Skip to main content

Questions tagged [stereochemistry]

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

Filter by
Sorted by
Tagged with
99 votes
2 answers
38k views

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 ...
Dissenter's user avatar
  • 18.9k
70 votes
4 answers
28k views

How does Walter White make pure crystal meth using a non-stereospecific reaction?

In the highly-rated TV series, Breaking Bad, Walter White, a high school chemistry teacher recently diagnosed with cancer, takes to making the illicit drug, crystal meth (methamphetamine), by two main ...
matt_black's user avatar
44 votes
2 answers
108k views

How to derive these general formulae for number of stereoisomers of a compound with a possible plane of symmetry?

These formulae are used if the molecule has a possible plane of symmetry. One such example would be: Here the carbons marked with an asterisk are stereogenic centres (the asterisk is not used to mark ...
FreezingFire's user avatar
  • 1,458
34 votes
3 answers
3k views

Why is 1-ethylidene-4-methylcyclohexane chiral?

As far as I can tell, there doesn't seem to be a chiral carbon in the compound, 1-ethylidene-4-methylcyclohexane. The C-4 of the cyclohexane ring has two groups with exactly the same connectivity, and ...
orthocresol's user avatar
  • 71.5k
29 votes
3 answers
67k 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 ...
Cardtrick's user avatar
  • 965
28 votes
3 answers
2k 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: I'm wondering how to determine the configuration of the double bond. Is it E or Z? How do I decide on the priorities when the substituents can only differ in the ...
martin-is-my-name's user avatar
27 votes
2 answers
182k views

What is the difference between D and L configuration, and + and −?

What is the difference between D and L configuration, and + and −? My textbook says they are two different things. It also says that the correct way to name glucose is D(+)-glucose. Could someone ...
Mahathi Vempati's user avatar
26 votes
2 answers
31k views

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
26 votes
2 answers
12k views

What does lowercase r-s notation mean?

I came across a naming convention which I haven't seen before. I let ChemDraw name the following compound for me and got a name containing lowercase "r" and "s" configurations. Can someone tell me ...
Philipp's user avatar
  • 17.9k
25 votes
3 answers
14k views

Can heteroatoms with lone pairs be chiral centres?

If a compound has a carbon atom with four different groups covalently bonded to it, it is called asymmetric and enantiomers of the compound can exist. But imagine if one has a different central atom, ...
caconyrn's user avatar
  • 667
25 votes
1 answer
9k views

Why is trans-cyclooctene chiral?

How does trans-cyclooctene exhibit chirality if there are no stereocenters? Related follow-on questions: Are all higher cycloalkenes chiral? Do more double bonds cause a bigger number of ...
EJC's user avatar
  • 14.4k
23 votes
3 answers
16k views

Why are allenes chiral?

How is 1-bromo-3-chloropropa-1,2-diene ($\ce{BrHC=C=CHCl}$) chiral? It doesn't have any carbon that is connected to four different groups.
Rajath Radhakrishnan's user avatar
23 votes
3 answers
11k views

Why is the inversion barrier larger in PH3 than it is in NH3?

The inversion barrier in $\ce{NH3}$ is approximately $5~\mathrm{kcal~mol^{-1}}$ and that of $\ce{PH3}$ is $35~\mathrm{kcal~mol^{-1}}$. This has well-known stereochemical consequences in that amines ...
wuschi's user avatar
  • 740
23 votes
2 answers
2k views

Why don't trigonal S and P compounds undergo inversion at room temperature?

Most molecules containing nitrogen atoms in trigonal pyramid configuration undergo a relatively fast process of inversion at room temperature. On the other hand, the free energy barrier for phosphines,...
F'x's user avatar
  • 23.9k
21 votes
1 answer
7k 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 ...
stochastic13's user avatar
  • 6,795
21 votes
3 answers
3k views

What are known examples of drugs that racemize/stereoconvert in vivo, and how are they converted?

It is known that although only the (S)-enantiomer of the infamous sedative thalidomide possesses teratogenic properties, it is not very useful to administer the pure (R)-enantiomer since it is ...
user avatar
20 votes
1 answer
6k views

What are the CIP rules for cyclic substituents?

Here's what I read on Wikipedia (section "Cycles"): To handle a molecule containing one or more cycles, one must first expand it into a tree (called a hierarchical digraph by the authors) by ...
stoic-santiago's user avatar
19 votes
3 answers
3k views

Can geometrical isomers be enantiomers?

I have just been pondering upon the question above. I have found this example and I am sure they are enantiomers, but do they also count as geometrical isomers?
Harsh Katara's user avatar
18 votes
2 answers
11k 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 structure by X-Ray crystallography, but that's ...
Mad Scientist's user avatar
18 votes
1 answer
5k 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 ...
M.A.R.'s user avatar
  • 10.7k
17 votes
3 answers
5k views

Number of diastereomer pairs of 1,3-dichloro-1,2,3-triphenylpropane

How can I determine the number of possible pairs of diastereomers here? My first guess was two: RR with RS and SS with RS. But what about the potential chirality center middle carbon? There are two ...
yolo123's user avatar
  • 1,845
17 votes
3 answers
5k 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? 1,2,3-...
ℵ_ϵ's user avatar
  • 826
17 votes
1 answer
253k views

What's the difference between alpha-glucose and beta-glucose?

What's the difference between $\alpha$-D-glucose and $\beta$-D-glucose? Are they isomers? Or do they differ in their elemental composition?
a06e's user avatar
  • 729
17 votes
1 answer
4k views

Chirality of substituted adamantanes

Is this compound chiral? I can't tell where the chiral centres are because this polycyclic backbone is too confusing. I tried to draw a mirror image, but I got really confused and couldn't tell ...
orthocresol's user avatar
  • 71.5k
16 votes
2 answers
2k views

Number of stereoisomers of tetramethylspirononane

The above compound – 2,3,7,8-tetramethylspiro[4.4]nonane – clearly exhibits both optical and geometrical isomerism. The question is, how many stereoisomers does it have in all? As the number of ...
stoic-santiago's user avatar
16 votes
1 answer
413 views

Atropisomerism of naphthyl alcohol

In March's Advanced Organic Chemistry (6th ed.), it's stated that the above two are atropisomers. I don't get why is it so. How is the topmost $\ce{C}$ locked in its place? Surely, there's steric ...
user avatar
16 votes
2 answers
383 views

Is circularly polarized light ever used to isolate particular chiralities?

Chiral molecules tend to absorb one circular polarization of light more than the other. Is this ever used to isolate a particular enantiomer?
Dan's user avatar
  • 1,552
16 votes
1 answer
5k views

How are non-carbon stereogenic centers named (S/R)?

The R/S naming system for stereocenters relies on the Cahn–Ingold–Prelog priority rules to rank the four substituents of a stereocenter; the R or S name is then attributed depending on the spatial ...
F'x's user avatar
  • 23.9k
16 votes
1 answer
3k views

Neighbouring group participation with and without retention of configuration in nucleophilic substitution of 2,6-dichloro-9-thiabicyclo[3.3.1]nonane

Treatment of the dichloride A under the conditions indicated gives B with retention of configuration, while treatment of dichloride C gives D with inversion of configuration. I am having difficulty ...
justbehappy's user avatar
  • 1,799
15 votes
2 answers
8k views

Dihedral angle of gaseous and crystalline HOOH

Why does hydrogen peroxide exhibit a dihedral angle of $111.5^\circ$ in the gaseous state? And a dihedral angle of $90.2^\circ$ in the crystalline phase? I know that in general, there is likely to be ...
Dissenter's user avatar
  • 18.9k
15 votes
4 answers
2k views

Mismatch of plane of symmetry vs Gold Book's definition for a pseudochiral carbon

Here is pentane-2,3,4-triol: At first glance, without deciding the configurations at each chiral carbon, we can clearly see that this molecule has a plane of symmetry, perpendicular to the plane of ...
Gaurang Tandon's user avatar
15 votes
1 answer
5k 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 ...
Dissenter's user avatar
  • 18.9k
15 votes
2 answers
568 views

Molecular knots absolute configuration

How is the absolute configuration of chiral molecular knots determined? What rules should be applied? For centrochiral compounds, the CIP rules are applied, for axially chiral is described here and ...
EJC's user avatar
  • 14.4k
14 votes
1 answer
71k views

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 ...
Dhruba Banerjee's user avatar
14 votes
2 answers
6k views

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.
cynthia's user avatar
  • 149
14 votes
2 answers
3k views

Effect of enatiomers in pharmaceuticals [closed]

Often (or always?) one enantiomer of a certain drug will be effective and the other ineffective or harmful. The famous example is thalidomide, where one enantiomer caused mutilation of the unborn ...
RobChem's user avatar
  • 9,804
14 votes
1 answer
2k views

What are the criteria for a molecule to be chiral?

What are the criteria for a molecule to be chiral? (We frequently get questions of this type, so this is an attempt to construct a suitable general answer for duping.)
Zhe's user avatar
  • 17.5k
14 votes
1 answer
8k 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 ...
tkhanna42's user avatar
  • 2,545
14 votes
2 answers
3k views

How is the Felkin-Anh model of stereoinduction correctly explained with MO theory?

One method to predict stereoinduction in asymmetric reactions is the Felkin-Anh model (derived from the more basic Cram model) that applies to nucleophile attacks on α-chiral aldehydes. In a ...
Jan's user avatar
  • 68.3k
14 votes
1 answer
1k views

Do molecules with axial chirality have "stereogenic units"?

This question is a follow-up to a recent question on discodermolide stereochemistry that I answered here. In the course of reading IUPAC's definition of "stereogenic center", I wondered if axially ...
Curt F.'s user avatar
  • 22k
14 votes
1 answer
9k views

Does a chiral centre have to have 3 or 4 different groups attached?

I am seeing conflicting answers on the net e.g. A carbon atom is chiral if it has four different items bonded to it at the same position. (Wiki) compared to Stereocenter (chiral center): An ...
K-Feldspar's user avatar
  • 2,853
13 votes
3 answers
28k views

Difference between Epimers and Diastereomers

My lecture notes describe epimers as compounds which differ by configuration at only one carbon and gives the example of D-erythrose and D-threose as being epimers. However isn't that the same thing ...
Nanoputian's user avatar
  • 7,412
13 votes
1 answer
1k views

Is phosphorus a stereogenic centre in this phosphate ester?

My textbook says that in the above diagram that there is only 2 stereoisomers. I am guessing this is due to the stereogenic carbon atom and not due to the phosphorus atom which apparently isn't a ...
Nanoputian's user avatar
  • 7,412
13 votes
1 answer
3k views

R/S configuration of bridging carbon in bicyclic system

I am trying to figure out the R and S configuration of bridging carbons in bicyclic systems. In the image, there are two bicyclic systems and depending on the position of the Br substituent, the R or ...
QuestionCookie's user avatar
13 votes
1 answer
383 views

Can you have a meta stereocenter?

Imagine a compound such as 1,3-dibromo-1,2,3-trichloropropane. Since the first and third carbons are attached to four different groups, they are both chiral centers. Assuming that both of these ...
Niels Kornerup's user avatar
12 votes
4 answers
1k views

How is exact racemization possible? [closed]

A racemate consists of 50 % $d$ and 50 % $l$ forms of an optically active compound. But how can someone ensure exact 50% quantity comparing molecule by molecule? There will always be some difference ...
Apurvium's user avatar
  • 1,272
12 votes
3 answers
6k views

Which biphenyl is optically active?

Which biphenyl is optically active? I know that it can never be 1. I don't think it will be 4 either as I read that it should be ortho-substituted biphenyl. So, when I look at 2 and 3, I can't make ...
studious's user avatar
  • 371
12 votes
2 answers
3k views

Is it possible, chemically, to change a dextrorotatory compound to its levorotatory counterpart?

Is it possible, chemically, to change a dextrorotatory compound to its levorotatory counterpart? E.g., is it possible to change dextrodopa to levodopa?
Josh Pinto's user avatar
  • 2,461
12 votes
2 answers
2k views

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
  • 14.4k
12 votes
1 answer
4k views

Total number of stereoisomers of cyclobutane-1,2,3,4-tetracarboxylic acid

Question Find all stereoisomers of: My attempt I got four isomers, and none of them seem to be optically active as they either have a plane of symmetry or a point of symmetry: However, my sir keeps ...
ABC123's user avatar
  • 179

1
2 3 4 5
17