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!

 

[adamrose]

Question 238 Orgo 2012 destroyer
Image 1760: I thought Grignard reagents attack and add to electrophilic carbons? In this example the grignard is functioning as a base and extracting an H which I have never seen before. Should I only worry about grignard functioning as a strong base when I have an acidic hydrogen such as in an acetylide ion?

 

[Jay20155555]

For the DAT destroyer 2015, Gen Chem question 17.

It asks which statements are true about the electrolysis of water.

I understand why A and D are correct but how would you know O2 is created at the anode? I know the anode in an electrolytic cell is positive and the cathode is negative. The reaction is H2O + 2e- --> H2(g) + O2(g). how would you know which is made where since neither have a charge? Are H+ ions attracted to the negative charge on the cathode which makes hydrogen gas, and if so would the O2 gas being made be O- in solution? which then would be attracted to the anode to make Oxygen gas?

 

[DAT Destroyer]

For the DAT destroyer 2015, Gen Chem question 17.

It asks which statements are true about the electrolysis of water.

I understand why A and D are correct but how would you know O2 is created at the anode? I know the anode in an electrolytic cell is positive and the cathode is negative. The reaction is H2O + 2e- --> H2(g) + O2(g). how would you know which is made where since neither have a charge? Are H+ ions attracted to the negative charge on the cathode which makes hydrogen gas, and if so would the O2 gas being made be O- in solution? which then would be attracted to the anode to make Oxygen gas?

You must remember oxidized at the Anode and reduced at the cathode.

Oxygen in water has a -2 charge, but O2 is 0.

So it lost electrons, therefore it oxidized.

Since it was oxidized, it must be in the anode.

Hope this helps.

 

[510586]

Question 238 Orgo 2012 destroyer
Image 1760: I thought Grignard reagents attack and add to electrophilic carbons? In this example the grignard is functioning as a base and extracting an H which I have never seen before. Should I only worry about grignard functioning as a strong base when I have an acidic hydrogen such as in an acetylide ion?

No this is what it does to a carboxylic acid as well (extract an H). Grignards add to electrophilic carbons if there are not acidic hydrogens (e.g CtriplebondCH or OH or NH). I missed a few problems like this but I think I understand it now. Hopefully someone clarifies or provides more examples other than CCH OH and NH.

 

[adamrose]

on what

No this is what it does to a carboxylic acid as well (extract an H). Grignards add to electrophilic carbons if there are not acidic hydrogens (e.g CtriplebondCH or OH or NH). I missed a few problems like this but I think I understand it now. Hopefully someone clarifies or provides more examples other than CCH OH and NH.

On what type of molecule is there just an N-H bond? do you mean any type of amine or amide

 

[510586]

on what

On what type of molecule is there just an N-H bond? do you mean any type of amine or amide

Yea those are considered acidic. BUT I am not sure about amide. Odessy says amides are neutral, but maybe the NH is still acidic? I hope Dr. Romano comes and answers this so I don't have to make a whole thread about it

 

[510586]

I'm seeing a lot of questions that state that progesterone inhibit FSH release or LH (which is correct because hypothalamus senses more of it so doesn't produce GnRH for the anterior pituitary so less FSH and LH). Would estrogen do this as well? Like inhiibit FSH or LH

 

[DAT Destroyer]

Question 238 Orgo 2012 destroyer
Image 1760: I thought Grignard reagents attack and add to electrophilic carbons? In this example the grignard is functioning as a base and extracting an H which I have never seen before. Should I only worry about grignard functioning as a strong base when I have an acidic hydrogen such as in an acetylide ion?

This is a VERY important problem. The Grignard can act as a base towards an alkyne.....since the hydrogen is quite easy to abstract. Once removed.....we have created an acetylenic Grignard......which can now attack a carbonyl. This is a very common reaction. If you need more practice, consult a text such as Wade, Klein , or McMurray.

Hope this helps.

Dr. Romano

 

[adamrose]

This is a VERY important problem. The Grignard can act as a base towards an alkyne.....since the hydrogen is quite easy to abstract. Once removed.....we have created an acetylenic Grignard......which can now attack a carbonyl. This is a very common reaction. If you need more practice, consult a text such as Wade, Klein , or McMurray.

Hope this helps.

Dr. Romano

What are common species with acidic hydrogens besides Terminal acetylides carbox acids and NH compounds? I am not clear what exactly makes an H acidic

 

[adamrose]

I'm seeing a lot of questions that state that progesterone inhibit FSH release or LH (which is correct because hypothalamus senses more of it so doesn't produce GnRH for the anterior pituitary so less FSH and LH). Would estrogen do this as well? Like inhiibit FSH or LH

I think I remember from my physiology class that in the first half of the ovarian cycle, estrogen has an inhibiting effect, but midway through it has a stimulating effect. inhibiting/stimulating on what though? I have no idea

 

[DAT Destroyer]

What are common species with acidic hydrogens besides Terminal acetylides carbox acids and NH compounds? I am not clear what exactly makes an H acidic

Be Careful here ! We used a Grignard on an alkyne to create a new Grignard,,,,,,,However, acidic protons normally destroy the Grignard. H20, alcohols, carboxy acids, thiols, even amines are acidic enough to destroy the Grignard.

Hope this helps.

Dr. Romano

 

[510586]

I think I remember from my physiology class that in the first half of the ovarian cycle, estrogen has an inhibiting effect, but midway through it has a stimulating effect. inhibiting/stimulating on what though? I have no idea

Well all I know is the hypothalamus releases GnRH when estrogen and progesterone are low, so I just applied that logic to the reason progesterone would lower LH and FSH. Hopefully someone answers

 

[510586]

Can someone explain why B is wrong? The answer given in the back of the book says none of these but the provided answer looks like b..

 

[DAT Destroyer]

Can someone explain why B is wrong? The answer given in the back of the book says none of these but the provided answer looks like b..

B is correct and the solution is correct, sorry a typo in letter choice that will be corrected...

This is simply forming an enamine, then hydrolyzing the product to form the desired carbonyl compound.

I have done this reaction for many years, the yields are FANTASTIC !!!!!

Dr. Romano

 

[510586]

B is correct and the solution is correct, sorry a typo in letter choice that will be corrected...

This is simply forming an enamine, then hydrolyzing the product to form the desired carbonyl compound.

I have done this reaction for many years, the yields are FANTASTIC !!!!!

Dr. Romano

Awesome thanks Dr Romano!

 

[510586]

B is correct and the solution is correct, sorry a typo in letter choice that will be corrected...

This is simply forming an enamine, then hydrolyzing the product to form the desired carbonyl compound.

I have done this reaction for many years, the yields are FANTASTIC !!!!!

Dr. Romano

Dr. Romano can you explain this question?http://forums.studentdoctor.net/thr...thode-the-fastest-in-electrophoresis.1148365/

 

[Tooth.be.told]

Smart humans:
In question #62, biology section. IT says that Sarcoma occurs only in connective tissue. However as I google different sites, it says that they are malignant tumors of connective tissue or other non-epithelial tissues.
Can someone clarify that for me please

 

[ThunderSplash]

On the 2015 destroyer, gen chem number 79. I just don't get voltaic cells. Memorized them enough to regurgitate and that was about it. Reading about it online doesn't help. Anyone care to reword the solution to 79 in order to try and make it make sense for me? Thank you!!

 

[510586]

On the 2015 destroyer, gen chem number 79. I just don't get voltaic cells. Memorized them enough to regurgitate and that was about it. Reading about it online doesn't help. Anyone care to reword the solution to 79 in order to try and make it make sense for me? Thank you!!

First understand that you don't multiply Eo by anything (even if it's like 2 Fe and 3 Co in the balanced equation. Then understand that voltaic cells and galvanic cells are spontaneous (-deltaG and + E) while electrolytic cells are nonspontaneous (take energy) to produce elements in general. In both of them, the electrons travel from anode to cathode. So if you see a galvanic/voltaic cell, you need the Eo to add up to be a positive number. Something is always reduced while something else is oxidized in these questions. You want it to be spontaneous, so in question 79 we would want Fe+3 to be reduced because +.75 would result in a + Eo regardless of the -.3. Because Fe+3 is being reduced, that means Co is being oxidized so switch the sign of it to be Co -> Co2+ + 2e- and switch the sign of its Eo to reflect that -.3 to +.3. Then add them together (without multiplying them by anything) to make .3+.75 = +1.05. Let me know if anything needs to be cleared up and hopefully I can get it

 

[DAT Destroyer]

On the 2015 destroyer, gen chem number 79. I just don't get voltaic cells. Memorized them enough to regurgitate and that was about it. Reading about it online doesn't help. Anyone care to reword the solution to 79 in order to try and make it make sense for me? Thank you!!

This is a VERY VERY important problem.

A voltaic cell is a spontaneous device, meaning that it is driven by a redox reaction. The Cell Potential MUST be positive. This eliminates any negative choices. Now look at the two half cell reactions. Both are written in terms of reductions, correct ?

In a redox process, one reaction is reduction and the other MUST be an oxidation. Since the cell potential MUST be positive,,,,,,keep the reaction that is more positive....and REVERSE the less positive half reaction.

Doing this gives one reduction and one oxidation process. Thus we get .75 + .30 to yield 1.05 volts.

I hope this helps.

Dr Romano

 

[adamrose]

#61 Orgo 2012

Tert-butyl Iodide with added reagent CH3OH(aq)
Apparently this forms an ester and not an alkene? (the question asks which reaction could form an alkene and I chose this one)

According to these rules shouldn't it form an alkene?

"If tertiary alkyl halide:
Determine if base is strong
If it is, E2
If it isn't, SN1 and E1

Tertiary alkyl halide. Check
Weak Base, Check.
Why not alkene?

 

[510586]

#61 Orgo 2012

Tert-butyl Iodide with added reagent NaOCH3 in CH3OH solvent
Apparently this forms an ester and not an alkene? (the question asks which reaction could form an alkene and I chose this one)

According to these rules shouldn't it form an alkene?

"If tertiary alkyl halide:
Determine if base is strong
If it is, E2
If it isn't, SN1 and E1

Tertiary alkyl halide. Check
Weak Base, Check.
Why not alkene?

That is odd. In 2015 destroyer there was a statement saying that strong bases such as Ch3O-Na+ favor E2 reactions when reacted with 3 degree halides, which seems to be exactly that question. Numbber 124 of 2015 OC

 

[adamrose]

That is odd. In 2015 destroyer there was a statement saying that strong bases such as Ch3O-Na+ favor E2 reactions when reacted with 3 degree halides, which seems to be exactly that question. Numbber 124 of 2015 OC

**** i made a typo. does it make sense what Im asking now?

 

[510586]

**** i made a typo. does it make sense what Im asking now?

No problem. Base is weak so it does SN1 or e1 because their carbocations are stable b/c tertiary. Was there a better answer choice? Also do you mean ether not ester?

 

[bodmon]

from 2013 Q152:
Consider the following elementary steps which would be least likely to occur?

a) X + Y --> Z
b) 2X + Y --> Z
c) 2X + 2Y --> W+Z
d) 2X --> X + Y
e) 2X + Y --> 2W + Z

Answer: c) a reaction will occur when there is a collision, more reactants involved the less likely for a fruitful collision since in C) there are 4 reactants, it is not likely to occur

When i approached this question I thought of entropy, which lead me to the answer of B) since I thought there were 3 reactants with one product (more orderly) so it would have been less likely. Do you only think about entropy and compare the number of reactants with products when its specifically stated that it is a gas?

 

[510586]

#61 Orgo 2012

Tert-butyl Iodide with added reagent CH3OH(aq)
Apparently this forms an ester and not an alkene? (the question asks which reaction could form an alkene and I chose this one)

According to these rules shouldn't it form an alkene?

"If tertiary alkyl halide:
Determine if base is strong
If it is, E2
If it isn't, SN1 and E1

Tertiary alkyl halide. Check
Weak Base, Check.
Why not alkene?

Hey did you ever find out about this

 

[Lnguyen7]

#61 Orgo 2012

Tert-butyl Iodide with added reagent CH3OH(aq)
Apparently this forms an ester and not an alkene? (the question asks which reaction could form an alkene and I chose this one)

According to these rules shouldn't it form an alkene?

"If tertiary alkyl halide:
Determine if base is strong
If it is, E2
If it isn't, SN1 and E1

Tertiary alkyl halide. Check
Weak Base, Check.
Why not alkene?

Tert-butyl Iodide is tertiary and CH3OH is a weak nucleophile. These conditions favor SN1, thus you make an ether (CH3)3-OCH3 and not an alkene.

 

[510586]

Tert-butyl Iodide is tertiary and CH3OH is a weak nucleophile. These conditions favor SN1, thus you make an ether (CH3)3-OCH3 and not an alkene.

Why do they not favor e1? Sn1 usually make e1 products as well

 

[Lnguyen7]

Why do they not favor e1? Sn1 usually make e1 products as well

Yes, E1 products are also formed. High temperature favors E1.

 

[DAT Destroyer]

from 2013 Q152:
Consider the following elementary steps which would be least likely to occur?

a) X + Y --> Z
b) 2X + Y --> Z
c) 2X + 2Y --> W+Z
d) 2X --> X + Y
e) 2X + Y --> 2W + Z

Answer: c) a reaction will occur when there is a collision, more reactants involved the less likely for a fruitful collision since in C) there are 4 reactants, it is not likely to occur

When i approached this question I thought of entropy, which lead me to the answer of B) since I thought there were 3 reactants with one product (more orderly) so it would have been less likely. Do you only think about entropy and compare the number of reactants with products when its specifically stated that it is a gas?

You seem to be confusing an elementary step.....which is part of a mechanism to a complete reaction. It is true that an increase of gaseous products would be indicative of being entropy driven. In this problem, we are given ELEMENTARY steps. A bimolecular reaction is most common. The chances of 4 particles colliding in proper spatial alignment is highly improbable.

Hope this helps.

Dr. Romano

 

[510586]

Yes, E1 products are also formed. High temperature favors E1.

He said it didn't form an alkene. Dr Romano do you know what is going on? I don't have his version of destroy

 

[bodmon]

You seem to be confusing an elementary step.....which is part of a mechanism to a complete reaction. It is true that an increase of gaseous products would be indicative of being entropy driven. In this problem, we are given ELEMENTARY steps. A bimolecular reaction is most common. The chances of 4 particles colliding in proper spatial alignment is highly improbable.

Hope this helps.

Dr. Romano

Thank you for clearing that up! I guess it was a reading mistake of not recognizing that it was the elementary steps

 

[510586]

From preproinsulin and pro-insulin These precursor molecules undergo hydrolysis reactions that modify them into the active insulin. Specific protease enzymes cleave 2 peptide bonds that allow the mature insulin to form. Where does this take place?

 

[DCG anonymous]

GenChem 2015 #89. Why must we convert to grams I thought this equation used mass?

 

[DCG anonymous]

GenChem 2015 #89. Why must we convert to grams I thought this equation used mass?

Sorry I meant to moles

 

[DAT Destroyer]

Sorry I meant to moles

Look closely at the heat of vaporization . Take note that the value is expressed in KJ/mole, therefore express mass in moles.

Hope this helps

Dr. Romano

 

[DCG anonymous]

For Gen chem #158 what is the reasoning as to why E is + for the oxidation of Cr to Cr3+?

 

[DAT Destroyer]

For Gen chem #158 what is the reasoning as to why E is + for the oxidation of Cr to Cr3+?

Hello Predentjim

The reverse of any half reaction is the opposite sign !!!!!!

Notice the overall reaction has Cr on the left and Cr+3 on the right......the data has Cr+3 on LEFT and Cr on the right.....thus the sign must be switched.

This is a HUGE problem.

Also note that coefficients are not included when doing cell potentials.

Why ?

Cell potential is an INTENSIVE PROPERTY and is independent of amount of substance.. If you are still having trouble, please consult one of the General Chem texts. My favorites are Chang and Ebbing.

Hope this helps.

Dr. Romano

 

[DCG anonymous]

Hello Predentjim

The reverse of any half reaction is the opposite sign !!!!!!

Notice the overall reaction has Cr on the left and Cr+3 on the right......the data has Cr+3 on LEFT and Cr on the right.....thus the sign must be switched.

This is a HUGE problem.

Also note that coefficients are not included when doing cell potentials.

Why ?

Cell potential is an INTENSIVE PROPERTY and is independent of amount of substance.. If you are still having trouble, please consult one of the General Chem texts. My favorites are Chang and Ebbing.

Hope this helps.

Dr. Romano

Thanks again!

 

[DCG anonymous]

Has anyone figured out ochem 2015 #284?
Carbon 2 is driving me nuts as to how they got R. I thought the carboxy C would get priority over C-3 since C2 is attached to (O,O,O).

Thanks!

 

[ThunderSplash]

Has anyone figured out ochem 2015 #284?
Carbon 2 is driving me nuts as to how they got R. I thought the carboxy C would get priority over C-3 since C2 is attached to (O,O,O).

Thanks!

Almost. Going down through carbon 3 has a C bonded to a Cl, which makes it automatically a higher priority than the carbonyl. Does that make sense?

 

[DCG anonymous]

Almost. Going down through carbon 3 has a C bonded to a Cl, which makes it automatically a higher priority than the carbonyl. Does that make sense?

Yes thanks. I was trying to compare all of the three atoms on the next bonds over from the carbons which was giving me the opposite of that

 

[ThunderSplash]

Yes thanks. I was trying to compare all of the three atoms on the next bonds over from the carbons which was giving me the opposite of that

Just in case it confuses others, I tried my best to show it visually.

 

[hockeyboyrw]

Hi Dr. Romano

I was going through Organic Chemistry Odyssey 2015 and came across question 41 where it asks which is fastest, reaction 1: SH- with 2-iodobutane in DMF with a substitution or reaction 2: with OH- reacting with 2-iodobutane in DMF with the same substitution. The answer provided is B reaction 1 since SH- is a stronger nucleophile than OH- and I checked the thread about with DAT Destroyer questions on SDN and found you replied that sulfur and phosphorus are less electronegative than oxygen and nitrogen respectively thus even in a aprotic solvent like DMF they still react faster.

So for the DAT should I just ignore the trends in nucleophilicity in protic vs aprotic solvents and just determine it solely based on less electronegative atoms are better nucleophiles because that's what it seems like in your response on this linkhttp://forums.studentdoctor.net/threads/official-dat-destroyer-q-a-thread.1121970/page-8 . If I shouldn't ignore the trends when should I apply them and when shouldn't I. Sorry if I'm coming off as nit-picky but, I'm just lost at this point now. Thank you!

 

[DAT Destroyer]

Hi Dr. Romano

I was going through Organic Chemistry Odyssey 2015 and came across question 41 where it asks which is fastest, reaction 1: SH- with 2-iodobutane in DMF with a substitution or reaction 2: with OH- reacting with 2-iodobutane in DMF with the same substitution. The answer provided is B reaction 1 since SH- is a stronger nucleophile than OH- and I checked the thread about with DAT Destroyer questions on SDN and found you replied that sulfur and phosphorus are less electronegative than oxygen and nitrogen respectively thus even in a aprotic solvent like DMF they still react faster.

So for the DAT should I just ignore the trends in nucleophilicity in protic vs aprotic solvents and just determine it solely based on less electronegative atoms are better nucleophiles because that's what it seems like in your response on this linkhttp://forums.studentdoctor.net/threads/official-dat-destroyer-q-a-thread.1121970/page-8 . If I shouldn't ignore the trends when should I apply them and when shouldn't I. Sorry if I'm coming off as nit-picky but, I'm just lost at this point now. Thank you!

Let us review a few things..... In a polar aprotic solvent such as Diethyl ether, DMSO, DMF.....we favor the SN2 process. SN2 reactions are favored by strong nucleophiles like Sulfur and CN-. The nucleophile is not captured by the solvent. For halogen nucleophiles... the trend is as follows : F->Cl->Br->I- in polar aprotic solvents. It turns out for reasons not completely understood a Sulfur , Phosphorus or CYANIDE CN-, nucleophile works great in BOTH polar and aprotic solvents.

My theory is that these atoms are very big ( at least as far as S and P are concerned ) and posses loosely bound electrons......therefore the solvent does little to inhibit their nucleophilicity. A polar protic solvent such as water or alcohol usually accelerates an SN1 reaction by stabilizing the incipient carbocation, thus lowering the Potential Energy of the transition state. Hence, Fluoride nucleophile is DEAD!!!! The order now becomes I- >Br->Cl->>> F-. The nucleophile is literally captured by the solvent !!!!

If you follow all this.....the DAT will be a piece of cake. Just remember,,,,,when using CN-...this nucleophile LOVES to do SN2, regardless of the solvent. I have been studying solvents for over 30 years,,,,,,and many unexpected outcomes do result.

I have spoken to world class Chemists such as Skip Wade , Mike Smith, and Maitland Jones of Princeton...... and they are even baffled at times !!!!

Feel free to post questions from this point out on this topic, and I will be sure to answer them as soon as I get out of lectures. .

I hope this helps.

Dr. Jim Romano

 

[510586]

http://forums.studentdoctor.net/thr...ion-naming-vinylic-vs-allylic-groups.1151222/ I apologize for double posting, but can someone clear up this confusion on naming allyls vs vinyls please?

 

[DAT Destroyer]

http://forums.studentdoctor.net/thr...ion-naming-vinylic-vs-allylic-groups.1151222/ I apologize for double posting, but can someone clear up this confusion on naming allyls vs vinyls please?

A vinyl group is the 2 carbon group.....the allyl is the 3 carbon group.
-CH2-CH=CH2 is the allyl group
CH=CH2 is vinyl group

Hope this helps

Dr. Romano

 

[510586]

A vinyl group is the 2 carbon group.....the allyl is the 3 carbon group.
-CH2-CH=CH2 is the allyl group
CH=CH2 is vinyl group

Hope this helps

Dr. Romano

How come when it was coming off the parent chain in the second picture we name it allyl? Aren't there only 2 carbons coming off?

 

[DAT Destroyer]

How come when it was coming off the parent chain in the second picture we name it allyl? Aren't there only 2 carbons coming off?

The first compound is 4-methyl-3-vinylcyclohexanone. The second compound you posted is called 3-allyl-2-methylcyclohexanone. Please review the functional groups.

Hope this helps.

Dr. Romano

 

[hockeyboyrw]

It turns out for reasons not completely understood a Sulfur , Phosphorus or CYANIDE CN-, nucleophile works great in BOTH polar and aprotic solvents.

If you follow all this.....the DAT will be a piece of cake. Just remember,,,,,when using CN-...this nucleophile LOVES to do SN2, regardless of the solvent. I have been studying solvents for over 30 years,,,,,,and many unexpected outcomes do result.

So essentially the trends in nucleophilicity in polar protic vs aprotic solvents, (increase in nucleophilicity going down a group and to the left in period in polar protic; while increase in nucleophilicity going up a group in aprotic and increase going left in a period in aprotic), will be followed on the DAT, except when using CN-, Sulfur, or Phosphorus. These 3 are the exceptions and will be more nucleophilic in aprotic solvents still even if the other nucleophile(s) we compare it to is/are smaller.