Optically Active /Optically Inactive

[RHONDAROBINSON]

How can I tell if a compound is optically inactive? I know the definition of optically active(able to rotate plane polarized light). Achiral molecules do not rotate plane-polarized light, but chiral molecules rotate plane-polarized light. How can I tell if they are optically active or inactive?


Rhonda

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[doc toothache]

How can I tell if a compound is optically inactive? I know the definition of optically active(able to rotate plane polarized light). Achiral molecules do not rotate plane-polarized light, but chiral molecules rotate plane-polarized light. How can I tell if they are optically active or inactive?
Rhonda

You answered your own question. Molecules that rotate plane-polarized light are optically active.

 

[RHONDAROBINSON]

Thanks for the response. I have been on Isomers in Organic Chemistry all day. How can I tell where the chiral center is in those very large molecules ?

 

[coolrunner]

look for the carbons that are attached to four different groups.

 

[NyCzPeter]

Thanks for the response. I have been on Isomers in Organic Chemistry all day. How can I tell where the chiral center is in those very large molecules ?

A chiral compound is one that contains atleast one chiral center. A chiral center is a carbon that is connected to four DIFFERENT R groups. So to find the chiral centers of a large molecule, you have to go carbon to carbon and see if all four bonds are connected to different things. Also, if the compound is chiral then it is by definition optically active, and vice versa

 

[RHONDAROBINSON]

Suppose you have 1,3-dimethylcyclohexane, where are the chiral centers? How many chiral centers are in morphine? I cannot draw these structure on this site. I do not know how.




Rhonda

 

[nanilla]

I know the definition of optically active(able to rotate plane polarized light). Achiral molecules do not rotate plane-polarized light, but chiral molecules rotate plane-polarized light. How can I tell if they are optically active or inactive?

You kind of answered your own question but their are a few things to understand about chirality and chiral centers. I would not even worry about chiral centers for these kind of questions. All chiral means is that is does not have a plane of symmetry or centers of symmetry. While achiral has one or the other.

Chiral centers dont really tell you a whole lot. An achiral molecule can have chiral centers (meso) and a chiral molecule can have no chiral centers.

As for where are the chiral centers on 1,3 ... They would be at carbons 1 and 3.

 

[doc toothache]

Suppose you have 1,3-dimethylcyclohexane, where are the chiral centers? How many chiral centers are in morphine? I cannot draw these structure on this site. I do not know how. Rhonda

1,3-dimethylcyclohexane is a mixture of cis and trans. Morphine should have chiral centers at C-5, C-6, C-9, C-13 and C-14.

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