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!

 

[FutureDent20]

Question 172 2016 G-chem:
Lets say instead of finding the concentration of HBr, we had to find the concentration of H2SO4. My question is, since both H's dissociate completely in H2SO4, do we have to multiply the final answer by 2? as follow:
(0.024) x (20ml) = ( M2) x (48ml)
M2 = 0.01M x (2) = 0.02M of H2SO4

 

[dentalstudent2021]

So H2SO4 is an interesting one as only 1 H in it dissociates. I remember this from chads video.

 

[FutureDent20]

So H2SO4 is an interesting one as only 1 H in it dissociates. I remember this from chads video.

Yeah, That's what I thought. To be more specific 1 H completely dissociates and other half dissociates. But destroyer mentions both dissociates completely. That's where my mind started drifting away

 

[DAT Destroyer]

Question 172 2016 G-chem:
Lets say instead of finding the concentration of HBr, we had to find the concentration of H2SO4. My question is, since both H's dissociate completely in H2SO4, do we have to multiply the final answer by 2? as follow:
(0.024) x (20ml) = ( M2) x (48ml)
M2 = 0.01M x (2) = 0.02M of H2SO4

Lets say we found N = 0.2 for H2S04,,,,,,,Since Normality is always GREATER than or equal to Molarity......
we would DIVIDE by 2 to achieve the answer of 0.1 M.

Hope this helps.

Dr. Romano

 

[FutureDent20]

Lets say we found N = 0.2 for H2S04,,,,,,,Since Normality is always GREATER than or equal to Molarity......
we would DIVIDE by 2 to achieve the answer of 0.1 M.

Hope this helps.

Dr. Romano

That you Dr. Romano! That makes perfect sense.

 

[klownzo]

Question 319 2016 gen chem

I remember reading in orgo as a second language that you want to avoid giving an element a +2/-2 charge when looking at resonance structures. I don't have the book with me to double check but just looking for some insight on this. Thanks!

 

[predentalstudent9]

Question 118 of Gen Chem section in DAT Destroyer 2014: Which statements are false? The answer is "magnesium has third ionization energy slightly higher than its second ionization energy."

Why is this statement false? I thought Mg does have a larger ionization energy compared to its second one since Mg has 2 valence electrons?

 

[DAT Destroyer]

Question 319 2016 gen chem

I remember reading in orgo as a second language that you want to avoid giving an element a +2/-2 charge when looking at resonance structures. I don't have the book with me to double check but just looking for some insight on this. Thanks!

You are correct. The structure with an atom having lots of formal charge is less stable.
However, the questions is asking "How many resonance forms can be drawn?", not "Which resonance form is more stable?".

That is why answer is C, 3 forms.

Hope this helps.

 

[TheSandlapper]

I was thinking about purchasing Destroyer but before I pulled the trigger I wanted a slightly better idea what I'm buying. Is this just a lot of practice problems? Is there any explanation provided with the answers, or just a letter for the correct choice? Also, about how many questions are their per section?

 

[DAT Destroyer]

I was thinking about purchasing Destroyer but before I pulled the trigger I wanted a slightly better idea what I'm buying. Is this just a lot of practice problems? Is there any explanation provided with the answers, or just a letter for the correct choice? Also, about how many questions are their per section?

2016 DAT Destroyer, each problem contains very detailed solutions
Orgo 321
bio 592
gen chem 357
math 153

Plus Orgo Roadmaps and 25 most asked Organic Chemistry Reactions

Nancy

 

[klownzo]

You are correct. The structure with an atom having lots of formal charge is less stable.
However, the questions is asking "How many resonance forms can be drawn?", not "Which resonance form is more stable?".

That is why answer is C, 3 forms.

Hope this helps.

Makes sense! I guess I took it as they simply don't form because they're too unstable. Thanks for the insight!

 

[rak173]

I was thinking about purchasing Destroyer but before I pulled the trigger I wanted a slightly better idea what I'm buying. Is this just a lot of practice problems? Is there any explanation provided with the answers, or just a letter for the correct choice? Also, about how many questions are their per section?

I highly recommend it.

 

[FutureDent20]

Question 118 of Gen Chem section in DAT Destroyer 2014: Which statements are false? The answer is "magnesium has third ionization energy slightly higher than its second ionization energy."

Why is this statement false? I thought Mg does have a larger ionization energy compared to its second one since Mg has 2 valence electrons?

write down the electron configuration for Mg, you see that it has 2 valence (outer) electrons. First ionization energy removes one of those valence electrons, second ionization energy removes the second valence electrons. now with third ionization energy it take way way more energy to remove the third electron because you are now removing the "core" electrons. So, the word "slightly" is wrong.

 

[FutureDent20]

Organic Odyssey Chapter 8: Question #33:

When we do E2, the hydrogen that we are removing and LG have to be anti-coplanar to each other and also it follows Zaitsev's rule. Now, in this case since no stereochemistry is shown how do we know which B-carbon on the ring is going to lose the hydrogen (meaning which hydrogen is anti-complanar to LG)? Or do we just ignore it and follow Zaitsev's rule since stereochemistry is not shown? Because I thought this is one of the exceptions where we remove H from least substituted B-carbon.

 

[rak173]

Hello Dr. Romano,

I have question about Gen Chem # 206 it says that a catalyst would change the specific rate constant. I thought rate constants were affected only by temperature and nothing else. So do catalysts affect rate constants too?

Thanks.

 

[DAT Destroyer]

Hello Dr. Romano,

I have question about Gen Chem # 206 it says that a catalyst would change the specific rate constant. I thought rate constants were affected only by temperature and nothing else. So do catalysts affect rate constants too?Thanks.

An EQUILIBRIUM constant will change with temperature......but a rate constant changes by many other parameters such as Steric effects, solvents, pressure, temperature, catalysts, etc. A catalyst will usually INCREASE a rate constant. I hope this helps.

 

[DAT Destroyer]

Organic Odyssey Chapter 8: Question #33:

When we do E2, the hydrogen that we are removing and LG have to be anti-coplanar to each other and also it follows Zaitsev's rule. Now, in this case since no stereochemistry is shown how do we know which B-carbon on the ring is going to lose the hydrogen (meaning which hydrogen is anti-complanar to LG)? Or do we just ignore it and follow Zaitsev's rule since stereochemistry is not shown? Because I thought this is one of the exceptions where we remove H from least substituted B-carbon.

Good call. If no stereochemistry is implied always show the more stable ZAITZEV product.

 

[farzi2492]

Math Destroyer Test 1 Q 6: how does 21/ (x-2) + 21/(x+2) = 10 reduce to 5x^2-21x-20?

 

[DAT Destroyer]

Math Destroyer Test 1 Q 6: how does 21/ (x-2) + 21/(x+2) = 10 reduce to 5x^2-21x-20?

 

[FutureDent20]

2016 GC destroyer question #344:
I get this question, but how come it states that cobalt (Co) have 2 valence electrons? I thought 3d sub shell counts towards valence electrons when it's not full. So, shouldn't Co have total of 9 valence electrons instead?
or is it only when we are calculating the effective nuclear charge we say it has two valence electrons since they are the most outer shell electrons?

 

[farzi2492]

View attachment 202461

THANK YOU SO MUCH!! definitely makes sense now!

 

[gangazi]

2016 DAT Destroyer
*General Chemistry Section Q#119 -- Combustion of C2H4 gas under 1atm, 25 degrees celcius

My question: When does the combustion reaction produce LIQUID OR GAS water? I used Hf of H2O(g) because when I see something burn, I never see liquid water so I thought the combustion produces H2O vapor... Can you clarify on when the combustion produces liquid water and when it produces gas water?

Thank you so much!

 

[FutureDent20]

For the effective Nuclear charge, you count only the outermost electrons, that is the electrons that are farthest from the nucleus and cannot feel the full effect of the nuclear charge.

Hope this helps.

Thank you Dr. Romano. Like always your explanations makes perfect sense. Just to clarify, aside from this question, Co does have 9 valence electrons right?

 

[FutureDent20]

2016 DAT Destroyer
*General Chemistry Section Q#119 -- Combustion of C2H4 gas under 1atm, 25 degrees celcius

My question: When does the combustion reaction produce LIQUID OR GAS water? I used Hf of H2O(g) because when I see something burn, I never see liquid water so I thought the combustion produces H2O vapor... Can you clarify on when the combustion produces liquid water and when it produces gas water?

Thank you so much!

I believe, it has something to do with conditions such as temperature. Combustion produces a lot of heat and as a result water vapor is produces along with CO2 gas. But the water vapor quickly condenses to liquid water as it cools to the ambient temperature, assuming the ambient temperature is below 100C. That's my take away. Someone, please correct me if I am wrong.

 

[dentalstudent2021]

Hello, does the nitration of aniline give para product due to sterics ? curious as to why not ortho ? since NH2 is O/P directing. Thanks.

 

[FutureDent20]

Hello, does the nitration of aniline give para product due to sterics ? curious as to why not ortho ? since NH2 is O/P directing. Thanks.

So it turns out to do direct nitration on aniline the amino group needs to be protected thought acetylation. Now we can do nitration, and since acetyl protecting group is a bulky group it preferentially direct the nitration to the para position rather than the ortho position.

 

[DAT Destroyer]

Thank you Dr. Romano. Like always your explanations makes perfect sense. Just to clarify, aside from this question, Co does have 9 valence electrons right?

2016 DAT Destroyer
*General Chemistry Section Q#119 -- Combustion of C2H4 gas under 1atm, 25 degrees celcius

My question: When does the combustion reaction produce LIQUID OR GAS water? I used Hf of H2O(g) because when I see something burn, I never see liquid water so I thought the combustion produces H2O vapor... Can you clarify on when the combustion produces liquid water and when it produces gas water?

Thank you so much!

The phase of water is determined by the temperature at which the reaction occurs. Most reactions occur at room temperature, , at which water is a liquid. If the temperature is greater than the boiling point, then the water will be a gas. Since the reaction began at 25 C....use liquid water.

Hope this helps.

Dr. Romano

 

[DAT Destroyer]

2016 GC destroyer question #344:
I get this question, but how come it states that cobalt (Co) have 2 valence electrons? I thought 3d sub shell counts towards valence electrons when it's not full. So, shouldn't Co have total of 9 valence electrons instead?

or is it only when we are calculating the effective nuclear charge we say it has two valence electrons since they are the most outer shell electrons?

Be careful. Here is the confusion....and I feel your pain !!! the Organic Chemists and the General Chemists argue over this fine point and results in mass confusion. The 4s sublevel is regarded as the VALENCE shell in General Chemistry. This works nicely when doing calculations for molecular geometries and effective nuclear charge. On the DAT.....if asked how many valence electrons Co has.....go with 2. However, in Organic Chemistry, we normally use an approximation and count the 3s, 3p, 3d AND the 4s all together when we do transition metal mechanistic work. Bottom line.....When In Gen Chem land ...do as they do.....Cobalt has 2 valence electrons.

I hope this helps.

Dr. Romano

 

[DAT Destroyer]

Hello, does the nitration of aniline give para product due to sterics ? curious as to why not ortho ? since NH2 is O/P directing. Thanks.

Let us talk about the Nitration of Aniline. Ask 5 organic chemists, and you may 5 get different answers. First,,,,from my own experience,,,,,we destroy the compound and get a charry mix of gunk !!!! Some authors such as Mark Loudon, PhD of Purdue and Mait Jones PhD Professor Emeritus of Princeton gives the meta isomer as the major product. Why ? the aniline protonates to give the NH3+ group sitting on top of our ring now,,,,,protonated aniline is now a Meta director !!! This molecule will also be highly deactivated. If asked on the DAT exam, go with the meta product. However, in the Real World...Good luck. It will likely burn and char . We normally would protect the NH2 group with acetyl chloride CH3COCl to do synthetic applications.

I hope this helps on a very interesting question.

I award you with a Gold medal for a great question !!!

Dr. Romano

 

[pearlywhites55]

Hello, does the nitration of aniline give para product due to sterics ? curious as to why not ortho ? since NH2 is O/P directing. Thanks.

Just finished Ochem, and we had to explain this concept on the final exam. I attached an image from our slides that really helped me to understand - sometimes a good visual helps!

All the best!

 

[DAT Destroyer]

Just finished Ochem, and we had to explain this concept on the final exam. I attached an image from our slides that really helped me to understand - sometimes a good visual helps!

All the best!

View attachment 202571

🙂

 

[dentalstudent2021]

why doesn't the base deprotonate the H's on either carbons marked X....why the methyl H's ?

 

[gangazi]

View attachment 202668
why doesn't the base deprotonate the H's on either carbons marked X....why the methyl H's ?

steric hindrance... base is too fat to deprototate H's on X carbons

but I was wondering if they ask for the products, do we ALWAYS ONLY expect anti-zaitsev products? because on Chad teaches that it might go both ways, but destroyer seems to only expect anti-zaitsev

 

[dentalstudent2021]

steric hindrance... base is too fat to deprototate H's on X carbons

but I was wondering if they ask for the products, do we ALWAYS ONLY expect anti-zaitsev products? because on Chad teaches that it might go both ways, but destroyer seems to only expect anti-zaitsev

thanks!! I kept thinking methyl was more bulky for some reason...I think on the DAT, they will only show the most obvious answer which is the hoffman product here...Thanks again.

 

[DAT Destroyer]

View attachment 202668

why doesn't the base deprotonate the H's on either carbons marked X....why the methyl H's ?

The base is very hindered sterically, and will remove the EASIEST most accessible hydrogen, namely those attached to the methyl group. This is critical to know for the DAT exam . As we increase the size of the base, we get more of this elimination. We call this Hofmann Elimination or Anti-Zaitsev.

Hope this helps

Dr. Romano

 

[gangazi]

going over the DAT destroyer's orgo section, I realize the term "unsaturated" used multiple times to describe some of the cyclocompounds... (like pyrrole in #132)
Is there such thung as "fully saturated" cyclocompound? Even cycloalkane has the degree of unsaturation so I was just wondering...
Thank you!

 

[DAT Destroyer]

going over the DAT destroyer's orgo section, I realize the term "unsaturated" used multiple times to describe some of the cyclocompounds... (like pyrrole in #132)
Is there such thung as "fully saturated" cyclocompound? Even cycloalkane has the degree of unsaturation so I was just wondering...
Thank you!

When the term saturated is used in Organic Chemistry, it means that only single bonds are between Carbon atoms. Alkanes and cycloalkanes are examples. An unsaturated compound means there are double or triple bonds between carbons.

Hope this helps

Dr. Romano

 

[dentalstudent2021]

so, on this one. why don't we get the product marked X ?
thought since tBuOk is bulkly base I would think it would abstract the least hindered H. does it do H rearrangement ?

 

[gangazi]

When the term saturated is used in Organic Chemistry, it means that only single bonds are between Carbon atoms. Alkanes and cycloalkanes are examples. An unsaturated compound means there are double or triple bonds between carbons.

Hope this helps

Dr. Romano

Thank you Dr. Romano! so saturated cycloalkane can exist, but it will have a degree of unsaturation. Correct? Thank you as always!

 

[gangazi]

so, on this one. why don't we get the product marked X ?
thought since tBuOk is bulkly base I would think it would abstract the least hindered H. does it do H rearrangement ?

Thats a good question... I would like to know answer to this as well!

 

[DAT Destroyer]

Thank you Dr. Romano! so saturated cycloalkane can exist, but it will have a degree of unsaturation. Correct? Thank you as always!

Yes this is correct, it can indeed be confusing for the beginning student. Let's do an example, cyclohexane is a saturated molecule but has 1 degree of unsaturation.

 

[DAT Destroyer]

so, on this one. why don't we get the product marked X ?
thought since tBuOk is bulkly base I would think it would abstract the least hindered H. does it do H rearrangement ?

This is an example of a secondary halide that is being reacted with a strong big bulky base. The major product formed will be the Hofmann Product which is product X. The use of a strong base such as this will give the less substituted alkene, which is choice X. This is an important question for the DAT. You should review elimination reactions from a text written by a PhD chemist, I recommend the David Klein or Frances Carey text for clarification.

Dr. Romano

 

[dentalstudent2021]

This is an example of a secondary halide that is being reacted with a strong big bulky base. The major product formed will be the Hofmann Product which is product X. The use of a strong base such as this will give the less substituted alkene, which is choice X. This is an important question for the DAT. You should review elimination reactions from a text written by a PhD chemist, I recommend the David Klein or Frances Carey text for clarification.

Dr. Romano

Thanks you Dr. Romano. Does it make a difference if the base was instead C2H5O-K+ ? This was a part of Question 109 in 2015 destroyer, and "X" was not considered the product with the base C2H5O-K+.

 

[DAT Destroyer]

Thanks you Dr. Romano. Does it make a difference if the base was instead C2H5O-K+ ? This was a part of Question 109 in 2015 destroyer, and "X" was not considered the product with the base C2H5O-K+.

It makes a world of difference, if the smaller base was used X would be the minor product and more substituted Zaitsev would dominate. I would estimate the yield to be 85 percent.

Hope this helps

Dr. Romano

 

[dentalstudent2021]

It makes a world of difference, if the smaller base was used X would be the minor product and more substituted Zaitsev would dominate. I would estimate the yield to be 85 percent.

Hope this helps

Dr. Romano

Great, Thank you so much Dr. Romano. you have really enhanced the DAT learning experience for us!

 

[DAT Destroyer]

Great, Thank you so much Dr. Romano. you have really enhanced the DAT learning experience for us!

Always happy to help..keep banging away and feel free to post questions.

 

[FutureDent20]

Organic Chem Odyssey Chapter 14: #48
It said the answer is E. But how come it's not B? am I missing something?

 

[DAT Destroyer]

Organic Chem Odyssey Chapter 14: #48
It said the answer is E. But how come it's not B? am I missing something?

The typo was corrected......It is B. The solution to the problem is fine.....just the letter in the key should be indeed be B

 

[FutureDent20]

The typo was corrected......It is B. The solution to the problem is fine.....just the letter in the key should be indeed be B

Perfect! Thank you Dr. Romano

 

[gangazi]

Hello! I have a question about Ionic bond strength..

on 2016 dat destroyer gen chem,
#114) It says that melting pt of MgO is higher due to +2 and -2 leading to greater attraction...
however, I am confused because on
#243) It says that SrF2 is most ionic because they are located far away.

I dont remember why the discrepancies occur (MgO is closer to each other than NaCl in 114, so NaCl is more ionic so higher MP should be expected according to #243)
Can you explain why the discrepancies happen? Thank you orgoman