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Gauche correction in Bensen group increment

I have difficulty understanding the use of gauche correction in Bensen group increment method to calculate the heat of formation. As an example, 4 times gauche correction (0.8 kcal / mol) is ...
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1answer
19 views

Racemic mixture of meso compound

My solution manual implied that we can have a racemic mixture of a meso compound. Is this possible? I was able to rotate the molecule to make it symmetrical. Sure, the bromination in the ...
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1answer
16 views

Enantiomers or Diastereomers?

The key tells me these are enantiomers. I however don't think they are; their chiral carbons' configurations aren't inverted - i.e. only one chiral carbon's R/S configuration changes! This ...
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1answer
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Flipping a molecule vs. mirror behind compound

Why aren't these enantiomers? If you place a mirror behind the compound and look into the mirror, you get the second drawing.
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2answers
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Why is the acyclic to cyclic rearrangement of Glucose formed via the C5 hydroxyl group?

In converting glucose from its acyclic form to either cyclic form (alpha or beta) why is the C5 hydroxyl group used instead of the bottommost hydroxyl group? Also, are these structures considered ...
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3answers
54 views

R, S Configuration and Branching - Which Path?

Which path do I take when we have a branched chiral center? None of the textbooks I've consulted adequately covers this or even provides an example problem in which there was branching. Consider ...
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2answers
56 views

R,S Configuration

I don't understand why this molecule is assigned S instead of R. The H is assigned a priority of 4; the methyl group on the chiral carbon gets 3; the left carbon gets 1 and the right carbon gets ...
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2answers
56 views

What is the canonical reference for studying stereochemistry?

I am well versed with all the named reactions and all of organic chemistry. I am quite weak in stereochemistry. What canonical text can I use to study this topic and connect with other parts of the ...
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How does Walter White make pure crystal meth using a non-stereospecific reaction?

In the fantastic TV series Breaking Bad, Walter White, the dying chemistry teacher, takes to making crystal meth (d-methamphetamine) by several routes. Initially, he uses the common small-scale route ...
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178 views

Molecular chirality and optical rotation

Why does having molecular chirality result in optical rotation? The dissymetry or chirality of molecules translates to the rotation of plane polarized light, the magnitude and direction depending on ...
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1answer
628 views

Finding chiral carbons in aromatic or cyclic compounds

I know that for a carbon to be chiral four different groups should be attached to that particular carbon. But, what about in the case of cyclic compounds? What's the method to check chirality if the ...
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1answer
127 views

Racemization of biphenyl compounds

How does the effect of heat and effect of substituents affect racemization of biphenyl compounds?
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0answers
106 views

Entropy and racemization?

The process of racemization of an optically compound is entropy driven and hence nature prefers a racemic mixture to an optically active one, which is consistent with the idea of the intuitive ...
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1k views

Why is the Wittig reaction syn stereoselective?

This question is meant for a simple (not stabilized) Ylide. Consider the classical mechanism for the Wittig reaction given on Wikipedia I am not able to understand why only one intermediate has ...
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0answers
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acyclically stereocontrolled reaction: organolithium and 2-chiral compound

Aoyagi et al. (J. Am. Chem. Soc., Vol. 115, No. 24, p 11393) reported that the addition of 2-lithio-1,3-dithiane to the alpha-chiral (S)-2-Acetylpiperidine gives the (2 S,3 S)-configured product. It ...
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1answer
137 views

The Evans auxiliary: rotational freedom of the benzyl group - stereoselectivity still guaranteed?

I created the L-Phenylalanine based Evans auxiliary bearing a benzyl group with help of a molecular model set and got into some questions. The structural formula will do: As I suppose a low ...
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1answer
477 views

Effect of periodic acid on cyclohexane derivatives

Periodic acid (per-iodic acid, $\ce{HIO4}$ ) cleaves vicinal diols(to carbonyls) via a cyclic intermediate. Due to the cyclic intermediate, it needs a syn configuration for the $\ce{-OH}$ groups for ...
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2answers
1k views

How do I determine the absolute configuration experimentally?

Let's say I synthesized or isolated a chiral molecule and want to know the absolute configuration (R or S) of that molecule. I could obviously solve the structury by X-Ray crystallography, but that's ...
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2answers
5k views

How do you separate enantiomers?

There are some stereochemical reactions that result in the presence of enantiomers. When moving forward with a practical organic synthesis, how does one usually separate them in order to continue with ...