forming chiral centers question

[virtualmaster999]

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Hey everyone!

Kinda confused on this. So I thought that a chiral center is formed when you are making a change a specific carbon, but in this problem, it doesnt look like that:

"monochlorination of 2 methylbutane gives how many products, including stereochemistry?"

The answer is 6, but I thought it was 5. I guess when you chlorinate C1, you get a chiral center, in addition to the chiral center formed on C3.

So does this mean that "a chiral center is formed" on any carbon? It doesn't have to be the one where changes are being made i.e monochlorination?

Could someone clear this up for me? Thanks!

 

[FeralisExtremum]

I'm only getting 5 as well, for what it's worth. Chlorination on C1 (there are technically two equivalent carbons that can be C1 so they're only counted once), C2, C3 [creating R chirality], C3 [creating S chirality], and C4.

 

[virtualmaster999]

I'm only getting 5 as well, for what it's worth. Chlorination on C1 (there are technically two equivalent carbons that can be C1 so they're only counted once), C2, C3 [creating R chirality], C3 [creating S chirality], and C4.

Yup thats what I thought. This is Destroyer number 55 btw. I guess since chlorination on C1 causes a chiral center to form at C2, then it counts?

 

[BYU4you]

Hey everyone!

Kinda confused on this. So I thought that a chiral center is formed when you are making a change a specific carbon, but in this problem, it doesnt look like that:

"monochlorination of 2 methylbutane gives how many products, including stereochemistry?"

The answer is 6, but I thought it was 5. I guess when you chlorinate C1, you get a chiral center, in addition to the chiral center formed on C3.

So does this mean that "a chiral center is formed" on any carbon? It doesn't have to be the one where changes are being made i.e monochlorination?

Could someone clear this up for me? Thanks!

I don't quite understand the question you are asking but from what I can say to help is that usually the methyl coming off and C1 are "equivalent" and so c2 is not chiral. But once you add a chlorine to C1 it is no longer the same as the methyl group coming off so C2 becomes chiral now since it has 4 different substitutents.

If that doesn't help Dr Romano will be here shortly..

 

[virtualmaster999]

I don't quite understand the question you are asking but from what I can say to help is that usually the methyl coming off and C1 are "equivalent" and so c2 is not chiral. But once you add a chlorine to C1 it is no longer the same as the methyl group coming off so C2 becomes chiral now since it has 4 different substitutents.

If that doesn't help Dr Romano will be here shortly..

So a chiral center can be formed any place on the molecule?

 

[BYU4you]

So a chiral center can be formed any place on the molecule?

Any place that is affected by the addition of the chlorine. The terminal C4 isn't gaining any new substitutents by adding a chlorine at the end so it still isn't chiral. But C2 is affected.

 

[BYU4you]

Stars indicate chiral centers formed. Which is two hence enantiomers are also made.

So that is four products plus two enantiomers which makes six.

 

[510586]

I'm only getting 5 as well, for what it's worth. Chlorination on C1 (there are technically two equivalent carbons that can be C1 so they're only counted once), C2, C3 [creating R chirality], C3 [creating S chirality], and C4.

Doesn't chlroination on C1 cause the carbon 2 to become a chiral center (forming R and S chirality)?

 

[FeralisExtremum]

Ah, tricky. BYU4you is right, a chiral center is created even though it isn't on the carbon the chlorine is added to if we chlorinate C1. Good catch!

 

[virtualmaster999]

Thank you all!

 

[DAT Destroyer]

BYU4you,

Chlorination at C1 causes chirality at C2 !!! This was a bit tricky.....but examine ALL your isomeric products and check each one for chirality . Many times when a chlorine is installed into a molecule it generates a chiral center at that position......but NOT necessarily.

Hope this helps..

Dr. Romano

 

[virtualmaster999]

Orgo is fun but always has a few tricks up its sleeves!

 

[510586]

Ah, tricky. BYU4you is right, a chiral center is created even though it isn't on the carbon the chlorine is added to if we chlorinate C1. Good catch!

Sorry to bump this old thread, but adding the chlorine itself doesn't change the conformation of C2 right? It's more like C2 has the option of facing one way or the other so when you add a Cl it now has 2 options instead of being an achiral thing with 2 methyls coming off right? I believe other reactions don't generate a new chiral center like if it already is chiral (e.g carbon 2 already being wedge in an S conformation then adding Cl to something farther away would not change the wedge).

 

[FeralisExtremum]

Sorry to bump this old thread, but adding the chlorine itself doesn't change the conformation of C2 right? It's more like C2 has the option of facing one way or the other so when you add a Cl it now has 2 options instead of being an achiral thing with 2 methyls coming off right? I believe other reactions don't generate a new chiral center like if it already is chiral (e.g carbon 2 already being wedge in an S conformation then adding Cl to something farther away would not change the wedge).

Yea, chlorinating C1 basically creates 4 different substituents off of C1 whereas we used to have 2 identical methyl groups.

 

[510586]

Yea, chlorinating C1 basically creates 4 different substituents off of C1 whereas we used to have 2 identical methyl groups.

Oh actually I meant C2. Is it because there is free rotation so C2 can be an S or an R depending on how it rotates? That's why it's an enantiomer?

 

[FeralisExtremum]

Oh actually I meant C2. Is it because there is free rotation so C2 can be an S or an R depending on how it rotates? That's why it's an enantiomer?

Ah my bad. Chlorinating C2 doesn't create a chiral center at all, it's just considered a separate product (the question asks how many products can be formed, including stereoisomers - but that includes achiral products).

 

[510586]

Ah my bad. Chlorinating C2 doesn't create a chiral center at all, it's just considered a separate product (the question asks how many products can be formed, including stereoisomers - but that includes achiral products).

No I mean when you chlorinate c1 it causes C2 to become S or R right? Is it because when you chlorinate C1 you can chlorinate either methyl? Usually it wouldn't change the stereochemistry or create enantiomers when you do something to a side that's not on the chiral center right? Sorry for some reason it's not easy trying to describe it

 

[FeralisExtremum]

No I mean when you chlorinate c1 it causes C2 to become S or R right? Is it because when you chlorinate C1 you can chlorinate either methyl? Usually it wouldn't change the stereochemistry or create enantiomers when you do something to a side that's not on the chiral center right? Sorry for some reason it's not easy trying to describe it

Haha this is entirely my fault, no worries. When you chlorinate C1 it causes C2 to become a chiral center, which as you said can be S or R. I guess you could say it's because you can chlorinate either methyl - one of them would end up higher and the other lower in priority. Based on what substituents are wedged/dashed, the S/R chiral center could form (we don't know because it's not drawn out with wedged/dashes to determine - either outcome is possible).

The same applies to chlorinating C3 - chiral center is formed, and it could be S or R.

 

[510586]

Haha this is entirely my fault, no worries. When you chlorinate C1 it causes C2 to become a chiral center, which as you said can be S or R. I guess you could say it's because you can chlorinate either methyl - one of them would end up higher and the other lower in priority. Based on what substituents are wedged/dashed, the S/R chiral center could form (we don't know because it's not drawn out with wedged/dashes to determine - either outcome is possible).

The same applies to chlorinating C3 - chiral center is formed, and it could be S or R.

Oh ok. Well with c3 it is a bit different since the Cl can add to either side which is more standard. I think I am a bit unfamiliar with adding to the carbon. So normally if you added it and it was already chiral, it would not change chirality correct? Only because you are adding to a nonchiral turning into chiral does it turn chiral?

 

[DAT Destroyer]

Oh ok. Well with c3 it is a bit different since the Cl can add to either side which is more standard. I think I am a bit unfamiliar with adding to the carbon. So normally if you added it and it was already chiral, it would not change chirality correct? Only because you are adding to a nonchiral turning into chiral does it turn chiral?

OK...... Here is a simple approach to ALL these types of problems.

Keep in mind adding a chlorine atom to a carbon might allow for chirality at the EXACT carbon or ANOTHER r carbon. Simply replace a hydrogen with a single Cl to give 4 different isomers.
Correct ?
Now examine each one for an enantiomer. Be careful of C1. Placing a chlorine atom here generated chirality NEXT DOOR at C2 !!!!!!!!!!1-chloro -2-methylbutane is chiral at the second position. This is the isomer most often missed.

There would be a total of 6 total molecules made if all isomers including stereoisomers were counted.

I hope this helps.

Dr. Romano

 

[510586]

OK...... Here is a simple approach to ALL these types of problems.

Keep in mind adding a chlorine atom to a carbon might allow for chirality at the EXACT carbon or ANOTHER r carbon. Simply replace a hydrogen with a single Cl to give 4 different isomers.
Correct ?
Now examine each one for an enantiomer. Be careful of C1. Placing a chlorine atom here generated chirality NEXT DOOR at C2 !!!!!!!!!!1-chloro -2-methylbutane is chiral at the second position. This is the isomer most often missed.

There would be a total of 6 total molecules made if all isomers including stereoisomers were counted.

I hope this helps.

Dr. Romano

Oh OK so any time chirality is generated we alwaya get two different stereoisiners. Got it now thanks!