ? I chose A but was wrong with the answer being the longer D

 

[DentalNucleicAcid]

My next question is on number 144 - organic chem- DAT destroyer . Nominclature
Can anyone verify this logic?
I have always thought that if all else was equal we would take the path with the least number of substituents for simplicity .
But here when all else is equal the answer explanation says to choose the path with the MOST substituents? I don't understand why we would prefer a longer more complicated answer when we could go with saying just isopropyl ? I chose A but was wrong with the answer being the longer D

No, if all else is equal, you would take the path with the most number of substituents. Recall that chad said that the goal of nomenclature was to "make the longest word in the world", right? It makes sense why you want to have more substituents than less because if you have more then it'll be easier to name the individual groups. If you have less substituents, then it might become hard to name them because they'd have so many things attached to them.

 

[Mrhyde]

No, if all else is equal, you would take the path with the most number of substituents. Recall that chad said that the goal of nomenclature was to "make the longest word in the world", right? It makes sense why you want to have more substituents than less because if you have more then it'll be easier to name the individual groups. If you have less substituents, then it might become hard to name them because they'd have so many things attached to them.

I forgot Chad said that lol Thank you so much ! I will remember it now

But then will we ever use the short words like "tert-butyl " for example or will they always just be full iupac since we can describe tert-butyl by saying (dimethylethyl)

 

[DentalNucleicAcid]

I forgot Chad said that lol Thank you so much ! I will remember it now

But then will we ever use the short words like "tert-butyl " for example or will they always just be full iupac since we can describe tert-butyl by saying (dimethylethyl)

Yeah you could, in cases where there is only one path to get the longest chain. It just so happened that in this particular case, if you wanted to say isopropyl, then you'd be using a route with less substituents, which is not what we want. Here's an example:

In this case we can say "tert-butyl" because using it as part of our parent chain wouldn't give us a longer chain- there's a way to get a longer chain without including parts of the t-butyl in our chain. It would be called 5-tert-butyl-3-ethyl-2-octanol

 

[Mrhyde]

Yeah you could, in cases where there is only one path to get the longest chain. It just so happened that in this particular case, if you wanted to say isopropyl, then you'd be using a route with less substituents, which is not what we want. Here's an example:
View attachment 205646
In this case we can say "tert-butyl" because using it as part of our parent chain wouldn't give us a longer chain- there's a way to get a longer chain without including parts of the t-butyl in our chain. It would be called 5-tert-butyl-3-ethyl-2-octanol

"because using it as part of our parent chain wouldn't give us a longer chain" That's the key , Thank you for taking the time to draw that I appreciate it and understand it now.

 

[emhl123]

For #475 biology, the solution says that kinetochores of sister chromatids are pulled to opposite poles during metaphase. I thought this step happened during anaphase?

 

[deleted738762]

delete

 

[Mrhyde]

For #475 biology, the solution says that kinetochores of sister chromatids are pulled to opposite poles during metaphase. I thought this step happened during anaphase?

Yes that has to be a small incorrect addition. but everything else about the question seems correct.

In metaphase the microtubules of the spindle have attached and the chromosomes have lined up on the metaphase plate. During Anaphase , the sister chromatids are pulled apart and move toward opposite poles of the cell.

 

[DAT Destroyer]

Dat Destroyer - organic chem - number 141.

Are All Trans going to be "IR inactive" .... and also if choice A has symmetry then how can choice D not have symmetry ? I can imagine folding choice D (Cis) perfectly in half and get a mirror image so how is there no symmetry ? Choice A (trans) I can imagine folding vertically so I see that symmetry .

You are missing the point......Don't focus on symmetry , but think DIPOLE. The Cis isomer has a dipole, hence we get a reasonably nice signal for that particular functional group. In the trans isomer, if the groups are the SAME.......we have a molecule with no dipole, hence no signal for that particular functional group. If the groups were DIFFERENT, we would get a signal, but likely very very weak. Remember.....In IR, we are bending and stretching bonds, causing them to vibrate,,,,,,the molecule needs to have a dipole to detect any differences in stretching or bending vibrations.

I hope this helps.

Dr. Romano

 

[DAT Destroyer]

My next question is on number 144 - organic chem- DAT destroyer . Nominclature
Can anyone verify this logic?
I have always thought that if all else was equal we would take the path with the least number of substituents for simplicity .
But here when all else is equal the answer explanation says to choose the path with the MOST substituents? I don't understand why we would prefer a longer more complicated answer when we could go with saying just isopropyl ? I chose A but was wrong with the answer being the longer D

LOL.....Pardon my mirth at this question. I give this the GOLD star !!!!!!! The IUPAC committee makes up the rules of nomenclature, much like the ADA makes up the rules for the DAT exam !!!!! You must learn and follow the rules !!!!!!!

Dr. Romano

 

[amaghsou]

Hi Dr. Romano,

I was confused regarding one of the questions in the Destroyer book and wanted a clarification.

Question 67 on the Organic section has a choice of a benzene ring having a COOH group attached with a NO2 group. I wanted to know how this was possible since Carboxylic Acids and Nitro groups are typically meta-directors.