How can the rotary power of a molecule be determined by comparing substructures?

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In summary, determining whether a molecule is dextorotatory or levorotatory cannot be done simply by looking at its 3-d presentation. It requires experimentation, specifically passing plane-polarized light through the compound. If the compound rotates the light clockwise, it is considered dextorotatory, and if it rotates the light anti-clockwise, it is considered levorotatory. There is ongoing research in this area, with some studies suggesting that the rotary power of a substructure can be applied to the entire molecule. References, such as the one published in the Journal of Organic Chemistry in 2003, can provide further information on this topic.
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louie3006
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how can i tell if a molecule is dextorotory or levorotory by looking at the 3-d presentation? any thoughts!
 
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No, we can not judge this just looking at the 3-d presentation of a compound.
It is judged by experimentation.

We pass plane-polarized light through the compound..
if the compound rotates the light clockwise, it is said to be dextro-rotatory..
and if the compound rotates the light anti-clockwise, it is said to be levo-rotatory.
 
  • #3
There is some work in that field. I remember something about the requirement to compare a part or sub structure's rotary power of a larger molecule and apply the result across the entire molecule. References within http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6THT-4CPD575-3&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1066511998&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=7b2dce750534a20105a5a375820dfe5c" (specifically, J. Org. Chem. 2003, 68, 5186) should describe one group's efforts along those lines. If you are close to a library, you might look it up.
 
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FAQ: How can the rotary power of a molecule be determined by comparing substructures?

What does dextorotory or levorotory mean?

Dextorotory and levorotory refer to the direction in which a molecule rotates polarized light. Dextorotory molecules rotate light in a clockwise direction, while levorotory molecules rotate light in a counterclockwise direction.

What causes a molecule to be dextorotory or levorotory?

The chirality, or handedness, of a molecule is what determines whether it is dextorotory or levorotory. Chirality is a property of a molecule that describes its non-superimposable mirror image. If a molecule has a chiral center, it can exist in two different forms (enantiomers) that are mirror images of each other, and one enantiomer will be dextorotory while the other will be levorotory.

How does dextorotory or levorotory affect the properties of a molecule?

Dextorotory and levorotory molecules have the same chemical and physical properties, except for the direction in which they rotate polarized light. This property is important in analytical techniques, such as polarimetry, which can be used to identify and separate enantiomers of a molecule.

Are dextorotory and levorotory molecules harmful or beneficial?

The effects of dextorotory and levorotory molecules on living organisms can vary. Some enantiomers of drugs, for example, can have different biological effects. In some cases, one enantiomer may be beneficial while the other can be harmful. This is why drug companies often produce and test both enantiomers of a drug to determine which one is more effective and safe for use.

Can a molecule change from being dextorotory to levorotory?

No, a molecule cannot change its chirality or handedness. However, some molecules can undergo a process called racemization, where they convert from one enantiomer to another. This can happen through chemical reactions or in biological systems, but the overall number of dextorotory and levorotory molecules will remain the same.

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