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

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Why doesn't every pure enantiomer racemise?

After having been acquainted with enantiomerism for nearly six months, I have one standing doubt. Consider the structure of alanine. Suppose I have a pure mixture of exclusively 'S-alanine'(left in ...
2
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0answers
21 views

Do more double bonds cause a bigger number of stereoisomers in cycloalkenes?

If trans double bonds cause cycloalkenes to be chiral, does a second trans or maybe cis double bond induce another chiral plane and hence four stereoisomer are possible for the given cyclodiene? The ...
6
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2answers
133 views

Are all higher cycloalkenes chiral?

Are all higher trans-cycloalkenes chiral as trans-cyclooctene is? This question supplements my previous question: Why is trans-cyclooctene chiral? See also the follow-on question: Do more double ...
6
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2answers
89 views

IUPAC name for 1,2,3-trichlorocyclopropane?

What is the IUPAC name for the two isomers of 1,2,3-trichlorocyclopropane? Similarly what is the name for isomers of 1,2,3,4-tetrachlorocyclobutane, 1,2,3,4,5-pentachlorocyclopentane, etc? ...
10
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1answer
313 views

Why is trans-cyclooctene chiral?

How does trans-cyclooctene exhibit chirality if there are no stereocenters? See follow-on questions: (1) Are all higher cycloalkenes chiral? (2) Do more double bonds cause a bigger number of ...
5
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2answers
47 views

Cinnamaldehyde listed as (2E)-3-phenylprop-2-enal , but is the first 2 redundant?

Wikipedia lists the molecule as being named "(2E)-3-phenylprop-2-enal", however it would appear that, as there is only 1 double bond which has a possibility of stereoisomerism, the 2 is redundant. ...
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1answer
42 views

Why are (3-methylbut-2-en-2-yl)benzene and (3-methylbut-1-en-2-yl)benzene not stereoisomeric?

My answer key says neither product exhibits stereoisomerism, but both products are substituted. Why is it that I cannot assign E/Z configuration? I thought the only time you cannot assign E/Z is ...
6
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1answer
91 views

R-S configuration considering stereoisomerism

How do I consider R-S configuration of this compound? On both the sides of carbon, the groups are same. They differ only in the relative position of hydrogen atoms. On what basis do I assign ...
4
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1answer
48 views

Reduction of butadiene with Na/NH3 - stereoselectivity

Why is the major product of the reduction of butadiene with sodium in liquid ammonia cis-2-butene (60:40) when it is thermodynamically less stable than trans-2-butene?
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1answer
30 views

How do we identify left handed and right handed crystals?

I was going through this article about how Louis Pasteur studied and explained the absence of optical activity in Racemic acid. Here's an extract: When Pasteur next examined crystals of the ...
4
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3answers
195 views

Is there a definition of rotatable bond?

Some intramolecular bonds are rotatable in the sense that the torsion angle around this bond is flexible (for example, $\psi$ and $\phi$ angles in a protein backbone). Others are essentially fixed ...
3
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49 views

Determining chirality after considering conformational interconversion in a cyclohexane

Basically I want to know what does the question mean when it says "taking into consideration conformational interconversions." I assume it means, when I draw the mirror image of the given compound, ...
1
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1answer
37 views

R configuration for cysteine

I think my prof made a mistake. Shouldn't the answer be 1, 4 and 5 instead of 2 and 3?
8
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1answer
97 views

Mark all stereocenters in ampicillin

Shouldn't the N pointed to by the red arrow also be a stereocenter? I am asking this because I think it's lone pair cannot take part in nitrogen inversion.
0
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1answer
41 views

What are all the stereoisomers of 1-ethyl-3-methylcyclohexane?

What are all the stereoisomers of 1-ethyl-3-methylcyclohexane? The following image shows my attempt to answer the question. But I am not sure if I am correct. Note: I am treating this cyclohexane ...
4
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1answer
48 views

Stereoisomers of compounds named tribromocyclobutane

Here is the link to the page in which I don't understand the answer to the last question (Question 13). The question states: Draw all of the constitutional isomers and stereoisomers of compounds ...
2
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1answer
50 views

Does the addition of base to 3-pentanone give the cis or trans enolate?

I've spent several hours searching the WWW with entries like "stereoselective enolate formation" and similar ones, but I find almost only entries for Li-amide bases (LDA, LMTP) and no other bases like ...
4
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34 views

Effect of enatiomers in pharmaceuticals

Often (or always?) one enantiomer of a certain drug will be effective and the other ineffective or harmful. The famous example is of course Thalidomide where one enantiomer caused mutilation of the ...
6
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1answer
111 views

Stereoselective enolate formation with different bases: Does the addition of a base NR3 to a ketone affords the cis or the trans enolate?

I'm wondering if the addition of a base of type $\ce{NR_3}$ (R: alkyl) to a ketone (e.g. 3-Pentanone or 4-Heptanone) results in the cis or trans-enolate. I didn't find any internet page which ...
3
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1answer
60 views

Carbohydrate conformations

I have to questions regarding the conformations of carbohydrates. There are 38 different conformations for an aldohexose or ketohexose, including $\alpha$ and $\beta$ anomers, namely 2 chairs, 6 ...
4
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0answers
23 views

Stereoselectivity of 1,3 dipolar additions

How do the 1,3 dipolar additions follow the endo rule as in the reaction below where the anti diastereoisomer is formed predominantly?
6
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72 views

Why does acetate aldol with Evans auxiliary give almost no diasteroselectivity?

Following acetate aldol gives no diasteroselectivity: Because I don't know what the basis of above statement is (I heard it in a lecture and read it on some internet web pages). I expect the two ...
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0answers
27 views

How does the stereochemistry of the enolate affect the stereochemistry of the aldol product?

Cis enolates usually produce syn aldols and trans enolates produce anti aldols. How do exemptions from this "rule" arise?
3
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0answers
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Ziegler-Natta polymerization regioselectivity

Why does the Ziegler-Natta polymerization display the regioselectivity shown in the image? Internal (coordinated to the metal) nucleophiles should attack the alkene on the less substituted end like in ...
5
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1answer
34 views

Stereochemistry of epoxide hydrolysis under acidic conditions

The epoxide on the top of the picture, in aqueous acid hydrolyzes to the compound below. What is the mechanism of this reaction? Standard epoxide opening in acidic conditions would happen at the more ...
4
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1answer
102 views

Cis-trans isomers internal energy

Whilst reading about stereochemistry, I came to know that the stability and melting point of cis isomers is lower than trans isomers. By searching on net I've found the reason behind that. But one ...
4
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2answers
73 views

Is there a formula to determine the total number of constitutional isomers?

Is there a trick or a formula that given a molecular formula, allows you to know exactly how many constitutional isomers can be formed with that many atoms? Or is it more of a trial-and-error ...
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2answers
53 views

Resolution of enantiomers? How to determine chiral compounds apart from each other? [closed]

How exactly is the interaction between two chiral compounds so they can tell the difference between S or R?
5
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1answer
195 views

Conformations of Cyclohexane

Is there any such thing as a twist chair conformation? Also, the boat and the chair conformations are achiral, while the twist boat conformation of cyclohexane is chiral and dissymetric. What about ...
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1answer
96 views

What is the difference between threo/erythro ephedrine? [closed]

I want to know how to easily make the difference or just understand the importance of stereocenters of ephedrine ?
10
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1answer
109 views

Maximum observed optical rotation through a polarimeter

Is there a maximum optical rotation of plane polarized light that can be observed using a polarimeter? I understand that in a polarimeter, light passes through a filter that converts it into plane ...
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41 views

How can the stereo selectivity in the hydrogenation of alkenes and alkynes be explained dependent on the used catalyst system?

I'm having great trouble in figuring out syn and anti hydrogenation of alkenes and alkynes. My textbooks are scattered with numerous reagents for hydrogenation but I cannot understand the ...
2
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2answers
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N(delta)-acetyl… vs N(alpha)-acetyl

Can anyone tell me what the difference between these two compounds is: N(alpha)-acetyl-ornithine N(delta)-acetyl-ornithine The only difference I can think of is the chiral properties of the ...
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What are different methods to draw/depict stereochemistry with this alkene?

The following molecule in the picture is reacting with meta -Chloropeoxybenzoic acid. My teacher flips the molecule before the reaction in such a way that only certain bonds are sticking behind or in ...
6
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2answers
207 views

Reactions between enantiomers in a racemic mixture

As a follow up to this question I started thinking about another question. During racemization, enantiomers are mixed in a equal ratios to form an optically inactive mixture. What type of reactions ...
14
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3answers
247 views

How to assign E/Z configuration according to the Cahn-Ingold-Prelog rules when subsituents differ only by stereochemistry

I stumbled-upon this compound: CC=C1C(C)CCC1(C) I'm wondering how to determine the configuration of the double bond. Is it E or Z? How do I decide on the ...
0
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0answers
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Stereoselectivity solvolysis of cyclohexenyl halides

When a functionalized cyclohexenyl halide undergoes $\ce{S_{N}1}$, does a racemic product form (due to ring flipping) ?
0
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1answer
119 views

How to calculate the number of geometrical isomers in allenes?

Can someone explain how to calculate the number of geometrical isomers in allenes like $\ce{CH3-(CH=CH)4-CH3}$ or $\ce{CH3-(CH=CH)5-CH3}$
2
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1answer
50 views

Configurations of Reactants in Second Order Nucleophilic Substitutions

The question asks me to draw the product for the reactions. However, I am stuck and do not understand how to draw the reactants with configurations correctly. (a) (S)-2-Chloropentane and NaSH I ...
6
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1answer
108 views

Planes of Symmetry and Chirality

I am trying to identify whether the following objects possess planes of symmetry or not, but my answers seem different, from the textbook solutions (Klein Organic Chemistry 2e, Page 220, Question 23). ...
5
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2answers
124 views

Why does this compound only have one pair of enantiomers?

I've been doing some reading about enantiomers, which are apparently chiral molecules that are non-superimposable mirror images of each other. An example I found of this in some problems that I've ...
3
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3answers
66 views

Chirality Centers

The compound below is fexofenadine and the only chirality center, as identified by the textbook is, the one circled in red. I do not understand why the carbon attached to the O by a double bond and ...
3
votes
3answers
96 views

Ability to Form Stereoisomers

I am asked to identify the number of stereoisomers that are possible for $\ce{H_2C=CHCH_2CH_2CH_2CH=CH_2}$ I drew the bond-line structure as follows, and I think that there can be cis and trans ...
4
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1answer
189 views

Are the circled hydrogens homotopic, enantiotopic, diastereotopic or unrelated?

I'm very confused. According to the answer key, the circled hydrogens are diastereotopic. I thought they were enantiotopic. My thought process is the following. They aren't homotopic because ...
5
votes
1answer
79 views

Torquoselectivity: Disrotatory ring opening

In organic chemistry lecture we discussed the beginning of the Woodward Hoffmann Rules with a key step of the vitamin B12 synthesis. (The initial paper from their work can be found here: ...
3
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1answer
68 views

Stereochemistry: R and S notation

How do we number the carbon atoms in symmetrical molecules while giving R and S notation. For instance, in 2,3-Dibromobutane, there is an ambiguity over which is carbon C2 and carbon C3. Will we call ...
3
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3answers
87 views

Can a meso compund be rotated in ANY sort of way in order to show its achirality?

Are there any limits to rotating a compound in order to prove that its chirality or achirality? (assuming that you're rotating about a single bond)
2
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1answer
64 views

Can pseudochirality be considered when 3 or 4 groups on the C atom are the same?

When for example the C atom is bonded to one H, and then three more structurally identical groups with 2 chiral C each - in configurations R,R and S,S and R,S respectively - then by assigning each of ...
2
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2answers
122 views

Stereochemical aspect of heating of cyclohexane-1,2-diol

Does stereochemistry play any role in the heating of Cyclohexane-1,2-diol? If I remember correctly, different products are formed depending on whether the diol is cis or trans. (I think the products ...
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Stable conformers of piperazine

which conformer stable of piperazine, when hydrogen of N in axial or in equatorial, or lone pair? why?