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!

 

[DAT Destroyer]

So they aren't considered the same? They're in the same position but the wedges and dashes swapped. When naming and counting it, couldn't you just count in the counterclockwise direction and come out with the same molecule? I cant tell why they arent equivalent.


Like 1-bromo-2-chlorobenzene can be drawn with be to the left of cl or vice versa and be the same molecule. Thanks for the help

1-bromo-2-chlorobenzene is NOT a chiral molecule.....no dashes or wedges needed, If a molecule is chiral......we employ these stereochemical designators. Please review STEREOCHEMISTRY !!! The Klein book has done a delightful job.

Hope this helps

Dr. Romano

 

[510586]

1-bromo-2-chlorobenzene is NOT a chiral molecule.....no dashes or wedges needed, If a molecule is chiral......we employ these stereochemical designators. Please review STEREOCHEMISTRY !!! The Klein book has done a delightful job.

Hope this helps

Dr. Romano

Oh ok they are enantiomers I was treating them as equivalents like if we were to name them. I understand that 1-bromo-2-chlorobenzene is not chiral. I mentioned it because I was trying to explain what I was thinking in terms of naming it clockwise or counterclockwise. I think I understand it now though. I thought some of the structures drawn were the same as each other, but meso is only a plane of symmetry on that same molecule not comparing 2 molecules. Thank you!

 

[GBP12]

DAT Destroyer O-Chem #78

I understand your logic for the answer, but would this logic be fine to arrive at the same answer? There are 5 peaks in the proton NMR and the only compound that would give 5 peaks would be B making it the right answer?

 

[GBP12]

DAT Destroyer O-Chem #85

Is the reason the Bromine adds to the isopropyl group because the H on that carbon is more acidic than the H coming off the ortho or para positions on the ring, and if so, what makes it more acidic?

 

[510586]

In number 88 of OC destroyer, why is the Cl coming off the para the major product as opposed to the ortho?

 

[510586]

DAT Destroyer O-Chem #85

Is the reason the Bromine adds to the isopropyl group because the H on that carbon is more acidic than the H coming off the ortho or para positions on the ring, and if so, what makes it more acidic?

Br2/hv replaces the benzylic H with a Br, as that position is more stable than a H directly on the benzene. In this case the only benzylic H is the one coming off the isopropyl adjacent to the ring. Unless there is an alkene, then there will be a mix of products if I'm not mistaken.

 

[DAT Destroyer]

In number 88 of OC destroyer, why is the Cl coming off the para the major product as opposed to the ortho?

The ortho is the minor product,,,,,the para position is wide open.......much less sterically hindered.

Dr. Romano

 

[510586]

The ortho is the minor product,,,,,the para position is wide open.......much less sterically hindered.

Dr. Romano

Got it thanks!

 

[DAT Destroyer]

Got it thanks!

🙂

 

[T402]

I just want to say thank you so much Dr. Romano! These answers are really clarifying things. It is so nice of you to go out of your way to help!!

 

[DAT Destroyer]

I just want to say thank you so much Dr. Romano! These answers are really clarifying things. It is so nice of you to go out of your way to help!!

I am responding for Dr. Romano and thank you for acknowledging his hard work. He is currently in lecture with his summer DAT students but will respond personally soon. And answer any questions that need answering.

Thanks again..

Nancy

 

[GBP12]

O-Chem #108/109

I know in E2 reactions the leaving group and the H have to be anti-coplanar and that will determine where the newly formed double bond will reside but in these two problems how do you know that the answers given are going to be where the double bond is? Like in 108, why couldn't the double bond be in the ring, wouldn't the Br and H be anti-coplanar?

Also on 109, why would the double bond form between where the Cl/CH3 are? Why not to the left of the Cl?

 

[DAT Destroyer]

O-Chem #108/109

I know in E2 reactions the leaving group and the H have to be anti-coplanar and that will determine where the newly formed double bond will reside but in these two problems how do you know that the answers given are going to be where the double bond is? Like in 108, why couldn't the double bond be in the ring, wouldn't the Br and H be anti-coplanar?

Also on 109, why would the double bond form between where the Cl/CH3 are? Why not to the left of the Cl?

For #108...we employed a Big Bulky base after bromination.....,,the only option for the major product is removal of the most accessible proton, namely the CH3 hydrogen.

For 109...Good point.....HOWEVER.....since no stereochemistry is implied,,,,ALWAYS show the Zaitsev product if a strong. reasonably-sized base is employed . If Stereochemistry was shown.....then the groups must be anti-periplanar.

Problem #152 will make you happier.

Hope this helps

Dr. Romano

 

[Sigg]

DAT Destroyer (2015) Ochem question 63.

I'm a little lost with the second step in this reaction. How did the C2H5I manage to get onto the cyclohexane, and where did the amine compound go? What exactly is the mechanism here (what kind of reaction is this?)

Thanks in advance for any help!

 

[DAT Destroyer]

DAT Destroyer (2015) Ochem question 63.

I'm a little lost with the second step in this reaction. How did the C2H5I manage to get onto the cyclohexane, and where did the amine compound go? What exactly is the mechanism here (what kind of reaction is this?)

Thanks in advance for any help!

This is a very classic reaction seen in Organic Chemistry 2. I have first formed an enamine......we protonate the Oxygen.....attack with the amine.....and set WATER up as our leaving group. Once we get the enamine,,,,,,,the fun begins......It will act as a potent NUCLEOPHILE forming the acyl iminium salt intermediate......which hydrolyzes to the product choice B. Any Organic text shows this nicely.

For the DAT.....you will not have time to work out the mechanism.....thus set it up as I have shown to solve it in a matter of seconds.

Dr. Romano

 

[Sigg]

DAT Destroyer (2015) Ochem Question 92

I understand why A is the answer and can yield an alkene, but I was looking through the other options...and was wondering why C would even react.

Isn't Cl- a poorer leaving group in comparison to I-? If I- attempts to displace Cl- via an SN2 reaction, would it even proceed? Since I- is a much weaker conjugate base (correct me if I'm wrong?), it's a better leaving group than Cl-, so I would assume it wouldn't be strong enough to displace Cl-
So I'm just wondering about whether this SN2 reaction would even proceed?

Thanks!

 

[510586]

This isn't a very important question, but isn't the menstrual phase the final phase of the menstrual cycle, not the secretory phase?

 

[510586]

Why does meiosis decrease the chromosome number? the chromosome number in a parent cell before division is 46 (or 92 chromatids), and it finishes out with 23 in each daughter cell. Aren't there 4 daughter cells which means there are still a total of 92?

 

[cacajuate]

Why does meiosis decrease the chromosome number? the chromosome number in a parent cell before division is 46 (or 92 chromatids), and it finishes out with 23 in each daughter cell. Aren't there 4 daughter cells which means there are still a total of 92?

Each daughter cell is haploid, hence being less. You don't add it up after they have split, since they are now their own independent gamete.

 

[DAT Destroyer]

Why does meiosis decrease the chromosome number? the chromosome number in a parent cell before division is 46 (or 92 chromatids), and it finishes out with 23 in each daughter cell. Aren't there 4 daughter cells which means there are still a total of 92?

Yes. There are a total of 92 chromosomes, but they are divided among 4 daughter cells. Each daughter cell now has 23 chromosomes (not pairs). So, the phrase "decreases the number of chromosomes" only means less chromosomes per each cell, not in total.

Hope this helps..

Nancy

 

[cacajuate]

DAT Destroyer (2015) Ochem Question 92

I understand why A is the answer and can yield an alkene, but I was looking through the other options...and was wondering why C would even react.

Isn't Cl- a poorer leaving group in comparison to I-? If I- attempts to displace Cl- via an SN2 reaction, would it even proceed? Since I- is a much weaker conjugate base (correct me if I'm wrong?), it's a better leaving group than Cl-, so I would assume it wouldn't be strong enough to displace Cl-
So I'm just wondering about whether this SN2 reaction would even proceed?

Thanks!

You are reading too far into it. I- is a strong nucleophile and Cl- is a good leaving group, that's all there is to it.

 

[Sigg]

You are reading too far into it. I- is a strong nucleophile and Cl- is a good leaving group, that's all there is to it.

Thanks cacajuate, I figured I might have been...I tend to do that a lot when studying. I just wanted to see if what I was thinking made any sense

 

[cacajuate]

Bio '15 Questions #196 and #253

Question #196 says crocodile in incorrectly matched with a 3 chamber heart and then #253 says reptiles have a 3 chamber heart.

Feralis taxonomy cheat sheet says it has a 3 chamber heart. So what is it?

 

[Sigg]

Bio '15 Questions #196 and #253

Question #196 says crocodile in incorrectly matched with a 3 chamber heart and then #253 says reptiles have a 3 chamber heart.

Feralis taxonomy cheat sheet says it has a 3 chamber heart. So what is it?

Hey cacajuate, crocs/alligators are the exception! They're the only reptiles with a 4 chamber heart...This is worth knowing. I think it's actually in Feralis Bio notes as well (ctrl F "crocs/gators")

Edit: Just did it, its on pg 40 of feralis

 

[DAT Destroyer]

DAT Destroyer (2015) Ochem Question 92

I understand why A is the answer and can yield an alkene, but I was looking through the other options...and was wondering why C would even react.

Isn't Cl- a poorer leaving group in comparison to I-? If I- attempts to displace Cl- via an SN2 reaction, would it even proceed? Since I- is a much weaker conjugate base (correct me if I'm wrong?), it's a better leaving group than Cl-, so I would assume it wouldn't be strong enough to displace Cl-
So I'm just wondering about whether this SN2 reaction would even proceed?

Thanks!

Choice C in Problem #92 is the famous FINKELSTEIN reaction !!!! Iodine is a great nucleophile......and Chloride,,,,although not the best leaving group on the planet is perfectly fine,,,,,,This is a classic SN2 reaction.

Lets show the Finkelstein reaction some Love !🙂

Hope this helps....

Dr. Romano

.

 

[Drenalin]

On problem 380 bio (2015),
Question: Which is true regarding Acetylcholinesterase?
answer says: It is located on the post-synaptic membrane and terminates the signal transmission by hydrolyzing acetylcholine

However wouldn't acetylcholinesterase be located in the synaptic cleft since it is an enzyme and the acetylcholine receptors be located on the post-synaptic membrane?

 

[510586]

On number 111 OC 2015, why is the product not just 1 D added to the alpha H? Isn't DCl acidic conditions? When I learned it in class, D2O and D+ yielded 1 D on the most acidic position.

 

[cacajuate]

On number 111 OC 2015, why is the product not just 1 D added to the alpha H? Isn't DCl acidic conditions? When I learned it in class, D2O and D+ yielded 1 D on the most acidic position.

its because the ketone tautomerizes and each time the enol is formed it removes an alpha hydrogen and replaces with D. It will convert back and forth b/w the enol and ketone form and each time another D is added.

 

[510586]

its because the ketone tautomerizes and each time the enol is formed it removes an alpha hydrogen and replaces with D. It will convert back and forth b/w the enol and ketone form and each time another D is added.

How come it doesn't do that for say Br2/CH3COOH(acid)? It only adds one halogen in that case. What makes the D different, if it is?

 

[DAT Destroyer]

On number 111 OC 2015, why is the product not just 1 D added to the alpha H? Isn't DCl acidic conditions? When I learned it in class, D2O and D+ yielded 1 D on the most acidic position.

The problem involves a deuterium exchange,,,,,,,,we replace an H for a D...the problem states EXCESS......thus all the H's must be replaced......via an enolate intermediate. Consult any Orgo text for details.

Dr. Romano

 

[510586]

The problem involves a deuterium exchange,,,,,,,,we replace an H for a D...the problem states EXCESS......thus all the H's must be replaced......via an enolate intermediate. Consult any Orgo text for details.

Dr. Romano


View attachment 192735

Oh I understand now thanks. So would excess Br2 / H3O+ do the same thing? Br adding multiple times to the alpha H while the H2O part takes out the enol H?

 

[DAT Destroyer]

Oh I understand now thanks. So would excess Br2 / H3O+ do the same thing? Br adding multiple times to the alpha H while the H2O part takes out the enol H?

Normally if we use acid, a single bromine attaches. The same goes for base. However, if you have a methyl ketone in a basic solution you would do the Haloform reaction.

Dr. Romano

 

[510586]

Normally if we use acid, a single bromine attaches. The same goes for base. However, if you have a methyl ketone in a basic solution you would do the Haloform reaction.

Dr. Romano

Got it so I guess this is just a special D2O case then. If this was say a secondary alpha carbon it would add two D's if in excess as well right? This isn't just for methyl ketones either?

 

[DAT Destroyer]

Got it so I guess this is just a special D2O case then. If this was say a secondary alpha carbon it would add two D's if in excess as well right? This isn't just for methyl ketones either?

Yes......Normally we deuterate all the Hs. Yes,,,,,all ketones and aldehydes ...alpha or not would add a single halogen. This is an important step when doing an organic synthesis. For example.....If cyclohexanone was brominated in acid or base.....we would get 2-bromocyclohexanone as our product. If deuterated in excess acid or base....we would get the TETRADEUTERATED cyclohexanone.

Hope this helps.

 

[510586]

Yes......Normally we deuterate all the Hs. Yes,,,,,all ketones and aldehydes ...alpha or not would add a single halogen. This is an important step when doing an organic synthesis. For example.....If cyclohexanone was brominated in acid or base.....we would get 1-bromocyclohexanone as our product. If deuterated in excess acid or base....we would get the TETRADEUTERATED cyclohexanone.

Hope this helps.

Alright. I think you mean 2-bromocyclohexanone but I understand. Thank you for your help!

 

[m145491]

On number 67 OChem 2015, why does the Cl rearrange when the reactant is put with HCl? Since the reactant is a primary alcohol, I though rearrangements could not occur since it goes through a SN2 reaction, hence there is no carbocation? Does it have something to do with the ZnCl2 catalyst since it is not present with the HCl in the answer choice?

 

[510586]

So in Ferali's notes, it says that "
o Difference because prokaryotes have no mitochondria so they (unlike eukaryotes) don’t need to transfer the two NADH molecules into the mitochondrial matrix (which is done via active transport thus costing 1 ATP each), they just use cell membrane for respiration.

However, the explanation for RBC not undergoing the Krebs cycle in question 182 is that they don't have mitochondria. How come prokaryotes can do the Kreb's cycle without mitochondria (using their cell membrane) but RBC can't?

 

[DAT Destroyer]

On number 67 OChem 2015, why does the Cl rearrange when the reactant is put with HCl? Since the reactant is a primary alcohol, I though rearrangements could not occur since it goes through a SN2 reaction, hence there is no carbocation? Does it have something to do with the ZnCl2 catalyst since it is not present with the HCl in the answer choice?

Primary alcohols usually do not do SN1 reactions.....BUT look closer......we have branching. It turns out......that once protonated.....the group leaves at the same times as a shift occurs !!!!

This is a concerted hydride shift....fairly common with primary alcohols that have branching nearby . Indeed...this avoids forming the dreaded primary carbocation.....but a very stable tertiary........once formed.....we can then attack to form the 2-chloro-2-methylpropane isomer. Clearly.....this is not an SN2 process,,,,,,but rather Sn1-like. Several books such as Francis Carey PhD illustrates similar examples.

For instance.....if we add acid to 1-butanol...we get a mixture of 1 and 2 butene isomers. Why ? Protonate the primary alcohol.....even though no branching.......a simultaneous shift could lead to a secondary carbocation...which can give the 2-butene isomer.

Thus.....as you can see,,,,,,A primary alcohol is best halogenated with SOCl2, PCl3 or similar reagents to prevent any molecular rearrangements. If HCl is used....the reaction is sluggish...hence we use ZnCl2 as a Lewis acid catalyst.

I hope this helps....as I found it fun even explaining this to you !

Keep up the good work.

Dr. Jim Romano

 

[510586]

Is number 116 of the GC destroyer doable using a simple Le Chatlier? Or is nernst still the best?

 

[universalforceps]

I'm going through the DAT Destroyer biology, and I had a question about number 290. The answer for the question was that all are true statements, however, I remember from animal physiology and looking back at my notes, that norepinephrine and acetylcholine are neurotransmitters of the sympathetic nervous system whereas acetylcholine is the only neurotransmitter of the parasympathetic nervous system.

One of the statements that was deemed true stated: Norepinephrine is the primary neurotransmitter of the sympathetic nervous system.

By primary, does it mean the first neurotransmitter? I thought that would be acetylcholine since it acts on the nicotinic receptor. If someone could help clarify this, that'd be great.

 

[DAT Destroyer]

On problem 380 bio (2015),
Question: Which is true regarding Acetylcholinesterase?
answer says: It is located on the post-synaptic membrane and terminates the signal transmission by hydrolyzing acetylcholine

However wouldn't acetylcholinesterase be located in the synaptic cleft since it is an enzyme and the acetylcholine receptors be located on the post-synaptic membrane?

Acetylcholinesterase is located on the post-synaptic membrane, close to the post-synaptic receptor, in order to ensure quick deactivation of acetylcholine.

 

[DAT Destroyer]

Is number 116 of the GC destroyer doable using a simple Le Chatlier? Or is nernst still the best?

Indeed so..... it is an equilibrium process. The most important thing here to understand is the relationship of E to concentration. Q is the thermodynamic reaction quotient which has the same form as the equilibrium constant , except that the concentrations and gas pressures are those that exist in a reaction mixture at a given instant. Don't not let the Nernst equation scare you. UNDERSTANDING why it is used is the most important thing a student taking the DAT needs.

Here is the bottom line.....We usually focus on reactant and products in their standard states.....pH=7...all concentrations at 1M, all gases at 1atm........but standard states are often difficult to measure, and sometimes even IMPOSSIBLE !!!!

If you do dental research, and need to calculate voltage generated by a metal and how it interacts with pulpal tissue,,,,,,the Nernst equation would be used.

I hope this helps.

Dr. Romano

 

[syedj94]

I have the 2013 Destroyer and I have a question about OCHEM #2
Why are there only 3 monobrominated products?

 

[GBP12]

I think where the double bond goes on Elimination reactions is screwing me up.

I get that the more substituted product will be formed as long as it is anti-coplanar for the E2 mechanism but on problem #170 for Destroyer O-Chem, why is the double bond formed where it is? Wouldn't the more substituted alkene be if the double bond was in the middle, and can't it still be anti-coplanar with the Cl and a H so why wouldn't it form?

 

[cacajuate]

I think where the double bond goes on Elimination reactions is screwing me up.

I get that the more substituted product will be formed as long as it is anti-coplanar for the E2 mechanism but on problem #170 for Destroyer O-Chem, why is the double bond formed where it is? Wouldn't the more substituted alkene be if the double bond was in the middle, and can't it still be anti-coplanar with the Cl and a H so why wouldn't it form?

The double bond is formed on the less sub side because of the big bulky base that is used.

 

[510586]

So in Ferali's notes, it says that
o Difference because prokaryotes have no mitochondria so they (unlike eukaryotes) don’t need to transfer the two NADH molecules into the mitochondrial matrix (which is done via active transport thus costing 1 ATP each), they just use cell membrane for respiration.

However, the explanation for RBC not undergoing the Krebs cycle in question 182 is that they don't have mitochondria. How come prokaryotes can do the Kreb's cycle without mitochondria (using their cell membrane) but RBC can't? Don't mean to post this twice but I was asked to.

 

[cacajuate]

So in Ferali's notes, it says that
o Difference because prokaryotes have no mitochondria so they (unlike eukaryotes) don’t need to transfer the two NADH molecules into the mitochondrial matrix (which is done via active transport thus costing 1 ATP each), they just use cell membrane for respiration.

However, the explanation for RBC not undergoing the Krebs cycle in question 182 is that they don't have mitochondria. How come prokaryotes can do the Kreb's cycle without mitochondria (using their cell membrane) but RBC can't? Don't mean to post this twice but I was asked to.

I think you are confusing Krebs cycle and ETC. Prokaryotes do have ETC which they use for respiration. RBC definitely do not have a mitochondria, they use glycolysis for energy needs.

 

[510586]

I think you are confusing Krebs cycle and ETC. Prokaryotes do have ETC which they use for respiration. RBC definitely do not have a mitochondria, they use glycolysis for energy needs.

Then how do they generate as much ATP / more than eukaryotes? Just a super duper version of glycolysis? Because glycolysis doesn't make that much ATP, and Krebs makes a lot of the nadh and fadh2 that goes into oxidative phosphorylation

 

[cacajuate]

Dont quote me on this, you'll need to look it up but I believe energy is wasted moving the molecules into mito. ask @FeralisExtremum, I know he knows

 

[StudentDoc1234]

Then how do they generate as much ATP / more than eukaryotes? Just a super duper version of glycolysis? Because glycolysis doesn't make that much ATP, and Krebs makes a lot of the nadh and fadh2 that goes into oxidative phosphorylation

Prokaryotes do generate ATP with Krebs cycle too except unlike euk. it takes place in the cytosol NOT the cell membrane (prokaryotes use the cell membrane as the electron transport chain).