Isomers, Chad's vid doesn't explain all...

[babowc]

Advertisement - Members don't see this ad

So, Chad doesn't explain conformational, geometric, configurational..

Has anyone seen these on the DAT?
I've seen it a few times on practice tests, but can't remember whether I saw it on the real thing...

 

[aznnytezx]

I am not too sure about chad's video about isomers, but as you know that isomers are same number of elements, but different molecules. There are isomers that are structural, depending the placement of a functional group. A good example will be alpha glucose and beta glucose, where alpha glucose have the OH placed straight down from the first carbon, while the beta glucose is placed above the first carbon.

For geometric, it depends on the double bonds. So you can think of (E or Z) or cis or trans, because it makes the molecule chemically different.

For enantiomers it is also the same thing.

For identifying it, it is really easy. I just explained to you. For enantiomers, you can just look for the mirror image. For structural isomers, you can look for molecules that are arranged differently through their spatial settings. Also for geometrically, look for present of double bonds. Goodluck!

 

[bluemoon27]

I thought he does have a video on isomers though...maybe I dont understand if you were looking for something specific thought.

 

[babowc]

Hm.. I'm still a bit confused on the entire thing..

1.Enantiomers are mirror images, yet not superimposable. Right?
2. But chiral molecules are mirror images, and not superimposable. So do(are) all chiral molecules enantiomers?..
3. Diastereomers have NO mirror image, but it is a stereoisomer.. so diastereomers cannot be chiral nor achiral?

On his videos, Chad states that

If 2 chiral centers are different, they're enantiomers
and if only 1 chiral center is different, they're diastereomers

I might just be thick.. but I don't get it 😳

 

[bluemoon27]

I think you may need to watch that video again from chad. I had to watch it thrice before it clicked.

But when you talk about an object, if you say its chiral, that means that this object and its mirror image are not superposable. Chiral is a property that can be determined for every object when you look at that object just by itself.

But for enantiomers and diastereomers, thats a comparison BETWEEN two molecules they give you in the problem. You cant just say A is an enantiomer, you have to say A is enantiomer to something, say for instance B. You look at every chiral center in both molecules to determine which configuration it is R or S. If you look at chiral centers in one and it has one set of R/S configurations at its chiral centers and the other molecule has exactly the opposite at each chiral center (so essentially the R and S are flip at EVERY chiral center), and they look like nonsuperposable mirror image, then thats an enantiomer. If the two molecules have one place where the chiral center is different but the rest of the chiral centers same and its not a mirror image at all, then its a diastereomer.

I just remember that if its a nonsuperposable mirror image then enantiomer. if not a mirror image at all, then diastereomer.

cis/trans isomers are examples of diastereomers.

stereoisomers have different 3d orientation of the groups in space. so both enantiomers and diastereomer = stereoisomers.

Hope this helps!

 

[babowc]

Another question..
do ALL ACHIRAL molecules NOT have chiral centers?

 

[bluemoon27]

they can have chiral centers and still be achiral. Example is the meso compounds which have an internal mirror plane. The molecule is symmetric and that results in the molecule not rotating plane polarized light. So meso is one of the classic example of how you can have Chiral center and still be ACHIRAL.

but yea just watch Chad and do ochem odyssey. thats what i did and it has helped me a lot! i dont have a very firm foundation myself but i watch videos and practice it out on the problems and after few problems it will start making sense. I know this stuff can get pretty tough at times, but just hang in there and do lots of probs.

This may help.

http://www.chem.ucla.edu/harding/ec_tutorials/tutorial17.pdf

 

[babowc]

example..

The molecule on the leftis a Meso,
where as the one on the right is "ACHIRAL"?

 

[babowc]

OOOOOOOOOOOOHHHHHHHHHHHHHHHHHH

I think I get it!

 

[bluemoon27]

I think you meant to say the one on the left is meso, and yes it is because of the inernal mirror plane. so the meso ones is achiral.

the one on the right doesnt have a chiral center. remember you must have 4 different substituents to be classified as a chiral center. here, you have three methyl groups, and a F, so 2 different substituents and not 4.

so both are achiral, but because of different reasons.

im glad you get it! explaining it to you is actually helping me to review it as well haha! =)

 

[babowc]

Yes, that's what I meant,
sorry, haha.
My brain is burned out.. not good

Thanks a bunch.. I was stuck on this for a bit.. I'll do some more practice and see where I stand

 

[babowc]

I think you meant to say the one on the left is meso, and yes it is because of the inernal mirror plane. so the meso ones is achiral.

the one on the right doesnt have a chiral center. remember you must have 4 different substituents to be classified as a chiral center. here, you have three methyl groups, and a F, so 2 different substituents and not 4.

so both are achiral, but because of different reasons.

im glad you get it! explaining it to you is actually helping me to review it as well haha! =)

One more question..

"not chiral" is the same thing as achiral?

edit:
To my summation...

chiral - not mirror images, not superimposable, and contains chiral center (4 different groups)
--enantiomer - ARE mirror images, not superimposable, contains chiral centers, and generally has a difference in ALL R/S configuration
--diastereomer - NOT mirror images, has chiral centers, and generally has only ONE difference in R/S configuration
achiral - mirror images, superposable, DOES NOT contain chiral centers
--meso - an achiral molecule, with a chiral center, OR line of symmetry

Does that seem right?
I can listen to lectures and watch Chad all day, but I feel like if I get it in my own words, I can retain it a lot better

 

[bluemoon27]

yup! so essentially achiral compounds ARE superposable with their mirror image whereas chiral ones are NOT. recall chads example of the white q ball for pool. its a plain old white ball. in the mirror image, looks exactly the same as the orginial q ball, so thats an achiral example.

one trick to remember. if you see "a" in front of some words and you also know the word without the a as well, then "aword" means "not" of the word. examples include achiral, asymmetric, even common words like atypical. i know this applies to a lot of stuff in bio, but i cant think of another good example top of my head right now.

 

[bluemoon27]

one more thing. poster at the top said diastereomers can result only when you have double bond. although that is one case with the cis/trans isomers, even if you dont have double bond, you have still have diastereomers.

 

[yoRo]

when do. u have ur test

 

[babowc]

in 4 days..
I'm reviewing now, and it just stuck out like a sore thumb, so I had to understand it before delving further.

 

[yoRo]

in 4 days..
I'm reviewing now, and it just stuck out like a sore thumb, so I had to understand it before delving further.

ohh ok. just make sure u get some practice on this. i dont remember seeing that many queestions on it...

 

[babowc]

ohh ok. just make sure u get some practice on this. i dont remember seeing that many queestions on it...

That's gooooood, haha.
But I just wasted a couple hours on it 👎
Time to knock out everything else!