Official DAT Destroyer Q&A Thread

[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!

 

[akakakakak]

OCHEM OD Chap 2 #12 - Consider acetic acid, pKa = 4.34. When pH =2, which is present....please explain - thanks

 

[akakakakak]

also #23....aren't they both part of the ring? both aromatic...

 

[gambaboy]

I prefer to never use silly tricks , but rather understand the concept. This so called CARDIO rules breaks down often and has many exceptions. An electron withdrawing group such as NO2, COOH, Carbonyl, SO3H all increase the acidity of a molecule. These groups will withdraw electron density and STABILIZE the anion....thus render a molecule much less basic, but more acidic. Let us do a concrete example. Consider benzoic acid with an NO2 group and another benzoic acid with a OCH3 group. The nitrobenzoic is more acidic because after the loss of a proton, the ANION is able to be stabilized by the nitro group. This stabilization is reflected in the fact that the negative anion charge is spread out. Any Organic chem text will draw the resonance forms for you to see. The next thing we need to do is to examine the benzoic acid with the OCH3 group. There is some electron withdrawal by induction, but also a MUCH GREATER electron donating effect, by resonance. This will destabilize the anion. Thus....the anion will be less stabilized and hence acidity decreases. Bottom line......Groups like NO2, COOH, CHO, carbonyl, SO3H. CN all increase acidity by electron withdrawal.....groups like CH3, C2H5, R groups, OCH3, OC2H5, N-groups like NH2, OH groups increase basicity by destabilizing the anion.

Hope this helps.

Dr. Jim Romano

So I understand that EDG would increase basicity and that EWG would decrease basicity, but I'm still having a little trouble with applying this to the problem in question, #4 of Ochem 2015.

As you said in your example with benzoic acid with the OCH3 group, there would be "some electron withdrawal by induction, but also a MUCH GREATER electron donating effect, by resonance", and therefore the OCH3 would increase the basicity.
For answer choice D of this question, wouldn't the inclusion of the Oxygen group act similarly to the OCH3? It would have some electron withdrawal by induction, but be electron donating due to resonance and therefore increasing the basicity of the compound.

Thank you so much for all the help so far!

 

[hye340]

Hi for 2015 destroyer ochem problem 178 why isn't E a Newman projection?Thanks!!

 

[hye340]

for question 178 in destroyer 2015 ochem,why is E not a Newman projection

and for question 183 how do you get the Newman and turn it into a Fischer diagram,why does the ch3 point to the right instead of the left.Thanks

 

[DAT Destroyer]

for question 178 in destroyer 2015 ochem,why is E not a Newman projection

and for question 183 how do you get the Newman and turn it into a Fischer diagram,why does the ch3 point to the right instead of the left.Thanks

Choice E is indeed a Newman. The question asks for hexane......Choice E is 2,2-dimethylbutane. For a nice review on Newman structures, the text by David Klein is well written and should help you if needed.

Hope this helps

Dr. Jim Romano

 

[hye340]

Thanks Dr Romano
what about question 183?why is the methyl on the right side of the Fischer projection.the one converted from a Newman which is shown on the solution page

 

[DAT Destroyer]

Thanks Dr Romano
what about question 183?why is the methyl on the right side of the Fischer projection.the one converted from a Newman which is shown on the solution page

This is just a trick to get the correct stereochemistry. I reversed the two groups on the back carbon. Without models, it is tough to show you. However,,,,this trick will allow you to easily convert a Newman into a Fischer !!!! For the DAT,,,,,,knowing the R/S configuration off a Fischer is critical.....and being able to compare two molecules and determine their relationship. For example if one Fischer is RR and the other RS.....and all the atoms are in the same position..... we have a diastereomer pair. Also make sure that you can do R/S using dash and wedge 3D structures.

Hope this helps.

Dr. Jim Romano

 

[dentalstudent2021]

I know its really simple question. But when dividing numbers like 4.8/0.12 How would I do this without writing this in scientific notation. I try to usually do it in my head by moving decimals like 48/12 then adjusting decimals in the answer. any other way or easier method ? Thanks.

 

[DAT Destroyer]

I know its really simple question. But when multiplying numbers like 4.8/0.12 How would I do this without writing this in scientific notation. I try to usually do it in my head by moving decimals like 48/12 then adjusting decimals in the answer. any other way or easier method ? Thanks.

From what you wrote it's division not multiplication. 4.8/0.12 = 480/12. remember you you don't want to have a decimal in the denominator. you multiply both the denominator and numerator by 100 and you get: 480/12 next you always want to reduce the fraction. It's easy to see that they can both be reduced by 12. IAnd you get 40. If it's a multplication ( 4.8x0.12 ) It's useful to have the answer choices. You just multiply the last 2 digits of each number. 2x8 = 16. This means that the last digit of the answer has to be 6. It works almost all the time.

Hope this helps.

 

[doitfortheppl2016]

Question bout organic odyssey chapter 12 #25. You say that if NO2 or NH2 is on a benzene ring, no reaction occurs because the groups will react with the AlCl3. Is this the case only with AlCl3? I noticed that the same rule didn't apply when FeCl3 was used, like in question 23. Thank you

 

[DAT Destroyer]

Question bout organic odyssey chapter 12 #25. You say that if NO2 or NH2 is on a benzene ring, no reaction occurs because the groups will react with the AlCl3. Is this the case only with AlCl3? I noticed that the same rule didn't apply when FeCl3 was used, like in question 23. Thank you

doitfortheppl2016.
Great question ! Lewis acids have different strengths much like ordinary acids that you are more familiar with.. If a meta director such as CN, SO3H, NO2...or a SUPER activator group such as NH2 is present, the Friedel Craft alkylation and acylation fail miserably. It turns out that the reactions involving FeCl3 or FeBr3 do work. We can chlorinate nitrobenzene easily, but cannot directly methylate the molecule directly using a Friedel Crafts reaction. I The logic behind this is often the subject of debate in Organic Chemistry journals and advanced literature.

Hope this helps.

Dr. Jim Romano

 

[dentalstudent2021]

on this structure, the Carbon with lone pair is sp2 right ? since the lone pair is used in conjugation. And there is also an Hydrogen on the same carbon right ?(don't know why i got confused here)

Also, since 1.Sp2 2.planar. 3.cyclic +conjugated and 4. 4II electrons. this is a aromatic compound, right ?
Thanks.

 

[DAT Destroyer]

on this structure, the Carbon with lone pair is sp2 right ? since the lone pair is used in conjugation. And there is also an Hydrogen on the same carbon right ?(don't know why i got confused here)

Also, since 1.Sp2 2.planar. 3.cyclic +conjugated and 4. 4II electrons. this is a aromatic compound, right ?
Thanks.

Yes, you are correct. This is Aromatic anion. All carbons are sp2, it is completely conjugated, planar and has a Huckel number.

 

[dentalstudent2021]

for this question. can the structure in the red circle also be a product ?

 

[plusalpha]

for this question. can the structure in the red circle also be a product ?

Either way, it's the same exact compound you get (notice how it is a meso compound due to a line of symmetry)

 

[DAT Destroyer]

for this question. can the structure in the red circle also be a product ?

Yes. You will get cis product, both substituents may be pointing down or up.
Hope this helps.

 

[rak173]

Yes. You will get cis product, both substituents may be pointing down or up.
Hope this helps.

Are those both products same, just flipped on its the other side? Thank you.

 

[DAT Destroyer]

Are those both products same, just flipped on its the other side? Thank you.

Yes

 

[doitfortheppl2016]

Question about Organic odyssey chapter 5 #19
Isnt (CH3)2CuLi a strong base? I thought it was and that if it reacted with a secondary halide it would result in an E2 reaction. But according to the answer key, it seems that a substitution rxn occured instead. Could you please explain why? Thank you

 

[DAT Destroyer]

Question about Organic odyssey chapter 5 #19
Isnt (CH3)2CuLi a strong base? I thought it was and that if it reacted with a secondary halide it would result in an E2 reaction. But according to the answer key, it seems that a substitution rxn occured instead. Could you please explain why? Thank you

No. Not a chance. You are thinking about nucleophiles such as CH3OLi or even CH3MgCl. In the case of (CH3)2CuLi, it is the Gilman Reagent used in a reaction called Corey House in honor of the great Organic Chemist from Harvard EJ Corey. This reagent is NOT a strong base and does NOT do the E2 mechanism. In this reaction, this halogen was SUBSTITUTED for the methyl group. Even to this day, this is one of our most used reagents to alkylate a ring. The nice thing about this alkyl cuprate reagent is that it doesnt interfere with other groups such as aldehydes, alcohols, acids, or ketones.

I hope this helps.

Dr. Romano

 

[Roy Williams]

Bio question 406 in 2015 destroyer asks which organelle is present in both eukaryotes and prokaryotes. The answer was ribosome (which I agree with), but another answer choice is cell wall.

Why couldn't it also be that since plant cells are eukaryotes and have a cell wall, plus some bacteria also have cell walls and they are prokaryotes?

Thanks!

 

[doitfortheppl2016]

No. Not a chance. You are thinking about nucleophiles such as CH3OLi or even CH3MgCl. In the case of (CH3)2CuLi, it is the Gilman Reagent used in a reaction called Corey House in honor of the great Organic Chemist from Harvard EJ Corey. This reagent is NOT a strong base and does NOT do the E2 mechanism. In this reaction, this halogen was SUBSTITUTED for the methyl group. Even to this day, this is one of our most used reagents to alkylate a ring. The nice thing about this alkyl cuprate reagent is that it doesnt interfere with other groups such as aldehydes, alcohols, acids, or ketones.

I hope this helps.

Dr. Romano

Hi Dr. Romano, thank you for the response. I just want to make sure one more time. So, organolithiums and grignard reagents are good nucleophiles and bases but (CH3)2CuLi is just a good nucleophile and not a good base?

 

[DAT Destroyer]

Hi Dr. Romano, thank you for the response. I just want to make sure one more time. So, organolithiums and grignard reagents are good nucleophiles and bases but (CH3)2CuLi is just a good nucleophile and not a good base?

Yes.....pretty much. The alkyl copper reagent is not a base at all, but a nucleophile that does a simple substitution reaction. The exact mechanism is still up for discussion and debate in Advanced Organic chemistry. Alkyl lithium reagents and Grignards are indeed great nucelophiles and powerful bases,they are used most often to attack a carbonyl group to make alcohols. Generally speaking they dont take part in SN2 nor SN1 processes.
You seem to have a good idea. Keep hammering away.

Dr. Romano

 

[doitfortheppl2016]

Thank you Dr. Romano. I have another question regarding friedel craft alkylation on nitrobenzenes. If a nitrobenzene reacted with CH3Cl/FeCl3, would that be no reaction? or would the reaction proceed? I know you answered this question earlier but I didn't quite understand the FeCl3 vs AlCl3 answer. Thank you again

 

[DAT Destroyer]

Thank you Dr. Romano. I have another question regarding friedel craft alkylation on nitrobenzenes. If a nitrobenzene reacted with CH3Cl/FeCl3, would that be no reaction? or would the reaction proceed? I know you answered this question earlier but I didn't quite understand the FeCl3 vs AlCl3 answer. Thank you again

I love your questions !!!!! Yes, it would indeed go with FeCl3. However, FeCl3 is not as powerful of a Lewis base than AlCl3. My experience over the last 30 years always resulted in a better yield with AlCl3.

Hope this helps.

 

[doitfortheppl2016]

I love your questions !!!!! Yes, it would indeed go with FeCl3. However, FeCl3 is not as powerful of a Lewis base than AlCl3. My experience over the last 30 years always resulted in a better yield with AlCl3.

Hope this helps.

Haha thank you again for your response and for helping me. I understand now. But did you mean to say FeCl3 is not as powerful of a lewis acid than AlCl3?

 

[DAT Destroyer]

Haha thank you again for your response and for helping me. I understand now. But did you mean to say FeCl3 is not as powerful of a lewis acid than AlCl3?

Yes, that's correct!🙂

 

[doitfortheppl2016]

I have a question about the DAT Destroyer Ochem #49. In the last step, wouldn't the major product be the E2 product since OTs is on a secondary carbon and since -OCH3 is a strong base? I understand why the SN2 product is produced but in this reaction an E2 product is also formed right? Please correct me if I'm wrong. Thank you again

 

[rak173]

Hello Dr. Romano,

For the 2nd question on bio section about the ebola, that image looks like it's taken from a transmission electron microscope more than the scanning electron microscope. Doesn't the SEM images produce 3d images? That picture doesn't look 3d to me or is it? Thanks.

 

[dentalstudent2021]

one molecule of a compound has a mass of 2 x 10^-22 grams, what is it molecular mass ?

(2 x 10^-22 grams/ molecules ) ( 6x10^23 molecules/mol) = g/mol...

avogadro's number does not have any specific units, correct ? so in this question I don't understand how we say 6x10^23 molecules/mol. how do we determine what the units of avogadro's will be ?

 

[SDDDAT]

one molecule of a compound has a mass of 2 x 10^-22 grams, what is it molecular mass ?

(2 x 10^-22 grams/ molecules ) ( 6x10^23 molecules/mol) = g/mol...

avogadro's number does not have any specific units, correct ? so in this question I don't understand how we say 6x10^23 molecules/mol. how do we determine what the units of avogadro's will be ?

Avogadro's number is basically 6x10^23 of something per mole. You can put whatever you want!

Think of the term "a dozen". Say you have 12 eggs, you could say you have 12 eggs or a dozen eggs. Same thing with Avogadro's number, you could say you have 6x10^23 eggs or you could say you have a mole of eggs.

 

[FutureDent20]

2016 G-chem destroyer #28:
I understand the logic behind this question but I am little confused how 1x10^-12 +1 x 10^-7 is approximately 1x10^-7? and not 1x10^-5?

 

[SDDDAT]

2016 G-chem destroyer #28:
I understand the logic behind this question but I am little confused how 1x10^-12 +1 x 10^-7 is approximately 1x10^-7? and not 1x10^-5?

You're thinking of division of exponents, not addition! I get confused between these two some times too.

When you divide two exponents, you subtract the powers so 1x10^-5 would be the answer if you were asked to divide 1x10^-12 to 1x10^-7.
However, in this case it's asking you to add the two numbers and since 1x10^-12 is so small, your answer is still going to be really close to 1x10^-7.

 

[rak173]

2016 G-chem destroyer #28:
I understand the logic behind this question but I am little confused how 1x10^-12 +1 x 10^-7 is approximately 1x10^-7? and not 1x10^-5?

1 x 10^-12 is 100000 smaller than 1 x 10^-7. Its like adding 1 to 100000 which is 100001 which we can say is same as 100000.

 

[SDDDAT]

I was going over the OC roadmap in destroyer 2014 and noticed that

was called a hemi-acetal.

I thought hemi-acetal has a hydrogen as one of the substituents on the central carbon whereas hemi-ketal has no hydrogen? Are the terms interchangable?

 

[FutureDent20]

You're thinking of division of exponents, not addition! I get confused between these two some times too.

When you divide two exponents, you subtract the powers so 1x10^-5 would be the answer if you were asked to divide 1x10^-12 to 1x10^-7.
However, in this case it's asking you to add the two numbers and since 1x10^-12 is so small, your answer is still going to be really close to 1x10^-7.

1 x 10^-12 is 100000 smaller than 1 x 10^-7. Its like adding 1 to 100000 which is 100001 which we can say is same as 100000.

Uhhhh!!! That makes total sense! feel stupid for asking that question now Thank you guys!

 

[super frank]

I was going over the OC roadmap in destroyer 2014 and noticed that

was called a hemi-acetal.

I thought hemi-acetal has a hydrogen as one of the substituents on the central carbon whereas hemi-ketal has no hydrogen? Are the terms interchangable?

They are not interchangeable. Aldeyhydes -> acetals (thus, a H substituent), ketones -> ketals.

 

[sharkteethdentist]

Dear. Dr. Romano. OC #203 2016 Edition. Why is there conjugation happening to the a, b ketone with organometallic reagent instead of the nucleophilic addition? Are there any differences between CuLi and alkyl lithium as a reagent to form the nucleophilic addition?
Thanks in Advance, Dr. Romano.

 

[DAT Destroyer]

Dear. Dr. Romano. OC #203 2016 Edition. Why is there conjugation happening to the a, b ketone with organometallic reagent instead of the nucleophilic addition? Are there any differences between CuLi and alkyl lithium as a reagent to form the nucleophilic addition?
Thanks in Advance, Dr. Romano.

Great question. The explanation is often argued in many advanced organic texts. I need not bother you with the details, but rather what the experimental results show... If you see a conjugated aldehyde or ketone......add to the carbonyl group if you have a Grignard, Alkyl Lithium reagent, LiAlH4. or NaBH4. If you have a nucleophile like alcohol, thiol, cuprate, amine, etc...add to the beta carbon. It seems that powerful nucleophiles like Grignards prefer the carbonyl addition because charges are involved which dominate orbital factors. With nucleophiles that are weaker, charges are less important and orbital control is the dominating factor.

Hope this helps.

Dr. romano

 

[sharkteethdentist]

Great question. The explanation is often argued in many advanced organic texts. I need not bother you with the details, but rather what the experimental results show... If you see a conjugated aldehyde or ketone......add to the carbonyl group if you have a Grignard, Alkyl Lithium reagent, LiAlH4. or NaBH4. If you have a nucleophile like alcohol, thiol, cuprate, amine, etc...add to the beta carbon. It seems that powerful nucleophiles like Grignards prefer the carbonyl addition because charges are involved which dominate orbital factors. With nucleophiles that are weaker, charges are less important and orbital control is the dominating factor.

Hope this helps.

Dr. romano

Thank you, Dr. Romano

 

[rak173]

Hello Dr. Romano,

For the 2nd question on bio section about the ebola, that image looks like it's taken from a transmission electron microscope more than the scanning electron microscope. Doesn't the SEM microscope produce 3d images? That picture doesn't look 3d to me or is it? Thanks.

 

[doitfortheppl2016]

I have two questions about the 2015 Ochem DAT destroyer section.

1. For problem 60, couldn't ethyl cyclopropane be a constitutional isomer as well?
2. For problem 67, I thought that primary alcohols would undergo SN2 in the presence of a strong acid such as HCl. How come the solution implies that it will undergo Sn1 and do a shift?

Thank you again

 

[salreq]

For 218 in the destroyer, doesn't both choice a and b have the same number of hydrogen bonds?

 

[DAT Destroyer]

I have two questions about the 2015 Ochem DAT destroyer section.

1. For problem 60, couldn't ethyl cyclopropane be a constitutional isomer as well?
2. For problem 67, I thought that primary alcohols would undergo SN2 in the presence of a strong acid such as HCl. How come the solution implies that it will undergo Sn1 and do a shift?

Thank you again

Problem 60 was clarified in the 2016 book. You were to only consider isomers containing a cyclopentane ring. Problem 67.....Usually the primary alcohol does the SN1 process as you so perspicaciously stated......HOWEVER......not if there is branching on the beta carbon........studies have shown that the shift of a methyl group occurs simultaneously with the departure of water to set up a tertiary carbocation. Normally primary alcohols do the SN2 reaction, since the formation of a primary carbocation has an enormous energy barrier. However,,,,once in awhile, we see a primary alcohol with branching on the adjacent carbon do the SN1. If you need further clarity on this, Francis Carey, Paula Bruice and David Klein explain it nicely in their respective texts.

Hope this helps.

Dr. Jim Romano

 

[salreq]

For question 278 from the Organic chemistry destroyer, how are we allowed to just rotate a molecule because Br and H aren't trans to each other? Wouldn't you form choice D by grabbing the hydrogen from the CH3?

Thank you

 

[DAT Destroyer]

For question 278 from the Organic chemistry destroyer, how are we allowed to just rotate a molecule because Br and H aren't trans to each other? Wouldn't you form choice D by grabbing the hydrogen from the CH3?

Thank you

When an E2 reaction occurs, the halogen and hydrogen must be Anti to each other. Get out a model to see this more clearly. In the pictured question, the Bromine and Hydrogen are in the same direction. The molecule needs to be rotated to set up the anti-periplanar relationship. Once in this position, can the orbitals effectively overlap to form the double bond. The Klein text book has nice graphics on this. Choice D would be only a minor product.....maybe 10% or so, since it is the less substituted alkene.

Hope this helps

Dr. Romano

 

[doitfortheppl2016]

Problem 60 was clarified in the 2016 book. You were to only consider isomers containing a cyclopentane ring. Problem 67.....Usually the primary alcohol does the SN1 process as you so perspicaciously stated......HOWEVER......not if there is branching on the beta carbon........studies have shown that the shift of a methyl group occurs simultaneously with the departure of water to set up a tertiary carbocation. Normally primary alcohols do the SN2 reaction, since the formation of a primary carbocation has an enormous energy barrier. However,,,,once in awhile, we see a primary alcohol with branching on the adjacent carbon do the SN1. If you need further clarity on this, Francis Carey, Paula Bruice and David Klein explain it nicely in their respective texts.

Hope this helps.

Dr. Jim Romano

Thank you Dr. Romano. It makes sense now (=

 

[dentalstudent2021]

Benzene does not have true double bonds BUT it does have 6 pi electrons. I don't quite grasp this as I always thought, to have pi bonds you need to have double/triple bonds. is benzene the only special case due to delocalization ? Thanks.

 

[Freakoutfrank]

Hello, Purchased the latest Destroyer version about a month ago. I wanted to know if there is an updated 2016 answer tracker excel sheet available for purchase/download. I know in past years there excel sheets have been made available.

Thanks in advance.