Chemistry: Post your doubts here!

[Konstantino Nikolas]

http://www.chemguide.co.uk/basicorg/isomerism/cholesterol.gif
How do I identify the chiral carbon atom?
Ty in advance..

Those numbers indicate the chiral carbons right? But I am pretty sure number 9 is not a chiral carbon ... 1 to 8 are though

 

[Iris Dylan Lane]

Those numbers indicate the chiral carbons right? But I am pretty sure number 9 is not a chiral carbon ... 1 to 8 are though

Yeah they do..but how am I supposed to know?

 

[Konstantino Nikolas]

Yeah they do..but how am I supposed to know?

Consider a single Carbon atom. First, make sure that the Carbon has four bonds connected to it. If not, then draw the extra bonds and add the hydrogen.
Let's take Carbon 1 as our example.

Now, consider the groups attached to that Carbon. There is an - H, - OH. That much is obvious. Then look at the GROUPS attached on both sides. A common mistake is to just consider the Carbon ATOMS attached on either side and claiming the carbon to be a non-chiral centre. When you see the group on one either side, they are different (You know this because if you split the whole compound at that carbon, the two sides will not be symmetrical). So 4 different groups attached to Carbon 1. Therefore, Carbon 1 is a chiral centre.

If you repeat this with every other numbered Carbon, you will realise that Carbon 1 to Carbon 8 are chiral. However, Carbon 9 is not a chiral carbon because it has two CH3 groups bonded to it.

Hope you understand.

 

[Konstantino Nikolas]

View attachment 59599

Consider a single Carbon atom. First, make sure that the Carbon has four bonds connected to it. If not, then draw the extra bonds and add the hydrogen.
Let's take Carbon 1 as our example.

Now, consider the groups attached to that Carbon. There is an - H, - OH. That much is obvious. Then look at the GROUPS attached on both sides. A common mistake is to just consider the Carbon ATOMS attached on either side and claiming the carbon to be a non-chiral centre. When you see the group on one either side, they are different (You know this because if you split the whole compound at that carbon, the two sides will not be symmetrical). So 4 different groups attached to Carbon 1. Therefore, Carbon 1 is a chiral centre.

If you repeat this with every other numbered Carbon, you will realise that Carbon 1 to Carbon 8 are chiral. However, Carbon 9 is not a chiral carbon because it has two CH3 groups bonded to it.

Hope you understand.

And the Carbons that are not numbered have either a double bond or have two Hydrogen atoms bonded to them. So they are fairly easy to eliminate from our list of chiral carbons.

 

[Iris Dylan Lane]

View attachment 59599

Consider a single Carbon atom. First, make sure that the Carbon has four bonds connected to it. If not, then draw the extra bonds and add the hydrogen.
Let's take Carbon 1 as our example.

Now, consider the groups attached to that Carbon. There is an - H, - OH. That much is obvious. Then look at the GROUPS attached on both sides. A common mistake is to just consider the Carbon ATOMS attached on either side and claiming the carbon to be a non-chiral centre. When you see the group on one either side, they are different (You know this because if you split the whole compound at that carbon, the two sides will not be symmetrical). So 4 different groups attached to Carbon 1. Therefore, Carbon 1 is a chiral centre.

If you repeat this with every other numbered Carbon, you will realise that Carbon 1 to Carbon 8 are chiral. However, Carbon 9 is not a chiral carbon because it has two CH3 groups bonded to it.

Hope you understand.

Yes I got it. Thank you so much. I really appreciate it
What if there were 6 C atoms in a ring, and one was bonded to CH3 and H? Is that C atom chiral?

 

[qwertypoiu]

Yeah they do..but how am I supposed to know?

Konstantino Nikolas already gave an excellent answer. I just wanna add one point.

To make it quick to find chiral carbons from a skeletal formula, you can find carbons from which at least 3 lines are coming out. The points (carbons) from which two lines are coming out (ie. The line just bent to form a vertex) must have 2 hydrogen atoms attached to it, so it could never be chiral. Furthermore, you should ignore any carbon attached to double bonds. This should help you find chiral centres quicker.

Of course, you still have to make sure there aren't two same groups attached to a carbon even if there are three lines coming out of it, like in the case of carbon number 9 in the above example.

 

[Konstantino Nikolas]

Yes I got it. Thank you so much. I really appreciate it
What if there were 6 C atoms in a ring, and one was bonded to CH3 and H? Is that C atom chiral?

No problem.
Only a 6 Carbon ring with nothing else attached? f that is the case, then it wouldn't be a chiral centre.

 

[Iris Dylan Lane]

Konstantino Nikolas already gave an excellent answer. I just wanna add one point.

To make it quick to find chiral carbons from a skeletal formula, you can find carbons from which at least 3 lines are coming out. The points (carbons) from which two lines are coming out (ie. The line just bent to form a vertex) must have 2 hydrogen atoms attached to it, so it could never be chiral. Furthermore, you should ignore any carbon attached to double bonds. This should help you find chiral centres quicker.

Of course, you still have to make sure there aren't two same groups attached to a carbon even if there are three lines coming out of it, like in the case of carbon number 9 in the above example.

Hahah okay..that's a really good point too. Thank you!

 

[Konstantino Nikolas]

Konstantino Nikolas already gave an excellent answer. I just wanna add one point.

To make it quick to find chiral carbons from a skeletal formula, you can find carbons from which at least 3 lines are coming out. The points (carbons) from which two lines are coming out (ie. The line just bent to form a vertex) must have 2 hydrogen atoms attached to it, so it could never be chiral. Furthermore, you should ignore any carbon attached to double bonds. This should help you find chiral centres quicker.

Of course, you still have to make sure there aren't two same groups attached to a carbon even if there are three lines coming out of it, like in the case of carbon number 9 in the above example.

Yupp. That comes with practice ... though it used to be difficult to comprehend the whole compound before knowing how to do it.

 

[Iris Dylan Lane]

No problem.
Only a 6 Carbon ring with nothing else attached? f that is the case, then it wouldn't be a chiral centre.

Yes nothing else. K..thanks

 

[Konstantino Nikolas]

Yes nothing else. K..thanks

Because it would be symmetrical if you split the compound. No problem.

 

[Iris Dylan Lane]

Because it would be symmetrical if you split the compound. No problem.

Stupid question, but could you tell me what's attached to that carbon atom other than the CH3 and H? Do you consider it to be the rest of the ring on both sides?

 

[Konstantino Nikolas]

Stupid question, but could you tell me what's attached to that carbon atom other than the CH3 and H? Do you consider it to be the rest of the ring on both sides?

Not stupid. It used to look like a maze to me before I figured out the entire thing and it became easy. Half the rest of the ring on either side.

 

[Iris Dylan Lane]

Not stupid. It used to look like a maze to me before I figured out the entire thing and it became easy. Half the rest of the ring on either side.

Isn't that going to be unsymmetrical? Three C atoms have to go on one side and two on to the other?

 

[Konstantino Nikolas]

Isn't that going to be unsymmetrical? Three C atoms have to go on one side and two on to the other?

I was kind of confused about that too. So i went the more mathematical way. Just drawing a line of symmetry. But it would be better if someone can explain it the chemistry way too.

 

[Iris Dylan Lane]

I was kind of confused about that too. So i went the more mathematical way. Just drawing a line of symmetry. But it would be better if someone can explain it the chemistry way too.

View attachment 59601

Hahah okay :') Ty for your time.

 

[Saad the Paki]

Since we're at it, why not help me with this?

 

[leenz98]

Is the answer B? ^

 

[Konstantino Nikolas]

Hahah okay :') Ty for your time.

xD np!

View attachment 59602
Since we're at it, why not help me with this?

Here you go:


The red Vs represent TWO hydrogen atoms bonded to the same Carbon atom. The red Os represent a double bond of a Carbon atom bonded to the neighboring group. So you can do this part mentally and eliminate all those Carbon atoms from the chiral list.

The yellow Os represent the chiral carbons. They are chiral because they are bonded to 4 different groups.

So the answer is C (7 chiral centres).

 

[drowning-in-studies]

How do you do Q 5 and 6?