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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[Alikhan9]

Well it doesnt matter what you have attached before but what you attach after

 

[Mrhyde]

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

HAHAHAHa Thanks for the help all the time ! I would like that gold star

 

[deleted738762]

#53. Why is it 6-flourobicyclo [3.2.1] octane? The number in the parenthesis indicate the number of carbons between the bridgehead. So shouldn't it be [4.3.2.1] also why does it go from largest to smallest number in parenthesis.

 

[deleted738762]

#58 how is I chiral in the answer key. It has 2 hydrogens bonded next to it. Also why couldn't you chlorinate the top methyl group?
Thanks

 

[deleted738762]

#67. Why can't the NH2 in amide become the imine?

 

[DAT Destroyer]

#53. Why is it 6-flourobicyclo [3.2.1] octane? The number in the parenthesis indicate the number of carbons between the bridgehead. So shouldn't it be [4.3.2.1] also why does it go from largest to smallest number in parenthesis.

First off......all bicyclo compounds have 3 numbers in the brackets NOT 4. Number the first bridgehead carbon as 1 as shown in the solution.....then work yourself to the other BRIDGEHEAD carbon by the LONGEST path !!!! In descending order, you will note 4, 3 and 1 carbon atoms between these bridgeheads. . I hope this helps.....If not, the David Klein text has a few very clear examples that you can review before trying this problem again.

Dr. Romano

 

[Mrhyde]

#67. Why can't the NH2 in amide become the imine?

like the answer explanation says the reason that side cant become the imine is because that NH2 is directly part of the carbonyll making that part considered a amide. The amide will be stable because of resonance . The amide would be R-C-O-Nh2 ... So we know we cant use the C-O-Nh2 part so we have to use the "R" part which in this case the "R" part is the NH2-Nh remaining section

 

[DCG anonymous]

Why must you convert to mols in order to find heat using q=mc(dH)?

Thanks in advance

 

[DAT Destroyer]

#58 how is I chiral in the answer key. It has 2 hydrogens bonded next to it. Also why couldn't you chlorinate the top methyl group?
Thanks

Most kids miss this one.....The carbon bearing the Chlorine is not chiral.....BUT the one next to is !!!!!!! Look at all the carbons....The two methyl groups are EQUIVALENT . Re-do this problem......you have missed two important concepts.

Dr. Romano

 

[deleted738762]

like the answer explanation says the reason that side cant become the imine is because that NH2 is directly part of the carbonyll making that part considered a amide. The amide will be stable because of resonance . The amide would be R-C-O-Nh2 ... So we know we cant use the C-O-Nh2 part so we have to use the "R" part which in this case the "R" part is the NH2-Nh remaining section

Thanks I was covering the bottom answer didn't see lol

 

[deleted738762]

Most kids miss this one.....The carbon bearing the Chlorine is not chiral.....BUT the one next to is !!!!!!! Look at all the carbons....The two methyl groups are EQUIVALENT . Re-do this problem......you have missed two important concepts.

Dr. Romano

DAMN THAT WAS TRICKY lol

 

[DAT Destroyer]

#67. Why can't the NH2 in amide become the imine?

Not a chance......the amide has resonance and will not be a very good nucleophile . Be careful here......you needed to examine BOTH ends, and make a decision as to which side of the reagent would be the nucleophile against the carbonyl group.

Hope this helps.

Dr. Romano

 

[DAT Destroyer]

DAMN THAT WAS TRICKY lol

Yes......Tricky is nice.....but when the DAT comes...be ready to KICK ASS !!!!!

 

[Ineed2getin]

Page 11 dat destroyer(o chem )# 4. It is asking for the conjugate base. Why wouldn't the answer be C? Can't NH2 be deprotonated?


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[Ineed2getin]

Dat destroyer page 13 ochem, #13. Why is choice d the compound that has the most acidic proton. What makes a compound have an acidic proton?


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[amaghsou]

Well it doesnt matter what you have attached before but what you attach after

Im not sure if I quite understood what you meant. All I am asking is regarding the groups. Shouldn't either the Nitro group or Carboxylic Acid group be Meta to each other and not Para, like the picture I have attached?

Thank you

 

[Mrhyde]

Dat destroyer page 13 ochem, #13. Why is choice d the compound that has the most acidic proton. What makes a compound have an acidic proton?


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I mean you would normally go about this problem by knowing some common PKA values and having those memorized. But this problem was a little tricky because if you went by PKA values you would probably assume answer C since COOH is around Pka 4 . But this problem was meant to teach you that if you see a Hydrogen directly attached to a carbonyl carbon that H would be extremely acidic and have a pka of about -6 , Which will certainly beat a pka of 4 from the COOH

 

[Mrhyde]

Page 11 dat destroyer(o chem )# 4. It is asking for the conjugate base. Why wouldn't the answer be C? Can't NH2 be deprotonated?


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Again we go to some common PKA values. So NH2 has a PKA of around 35 which means its a really stable base. while OH has a pka of around 17 which means its really acidic so , which would loose an H easier , something stable (base) or something less stable (acid). So we go with OH

 

[FutureDDS_11]

Hello,
Can you please explain the reagents' general mechanism for #290 Organic Chem 2016?

 

[Ineed2getin]

I mean you would normally go about this problem by knowing some common PKA values and having those memorized. But this problem was a little tricky because if you went by PKA values you would probably assume answer C since COOH is around Pka 4 . But this problem was meant to teach you that if you see a Hydrogen directly attached to a carbonyl carbon that H would be extremely acidic and have a pka of about -6 , Which will certainly beat a pka of 4 from the COOH

Thank you it makes a lot of sense! Do u have a list of common pka values that I should have memorize for the Dat?


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[Mrhyde]

Thank you it makes a lot of sense! Do u have a list of common pka values that I should have memorize for the Dat?


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Yes I do. I printed this one out and made notes, Here is the link to the original list:
http://11452-presscdn-0-51.pagely.netdna-cdn.com/wp-content/uploads/2010/06/1-pkas.png

but just to let you know I made a small amount of additions. I added to this list the compound phenol and that phenol is 10 and I added to this list the compound amide , and that Amide is 15 and I changed waters pka to 15.7 .......... Theres also a bunch of small notes I added to make the list really easy to memorize, one of my small notes was noticing that all the compounds with sulfur on this list are all combinations of the number 3 and the number 1 ... also I added that when you hit HCl ,HBr, and HI , you dont need to memorize those pkas because of the trend you should memorize that as you increase in size you have a better ability to stabilize a negative charge so you are more acidic , so by just looking at the periodic table you could figure out where those rank. But I would memorize HF since its not surrounded with the others.

Also just to let you know , you dont have to memorize this list, I am sure other people have other ways but for me personally I rather just memorize this and know for sure then try to think of a lot of rules for ranking and possibly make a silly mistake

 

[deleted738762]

Yes I do. I printed this one out and made notes, Here is the link to the original list:
http://11452-presscdn-0-51.pagely.netdna-cdn.com/wp-content/uploads/2010/06/1-pkas.png

but just to let you know I made a small amount of additions. I added to this list the compound phenol and that phenol is 10 and I added to this list the compound amide , and that Amide is 15 and I changed waters pka to 15.7 .......... Theres also a bunch of small notes I added to make the list really easy to memorize, one of my small notes was noticing that all the compounds with sulfur on this list are all combinations of the number 3 and the number 1 ... also I added that when you hit HCl ,HBr, and HI , you dont need to memorize those pkas because of the trend you should memorize that as you increase in size you have a better ability to stabilize a negative charge so you are more acidic , so by just looking at the periodic table you could figure out where those rank. But I would memorize HF since its not surrounded with the others.

Also just to let you know , you dont have to memorize this list, I am sure other people have other ways but for me personally I rather just memorize this and know for sure then try to think of a lot of rules for ranking and possibly make a silly mistake

I never memorized pKa's ever. Just find the most stable conjugate base. I used klein so it's second nature to just look at the conjugate base for me, but if this biochem it would be different.

 

[Mrhyde]

I never memorized pKa's ever. Just find the most stable conjugate base. I used klein so it's second nature to just look at the conjugate base for me, but if this biochem it would be different.

Yep like I said other people have other ways but for me personally I rather just memorize this then risk maybe a mess up on the rules from a dumb mistake .... but I still know and recommend to know the rules

 

[emhl123]

Could someone clear this up for me? Cardiac output is the volume of blood pumped by the ventricle (per minute). Stroke volume is the volume of blood pumped out of the heart with each beat. I am a little confused with these two terms, and seem to get them mixed up.

 

[P0W3RL1FT3R]

#277 2016 Destroyer, general chemistry

kw=[h30][oh] or kw=x^2

one we find x, why do we assume "x" is [h3o] opposed to [OH]?

i found the pOH from "x," which led me to a pH of 7.4

thanks

 

[DrNoCavity]

Is TCA cycle substrate level phosphorylation?

 

[kimball]

Is TCA cycle substrate level phosphorylation?

Yep its substrate, oxidative phosphorylation= ATP is formed (phosphorylation of ADP-->ATP) but the energy used to add the phosphate group to ADP is taken from gradients created by the electron transport chain (done by using NADH and FADH2 the main products of TCA but not where the actual ATP is formed). (easy way to remember: oxygen is the final electron acceptor of the chain= Oxidative).
Substrate level= energy to phosphorylate the ATP is taken from a substrate (like citrate in TCA cycle) TCA produces 1 ATP per turn using this

 

[Charles_Darwin]

For those who have done both DAT destroyer and Math destroyer:

Are they both on the same level of difficulty? I've bought both, but am currently working through the destroyer and plan on doing 1 math destroyer test a day after. I know Math destroyer is supposed to be timed practice- will understanding everything in the QR part of DAT destroyer prepare me well for math destroyer?

 

[zyzzbruh]

#28 GC 2016

Is there a key word to this problem? Or is it when the molarity is below/above a certain threshold?
I understand if a solution is dilute it will draw the pH closer to 7, but when do we know it's dilute?

For a hypothetical question like... "What would be the approximate pH of a 1x10^-8 M HCl solution?"
I assume we go through the process of adding (1x10^-8)+(1x10^-7) to get a pH ~6.9
... if i even did that right.. lol

Just confused as to when we can simply take the -log of the strong monoprotic acid, opposed to taking into account the H+ from water.

Thanks!

 

[kimball]

#28 GC 2016

Is there a key word to this problem? Or is it when the molarity is below/above a certain threshold?
I understand if a solution is dilute it will draw the pH closer to 7, but when do we know it's dilute?

For a hypothetical question like... "What would be the approximate pH of a 1x10^-8 M HCl solution?"
I assume we go through the process of adding (1x10^-8)+(1x10^-7) to get a pH ~6.9
... if i even did that right.. lol

Just confused as to when we can simply take the -log of the strong monoprotic acid, opposed to taking into account the H+ from water.

Thanks!

Yeah you are on the right track, you know that the water eq. concentration is 1 x 10^-14, with the H+ as 1x10^-7, the error is not recognizing that the acid concentration you are adding is extremely small compared equilibrium concentration of H+ of water. At that point the equilibrium concentration of H+ of water becomes the most significant factor in calculating the pH.
The rule: The contribution of OH- and H+ ions to an aqueous solution from the autoionization of water can be neglected only if the concentration of the acid or base is significantly greater than 10^-7.
Your Example: if you are calculating the pH of a 1x10^-8 M solution of HCl, you have to recognize that 1x10^-8 is ten times smaller than 1x10^-7 (eq conc. H+ in water) at the pH is actually 7 still
Kw= [H3O+] [OH-]= [x+(1x10^-8](x)= 10^-14
solving for x: x= 9.5 x10^-8
[H+ total]= 9.5 x10^-8 + 1x10^-8= 1.05 x10^-7 (notice slightly less than normal value of H+ in water)
so then for pH you would calculate pH= -log(1.05 x10^-7)= 6.98

a solution of 1x10^-12 H+ from HCL you are essentially adding an extremely insignificant amount of H+ relative to the water, meaning the pH would have to stay 7.

 

[Mrhyde]

- Even though I got number 95 correct on the Organic DAT Destroyer pg. 31 , -----> I know that the NBS removes off a benzylic hydrogen and replaces it with a BR but what if we had this :
https://s31.postimg.org/xwpi1b8bv/question_1.png
Would the BR attach to the first available benzylic hydrogen OR would it prefer the tertiary position even though its not the first hydrogen closest to the benzene ?

 

[WolfsBane]

Im not sure if I quite understood what you meant. All I am asking is regarding the groups. Shouldn't either the Nitro group or Carboxylic Acid group be Meta to each other and not Para, like the picture I have attached?

Thank you

 

[WolfsBane]

The way you would do this is you would a carbonyl then us HOCH2CH2OH TO protect it and add the nitro group Para as it now becomes a alkyl group which is a o,p director... then use h+ to get it back to the carbonyl, and finally, we'do use sodium dichromate to turn the carbonyl into a COOH and it would be Para to the nitro group!!

 

[asdf99]

#97 OC 2016

Hey everyone,

This questions asks which rxn can yield an alkene. One of the rxns shows a tertiary halide with methanol. Why is this not a possible answer? Wouldn't E1 and Sn1 be happening ?

 

[DAT Destroyer]

#97 OC 2016

Hey everyone,

This questions asks which rxn can yield an alkene. One of the rxns shows a tertiary halide with methanol. Why is this not a possible answer? Wouldn't E1 and Sn1 be happening ?

Indeed, Sn1 and E1 always compete, however there was no heat. Without the heat and with such a moderate nucleophile, Sn1 product predominates. Remember......BOTH mechanisms are operating, but heating will always favor the elimination process.

Hope this helps.

Dr. Romano

 

[asdf99]

Thank you Dr. Romano

 

[DAT Destroyer]

#58 how is I chiral in the answer key. It has 2 hydrogens bonded next to it. Also why couldn't you chlorinate the top methyl group?
Thanks

This is an important problem, and you have missed two key concepts. You need to look at the ENTIRE molecule.......Product #1 is chiral , at the second carbon !!!! The carbon with the chlorine is not chiral, that is true,,,,but C2 is chiral !!! In the molecule 2-methylbutane, BOTH methyls are equivalent, thus either can be chlorinated to yield the same monochlorination product.

Hope this helps.

Dr. Romano

 

[DAT Destroyer]

- Even though I got number 95 correct on the Organic DAT Destroyer pg. 31 , -----> I know that the NBS removes off a benzylic hydrogen and replaces it with a BR but what if we had this :
https://s31.postimg.org/xwpi1b8bv/question_1.png
Would the BR attach to the first available benzylic hydrogen OR would it prefer the tertiary position even though its not the first hydrogen closest to the benzene ?

Studies have shown that a secondary benzylic hydrogen is easier to remove than that of a tertiary. This is called bond dissociation energy. This translates into STABILITY........ The bromine would prefer to abstract the BENZYLIC hydrogen over the tertiary.

Hope this helps.

Dr. Romano

 

[DCG anonymous]

Has Gen Chem #300 been answered on here? I can't find it..

How come the Ksp for magnesium phosphate is equal to [Mg2+]^2 [PO43-]^2 ? I thought coefficients from equilibrium went into ksp as coefficients as well as exponents?

Thanks

 

[WheatLom]

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.

To synthesize this product.

1) Benzene treated with Methylchloride (CHCl3)/AlCl3 this gives Toluene process called Alkylation. Benzene with a methyl group. This is an Ortho Para director because it is an activator.

2) Treat Toluene with HNO3 and H2SO4 to give us Ortho-Nitrotoluene.

3) We then oxidize the methyl group with KMnO4 (potassium permanganate.) This yields a carboxylic acid. Remember that you need at least 1 benzylic hydrogen to do this.

done- final product is o-Nitrobenzoic acid.


Hope this helps. My first post ever. Helping someone out. I just reviewed this today for my DAT.

 

[deleted738762]

Biology Question #46.
The answer was analogous structures.

However, I thought parallel evolution is when two species diverge from a common ancestor, and then those two species evolve in a similar way parallel to each other afterwards. Since it's a common ancestor I thought it would be homologous.

I noticed the question states in separate lineages, but still does that no go against the definition of parallel evolution? Shouldn't it be called convergent evolution in the question.

Thanks for any clarity.

 

[deleted738762]

BUMP HELP ME

 

[emhl123]

Biology #90
I understand that ABO blood group is considered an example of multiple alleles, but would it also be correct to say that ABO blood group is an example of polygenic inheritance?

 

[merPda]

OC #291
Hi Dr.Romano,
The hydrazine reduces a carbonyl to methyl group, then in this question, shouldn't the cyclic structure remain in the final product? How are the N-C bonds cleaved?

Thanks so much!

 

[DAT Destroyer]

Biology Question #46.
The answer was analogous structures.

However, I thought parallel evolution is when two species diverge from a common ancestor, and then those two species evolve in a similar way parallel to each other afterwards. Since it's a common ancestor I thought it would be homologous.

I noticed the question states in separate lineages, but still does that no go against the definition of parallel evolution? Shouldn't it be called convergent evolution in the question.

Thanks for any clarity.

Parallel evolution - is when 2 species have similar characteristics and have a common ancestor.

Convergent evolution -is when 2 species have similar characteristics, but did no come from the common ancestor.

Divergent evolution - is when species have different characteristics, but camw from the same ancestor.

Hope this helps.

 

[deleted738762]

Parallel evolution - is when 2 species have similar characteristics and have a common ancestor.

Convergent evolution -is when 2 species have similar characteristics, but did no come from the common ancestor.

Divergent evolution - is when species have different characteristics, but camw from the same ancestor.

Hope this helps.

Yea, I already said this. So if it's from a common ancestor then why is it analogous structures? Isn't analogous associated with an uncommon ancestor?

 

[deleted738762]

Bio question #184. Answer is C. External fertilization involves cooperative behavior leading to copulation. It it wrong because their is no cooperative behavior?

 

[DAT Destroyer]

OC #291
Hi Dr.Romano,
The hydrazine reduces a carbonyl to methyl group, then in this question, shouldn't the cyclic structure remain in the final product? How are the N-C bonds cleaved?

Thanks so much!

Hydrazine does indeed reduce a carbonyl group...BUT that is for aldehydes and ketones,,,,,This molecule is neither. This is called an IMIDE, and doesn't react the same way. The mechanism is fairly complex, and not needed for the DAT,,,,,But since you asked.....

Hope this helps

Dr. Romano

 

[DentalNucleicAcid]

Number 3 Chapter 12 Ochem Odyssey:
The question shows a conjugated ring with 14 carbons and it asks if it's aromatic, the answer says yes. This can't be a planar ring, right? I thought the rule was >7 carbon ring = nonplanar. The only reason I can think of that might justify this being planar is that it has a triple bond meaning that 4 carbons in a row are in a straight line so those 4 don't count toward assessing the number of carbons in the ring for aromaticity

 

[DAT Destroyer]

Number 3 Chapter 12 Ochem Odyssey:
The question shows a conjugated ring with 14 carbons and it asks if it's aromatic, the answer says yes. This can't be a planar ring, right? I thought the rule was >7 carbon ring = nonplanar. The only reason I can think of that might justify this being planar is that it has a triple bond meaning that 4 carbons in a row are in a straight line so those 4 don't count toward assessing the number of carbons in the ring for aromaticity
View attachment 206372

No.....A ring deviates out of planarity for many reasons. Consider Cyclooctatetraene...It has 8 pi electrons, but becomes non planar and tub-shaped to avoid being anti- aromatic. This molecule you are referencing is an annulene. Many annulenes are planar if and only if aromaticity is achieved. Thus a specie such as this having 14 pi electrons would be aromatic. Contrary to what you may have read in undergrad text books, the absolute planarity of a molecule is NOT required for aromaticity. , but aromaticity does decrease with decreasing planarity as exemplified with buckminsterfullerene. The bottom line is this...when dealing with large rings such as in problem 3, if you see conjugation, cyclic structure, and a Huckel number.....there is a very high probability the specie will be aromatic. A Google search of annulenes might interest you, or the Francis Carey text has wonderful examples as does text by Dr. Marc Loudon.

Hope this helps.

Dr. Romano