Refers to the spatial arrangement of atoms in a chemical entity.

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Boiling and melting point of trans- and cis-but-2-ene

The boiling point of trans-but-2-ene is lower than that of its cis isomer but the melting point of the former is higher than the later. Why is it not following the same order? Is there any factor of ...
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28 views

Trihalide of Nitrogen

Which is the least stable trihlide of nitrogen and why ? I have two conflicting theories , one is that Fluorine-fluorine electron repulsion will make NF3 least stable and another is steric reasons of ...
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61 views

How many stereogenic centres are there in discodermolide? [closed]

It is generally said that carbon-carbon double bonds cannot behave as stereogenic centres but the above molecule contains three such centres. Can somebody please point out all the stereogenic centres ...
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Is tetraammine dichloro cobalt (III) an optically active compound?

Is $$ \text{Co}[{(\text{N}{\text{H}}_{3})}_{4}{\text{Cl}}_{2}]$$ optically active? If so, write its stereo-isomers. I know that for a compound to be optically active, it should ...
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127 views

Are all amino acids except glycine chiral compounds?

Specifically, I was thinking of the case where the R group is a carboxylic acid functional group or an amine group. Then there would not be a chiral carbon atom. Is there a restriction on what can be ...
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Whats the H-C-H bond angle in ethene?

The carbon is $sp^2$ hybridised and is therefore planar and should also, theoretically be 120$^o$. However, VSEPR theory suggests that the pi bond would "need more space" due to greater electron ...
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422 views

Why six C atoms are usually seen in cyclic compounds?

When it gets to Carbon-based molecules, one very possible structure when there are more than six C atoms is the hexagon; though not mostly perfect, it emphasizes that six Carbon atoms tend to bond ...
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343 views

Endo rule for the Diels Alder stereoselectivity

Do you agree with the stereocenter with the CF3/CN in the product? source I would have expected that CF3 is a better electron withdrawing group than CN, and therefore placed opposite the diene and ...
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67 views

Lactone vs Ester

With regard to stereoelectronic effects in esters and corresponding s-trans lactones why does donation into the $\sigma _{CO}^*$ orbital from an anti lone pair on the sp3 oxygen cause the lactone to ...
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193 views

Why is nitration of veratrole specific in these positions?

Why do we not need $\ce{H2SO4}$ as acid catalyst for di-nitration of veratrole? Why does the 2nd nitro group go to positions 4 or 5, following the directing effects of the methoxy-group? Doesn't the ...
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190 views

“Asymmetric molecules are necessarily polar”

Is a molecule with no symmetry necessarily polar? Can a polar molecule still have some elements of symmetry (i.e. mirror image is the same as itself)? I think so ... because we can have achiral ...
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61 views

How are the Cahn-Ingold-Prelog rules applied to chiral molecules without a stereogenic carbon center? i.e biphenyls and allenes

It's easy to apply CIP rules to chiral carbons but what about in chiral molecules without these carbon cneters like biphenyls, sulphoxides and allenes? Are they applied at all?
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What is the difference between configuration and conformation in stereochemistry?

I understand conformation to be any spacial arrangement of atoms that can be achieved through rotation of a double bond. I understand conformation to be the disposition of atoms/groups in space. ...
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702 views

What is the difference between absolute and relative configuration in stereochemistry?

I am unclear as to what the difference is - It doesn't seem to explain it well anywhere. Can you help me understand the difference between absolute and relative configuration?
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45 views

Are bond angles constant?

I'd imagine the answer to the question posed in the title is no - bond angles are not constant. Covalent bonds are not infinitely rigid; hence IR as a spectroscopic technique. If so, how can we ...
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172 views

What is a dl pair in stereochemistry?

Is it two isomers with at least one stereogenic center each but the corresponding center on the other isomer will rotate the plane of polarized light in the opposite direction. Is this applicable to ...
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258 views

Are all anomers diastereomers?

I am told that all anomers are diastereomers. I think this is BS. If there is a carbohydrate with only one chiral center, then changing the configuration of the anomeric carbon gives us enantiomers. ...
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84 views

Reduction of acetaldehyde from rectus and sinister faces

I am asked to consider the reduction of acetaldehyde from the re and si faces. I am also asked whether the added hydrogen (labeled H* in my picture) is pro-R or pro-S in both cases. In my attached ...
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358 views

Concept of “non-superimposable mirror image” in chirality

I didn't understand the fact that chiral objects are non-superimposable on their mirror images. I mean, if you put your right hand (apparently an achiral object) in front of a mirror, the mirror image ...
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71 views

Si and Re facial descriptors

I am considering the hydrogenation of 2-butanone with respect to its Re and Si faces. So if we look at 2-butanone as I've drawn below from above we are looking at its rectus face. And from below we ...
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102 views

Are Grignards Chiral?

Can Grignards be chiral? I've seen them drawn as ionic structures in class. I've also seen little asterisks on certain positions of Grignards (a common designation of chirality). So this begs the ...
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237 views

Dibromomethane bond angles

With regard to the above professor's claim, I disagree. Bent's rule, which states that atomic p-character is concentrated in orbitals directed toward more electronegative substituents, implies that ...
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72 views

Bond Angles and intermolecular interactions

It's fun to consider bond angles of molecules in isolation. For example, what is the number of different bond angles exhibited by the most polar form of $\ce{SIBrClF2}$? However, can bond angles ...
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391 views

Boat conformation: axial hydrogens

In my exam, my teacher asked me if the following is true: "The chair cyclohexane has more axial hydrogens" I did not have time to think, so I just put false. And apparently I was right. But, at home, ...
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117 views

Dihedral angle of gaseous and crystalline HOOH

Why does hydrogen peroxide exhibit a dihedral angle of 111.5 degrees in the gaseous state? And a dihedral angle of 90.2 degrees in the crystalline phase? I know that in general, there is likely to ...
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385 views

Utility of Bent's Rule - What can Bent's rule explain that other qualitative considerations cannot?

Does Bent's rule have any utility? I got a vehement earful for "NO." Points raised by my professor: Coulombic considerations can be used to rationalize bond angles, strengths, and lengths without ...
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Examples of intramolecular hydrogen bonding closing bond angles

Okay, we've established that intramolecular hydrogen bonding can exist in molecules, and doesn't always serve the purpose of closing the bond angle at least relative to other stereoisomers of the same ...
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What is Bent's rule?

I'm all bent out of shape trying to figure out what Bent's rule means. I have several formulations of it, and the most common formulation is also the hardest to understand. Atomic s character ...
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414 views

Why does nitrous acid exhibit (unexpectedly) different bond angles?

Data Point 1 - quantum chemical calculations http://nzc.iap.ac.cn/uploadpdf/Wang_et_al._CSB_2007a.pdf Key points in paper: There is some sort of interaction between the hydrogen and the terminal ...
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97 views

Inversion of Configuration - Opening of Epoxide

This doesn't look like a traditional inversion of configuration: At first I dismissed the textbook author as making a typo. But then I realized that this "typo" was repeated throughout the ...
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1k views

Is this disaccharide sucrose?

I want to know if the structure I drew is sucrose or an enantiomer of it. The One I Made: The one on internet:
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61 views

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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182 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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34 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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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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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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82 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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134 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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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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272 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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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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156 views

Racemization of biphenyl compounds

How does the effect of heat and effect of substituents affect racemization of biphenyl compounds?
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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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3k 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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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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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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586 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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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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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 ...