Question before the big day!

[_a_rose2238]

Okay Guys,

DAT tomorrow. I feel like I am as ready as I am going to be. I am obviously super nervous but you all suggested so much QR material that I have dedicated a ton of time to. I feel so much better about it now.

I was wondering if anyone had any insight on a question I wanted to get cleared up before going into the exam.

For Ochem:
Enantiomers have individual optical activity but they cancel each other out. I get this. But as I was going back through the bootcamp tests yesterday I found two questions that seem to contradict each other. One says that enantiomers are optically active and the other implies they are not optically active.
If a question simply asks: Are enantiomers optically active? The answer would be "no", right? I feel like this is something that is super likely to show up so I don't want to get it wrong for stupid reasons lol


I know there are a couple of people taking it tomorrow as well so GOOD LUCK

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[Steeezy]

Good question! I'd say that unless specified that the mixture of enantiomers is racemic (50/50) then the answer would be that it is optically active. Enantiomers on their own are optically active, and when mixed together in unequal amounts, the mixture is also optically active.

 

[DDSDCMUU]

So I actually think it would optically inactive. The two enantiomers would cancel each other out. That is what Dr. Mike said on DAT BC videos if I remember correctly. Maybe @orgoman22 can clarify this?

 

[KatawareDoki]

I've come across those exact two scenarios. How I understand it is like this:

Individually, they are optically active and hold some "+" or "-" value in a particular rotation.
When you have them mixed together at equal amounts, their NET value would be "0" since one would rotate "+44.3" and one would be "-44.3" when we're talking about a pair of enantiomers.

Again, I could be wrong, but with this thought process, I've been able to come up with correct answer choices. Cheers!

 

[_a_rose2238]

I've come across those exact two scenarios. How I understand it is like this:

Individually, they are optically active and hold some "+" or "-" value in a particular rotation.
When you have them mixed together at equal amounts, their NET value would be "0" since one would rotate "+44.3" and one would be "-44.3" when we're talking about a pair of enantiomers.

Again, I could be wrong, but with this thought process, I've been able to come up with correct answer choices. Cheers!

This is what I was thinking. I'm hoping they won't ask it in a confusing way. Because technically they are but together they aren't. I guess with this logic it would simply be: No. enantiomers are not optically active.

 

[DDSDCMUU]

This is what I was thinking. I'm hoping they won't ask it in a confusing way. Because technically they are but together they aren't. I guess with this logic it would simply be: No. enantiomers are not optically active.

Yeah I think it would have to say "pure enantiomer" or only s. Good luck on your DAT! You will rock it!

 

[_a_rose2238]

So I actually think it would optically inactive. The two enantiomers would cancel each other out. That is what Dr. Mike said on DAT BC videos if I remember correctly. Maybe @orgoman22 can clarify this?

I watched that as well! And that's is the logic I've been sticking with until I found question 12 on exam 9. In the description it says that they are active.

 

[DDSDCMUU]

I personally would go with inactive unless pure. Good luck

 

[deleted678432]

Chiral compounds (besides meso compounds) are optically active. This means that an enantiomer is optically active. When there is a racemic mixture (50% R/50% S), then the enantiomers are STILL optically active, but the overall mixture would have NO rotation in a polarimeter. To reiterate.. say that molecule I has light rotation of +20. This means that its enantiomer has a light rotation of -20. When the two are mixed together in an exact 50/50 racemic mix, each molecule STILL exhibits optical activity INDIVIDUALLY but the overall solution would have an overall rotation of 0.00.

 

[DAT Destroyer]

Okay Guys,

DAT tomorrow. I feel like I am as ready as I am going to be. I am obviously super nervous but you all suggested so much QR material that I have dedicated a ton of time to. I feel so much better about it now.

I was wondering if anyone had any insight on a question I wanted to get cleared up before going into the exam.

For Ochem:
Enantiomers have individual optical activity but they cancel each other out. I get this. But as I was going back through the bootcamp tests yesterday I found two questions that seem to contradict each other. One says that enantiomers are optically active and the other implies they are not optically active.
If a question simply asks: Are enantiomers optically active? The answer would be "no", right? I feel like this is something that is super likely to show up so I don't want to get it wrong for stupid reasons lol


I know there are a couple of people taking it tomorrow as well so GOOD LUCK

Enantiomers are optically active substances that have the ability to rotate the plane of polarized light. They are indeed optically active. If a reaction gives you a reacemic mixture of these enantiomers, however it would be inactive. Truth be known, rarely in real life do we get a 50-50 mixture....often the numbers are a bit different. In advanced organic chemistry we like to call it a scalemic mixture. To answer your question......YES...they are indeed optically active. Hope this helps.

 

[DDSDCMUU]

How did your DAT go?