Questions tagged [stereochemistry]

Applicable to questions about the spatial arrangement of atoms in a molecule and how they affect its physical or chemical properties.

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Steroid nomenclature: β-sitosterol

Can someone tell me why β-sitosterol has the beta prefix? What is it denoting? When comparing its structure to other similar phytosterols I see no need for it.
waterlemon's user avatar
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Quantifying a racemic mixture by combining signal-to-noise measurements [closed]

I'm working with chromatographic data for the measurement of a chemical that takes two separable forms in equal proportions (a racemic mixture). This produces two adjacent signals (peaks) which are ...
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Tartaric acid chirality

In the image above, four variations of tartaric acid are shown: The variant in the top left is the "basic" skeletal formula of tartaric acid. The one on the top left is D-(-)-tartaric acid. The one ...
Oak Staff's user avatar
4 votes
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Is optical activity of a given compound a statistical picture?

When optical activity is taught it is done in terms of single molecules. But when it is actually measured it is done on a large collection of such molecules. So, how does the asymmetry manifest itself ...
Swaroop Chandra's user avatar
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Is this Newman projection energy profile for 2,3-dihydroxypropanal correct?

Is this Newman projection energy profile for 2,3-dihydroxypropanal correct? Also, I was to identify R/S configuration for the initial Newman projection. I am pretty sure it is R, but I need help here ...
Bee's user avatar
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Chirality of 1-Pentanol and 3-Methyl-2-Pentanol

Q) Which of the following is chiral? a) 1-Pentanol b) 3-Pentanol c) 3-Methyl-2-butanol d) 3-Methyl-1-butanol Answer: c) If structure and it's mirror image are not superimposable then it's ...
user406653's user avatar
5 votes
1 answer
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How to draw Fischer projections for carbon chain having more than two carbons?

How can we draw Fischer projections for one-five carbon compounds? For example, say we have pentane-2,3,4-triol ($\ce{CH3-CHOH-CHOH-CHOH-CH3}$; image below). With wedge and dash structure, the ...
Matt's user avatar
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4 answers
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Are our hands really chiral?

Everyone says that our left and right hand are mirror images of each other and are non-superimposable, unlike a sphere whose mirror image is exactly superimposable. But shouldn't our left and right ...
Matt's user avatar
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1 answer
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Why isn't Cahn Ingold Prelog principle used to name the isomers of complex compound having square planar geometry & different ligands attached to it?

For a complex compound with coordination number 4, say having square planar geometry, and say all the ligands attached to the central metal atom are different, then we know that we will get 3 ...
Yb609's user avatar
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7 votes
4 answers
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Racemic mixture or not?

Will the following reaction give a racemic mixture or not? According to me, it should give. But my teacher disagrees, but I cannot understand the reasons he gave. Shouldn't there be equal approaches ...
MrObjectOriented's user avatar
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The reaction which forms a pair of diastereomers

The reactions among the following which results in the formation of a pair of diastereomers are: I am aware of the fact that $\ce{HBr}$ gives anti addition product and $\ce{BH3}$ forms syn addition ...
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Predicting the product of a hydrogenation reaction

The question is to predict the nature of the product(s) of the above reaction, that is if the product(s) form a racemic mixture, meso, diasteromers, or are structural isomers. I am aware of the fact ...
Pink's user avatar
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[3+1]-Cycloadditions of Sulfur Ylides and 1,3-Dipoles(?)

My question is basically regarding the stereoselectivity of the situation. I am not being able to decide on the positioning of the sulfur ylide with proper justification. In the attached hand-drawn ...
Eashaan Godbole's user avatar
2 votes
2 answers
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Configuration change at chiral carbon in SN2 reaction

Consider $\ce{A}=\ce{CH(CH3)(C2H5)(C3H7)}$ in R configuration. Suppose somehow in a $\mathrm{S_N2}$ reaction, $\ce{Br-}$ attacks and replaces $\ce{-H}$ (this compound we call $\ce{C}$). Now we expect ...
RandomStudent's user avatar
14 votes
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Configuration of chiral center in cocaine

I couldn't get the absolute configuration for the chiral center I marked. I got R, but according to my answer key it is apparently S. Would really appreciate an explanation.
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How do I determine stereochemistry of the product [closed]

When pure (L) lactic acid is esterified by racemic-2 butanol then what is the nature of the stereoisomers so obtained i.e. whether they are diastereomers or enantiomers. I studied the mechanism of ...
Pink's user avatar
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How to determine the stereochemistry after elimination of anti-1-bromo-2-methylcyclohexane?

The question is asking for the product and the answer is C. My expected answer was E. Here's how I tried to solve it: Since Br (the leaving group) is at the equatorial position, the structure would '...
Cindy's user avatar
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Halogenation of alkenyl boranes

When a terminal alkenyl borane is succumbed to halogenation where the halogen and the base are added in two separate steps, the geometry of the double bond is changed. When they are added ...
EJC's user avatar
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How to determine which reagent to use H2; lindlar catalyst vs Na;NH3(l)?

I do understand that H2; Lindlar will give a cis double bond and Na;NH3(l) will give trans double bond. However, I am having difficulty understand how to determine which reagent will work in this ...
oneCoderToRuleThemAll's user avatar
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When is rotation around double bonds to form cis-trans isomers allowed?

Textbook Question: The rhodopsin molecules in the retina contain a derivative of vitamin A called cis-retinal (Figure 6). On exposure to light, cis-retinal becomes an isomer called trans-retinal. ...
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For molecules to be enantiomers, do the groups have to be non-superimposable mirror images even when rotated around C-C single bonds?

For example, if I rotate the Carbon-Carbon bond in B around 120 degree anti-clockwise, I would get the molecule shown in image C. C looks to me like a non-superimposable mirror image of A, hence A and ...
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For molecules to be enantiomers, do their bonds have to point the same way?

Enantiomers are non superimposable mirror images. What is bothering me is: If the bonds point different ways are they still considered superimposable and hence enantiomers? To illustrate, comparing X ...
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How to differentiate diastereotopic protons by NMR in flexible groups?

In (1⁠R,2⁠S)-2-(hydroxymethyl)cyclohexan-1-ol shown below, Ha and Hb are diastereotopic (they will have different chemical shifts), but because of fast rotation, NOESY should show that both couple ...
EJC's user avatar
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What's the exact difference between (-)-BTX and (+)-BTX

I quite liked this article, which describes the synthesis of (-)-batrachotoxin as well as a steroisomer, (+)-batrachotoxin. I would like to know what the precise difference is between the two: are ...
Emilio Pisanty's user avatar
3 votes
1 answer
7k views

Defining a stereospecific reaction

My textbook says that a reaction which gives different stereoisomeric products when the different stereoisomers of starting material are used in a stereospecific reaction. Is it necessary that all ...
Pyro Recorcinol's user avatar
5 votes
1 answer
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Determination of (R) and (S) configurations from a Haworth projection

Short version of question : How do I know which groups are equivalent to "out of and into the page (like in the Fisher projection)" for the Haworth projection (so that I can send the lowest priority ...
K-Feldspar's user avatar
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2 votes
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Best chair configuration for trimethylcyclohexane matching a specific Haworth projection?

Which option best depicts trimethylcyclohexane shown in the Haworth projection below? I thought B because All the methyl groups are equatorial and equatorial groups are more stable. All the methyl ...
K-Feldspar's user avatar
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7 votes
1 answer
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E/Z configuration of the central double bond in a highly branched poly-ene

What would be the configuration of the marked double bond in the attached molecule?
EJC's user avatar
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Diastereoselective epoxidation of acyclic alkenes with VO(acac)2

I've been reading about diastereoselective epoxidation of acyclic alkenes with VO(acac)2. This is taken from Carey, Sundberg Advanced Organic Chemistry Part B: The OH and epoxide are syn. Then, while ...
EJC's user avatar
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12 votes
2 answers
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Sulfinate R/S configuration

How to determine the configuration of the attached chiral compound? It can be represented with two Lewis structures, in the one to the left, the =O substituent has the biggest priority, while in the ...
EJC's user avatar
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4 votes
1 answer
757 views

Are alkenes with bulky groups attached (like the one shown in the picture) chiral or achiral?

Is the compound in the picture chiral or achiral? I think it should be achiral for the following reasons: There is free rotation. I know, but for every configuration produced by free rotation ...
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1 vote
1 answer
3k views

Correct way of drawing D-configuration with this stereochemistry?

Hello! I have completely memorized how to draw all 20 amino acids in the way seen in the picture (middle, between the "ball-and-stick" and fisher projection) By my understanding this is in the L ...
Johan's user avatar
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2 votes
2 answers
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For isomers, what does the term "connectivity" mean?

I would like an explanation for the term "connectivity" in the question "Do the compounds have the same connectivity? I do not understand what "connectivity", a vague term, means.
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2 answers
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Why was the definition of chiral carbon changed?

Before 1984, the definition of chiral carbon was, carbon atom that is attached to four different types of atoms or groups of atoms In 1984, the definition was changed to Any carbon molecule ...
Vedant's user avatar
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26 votes
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Is cis-1,2-dimethylcyclohexane a meso compound?

I was watching a video lecture today on hydrocarbons and came across this. The instructor says that, as there is a plane of symmetry, cis-1,2-dimethylcyclohexane is a meso-compound: However, the ...
user avatar
5 votes
2 answers
840 views

Does bicyclo[3.2.0]heptane have a plane of symmetry?

Most stable form of cyclobutane is the "envelope form" and most stable conformation of cyclopentane is either the "envelope form" or the "twist" form. In the above compound do the individual ...
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0 votes
1 answer
382 views

Stereochemistry of cycloalkanes having substituents

My teacher said that from $3$ to $6$ member cycloalkanes having any number and type of substituents we can always draw the planar structure and decide the specifics of stereochemistry like: ...
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1 vote
1 answer
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Can the following compound having a centre of symmetry be called both optically inactive and meso?

The Centre Of Symmetry (COS) has been shown by a blue dot. My questions are: Can this molecule be called optically inactive? I have this doubt because single bonds permit free rotation and the ...
user avatar
2 votes
1 answer
514 views

Can the following molecules be called meso compounds (cyclic structures which usually exist in non-planar forms)?

In the planar form the following molecules have one plane of symmetry.However in the chair-form (the most stable form) for the first molecule and the non-planar form for the second molecule there is ...
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10 votes
2 answers
3k views

Does trans-decalin really have a plane of symmetry?

My teacher told me that trans-decalin (see below) is achiral due to the presence of both, a centre of symmetry and a plane of symmetry. But I could not spot the plane of symmetry untill now. Can ...
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2 votes
1 answer
564 views

Assigning Re and Si face for Carboxylic group

Suppose I have a compound $\ce{CH3COOH}$ and I have to assign Re and Si faces. Which of the two oxygens get a higher priority and why?
TESLA____'s user avatar
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1 answer
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Is it possible to generalize whether an organic molecule is chiral or not?

Can we generalize on the basis of number of chirality centers if an organic molecule is chiral or not?
Pyro Recorcinol's user avatar
1 vote
0 answers
42 views

Are Meso compounds isomers? [duplicate]

According to my chemistry manual meso forms are "a particular case of of stereoisomers" implying that they are isomers, anyway right after this sentence the manual states that if you rotate the 2 ...
Mirko's user avatar
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1 vote
2 answers
8k views

How many carbons does an alkane need to have an enantiomer?

How many carbon atoms does an alkane need before it is capable of existing in enantiomeric forms?
Nilay Mohod's user avatar
1 vote
2 answers
624 views

R & S Stereochemistry of an unsaturated ring system

Using the R- & S- nomenclature assign a configurational symbol to decalin 4-methyl (above the plane), 4-hydroxy (below the plane), 7-isopropyl (above the plane), 1,9 diene. (Numbering the carbons ...
tony's user avatar
  • 347
-2 votes
1 answer
14k views

What are two superimposable mirror images called? [closed]

I know that enantiomers are mirror images which are not superimposable on each other. What about mirror images which are superimposable? Are they necessarily the same molecule? Is there a particular ...
Victor M's user avatar
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5 votes
2 answers
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Why is the cis isomer of 1,3-dimethylcyclobutane more stable than the trans isomer?

I expect there to be more steric repulsions between the two methyl groups if they are on the same face as each other. Why is this not the case?
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3 votes
2 answers
1k views

Why is the value of specific rotation different in different cases?

An unknown compound with a mass of $4.5~\mathrm{g}$ is dissolved in enough carbon tetrachloride to make a total volume of $250~\mathrm{cm^3}$. The observed rotation of this solution is $+357.75^\circ$...
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2 votes
1 answer
397 views

How many alkanes having a molecular weight of hundred, are chiral?

I successfully found 2, but the answer key says that there are 4 such compounds possible. I found: 3-methyl hexane 2,3-dimethyl pentane We can't have a cyclic ring as the masses won't match. What ...
Prakhar's user avatar
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5 votes
1 answer
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What is the percentage of d-tartaric acid in a mixture of d and l isomers?

Specific rotation for pure tartaric acid is $-12 ^\circ$. A mixture of d-l isomers is prepared which has a specific rotation of $+6^\circ$. What is the percentage of d-tartaric acid in a mixture of $d$...
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