26
votes
Accepted
How is exact racemization possible?
Racemization isn't "exact," but rather very very close to equality. It is just simple probability.
Think of flipping a coin, p=probability for heads, and q=probability of tails. Now for a fair flip ...
- 22.4k
17
votes
Why are conformational isomers considered as isomers?
Gaurang's answer deals well with the theory part I just wanted to give a visual aid.
(Taken from Atropisomerism of naphthyl alcohol)
Let's call the rotating substituent on the naphtahlene a fan.
The ...
- 5,532
15
votes
Why are conformational isomers considered as isomers?
I was taught that geometric (cis-trans) isomers are considered isomers because there is a high energy barrier to breaking the double bond...
There's a problem here. Geometrical isomers are isomers ...
- 9,910
14
votes
Is light a reactant in photochemical reactions?
It is neither reactant nor catalyst, and equilibrium concepts do not apply
There are processes other than photochemistry that to go in a direction away from equilibrium. They require mechanical or ...
- 42.3k
13
votes
Number of stereoisomers of tetramethylspirononane
Here is another approach to @loong's solution to the seven stereoisomers of this tetramethyl spiro[4.4.0]nonane. [This question is akin to one recently asked about tetramethylspiropentanes].
Using ...
- 17.5k
13
votes
How is plane polarized light rotated by chiral compounds?
Circularly polarized light is like a helix that twists through space. The two components are mirror images of each other.
Now, every molecule interacts with both the left-handed twisting light and the ...
- 631
12
votes
Accepted
What is the reason of the color difference for the cis/trans isomers of tetraamminedichloridocobalt(III) chloride?
If you search a library for a copy of Inorganic Chemistry by Miessler and Tarr, they have an excellent diagram showing which explains the phenomenon.
$\ce{Cl-}$ ligands have lone electrons that can ...
- 918
12
votes
Accepted
What is the error in the number of aromatic isomers of C7H8O?
You are completely correct - the furan derivatives you've drawn display unquestionable aromatic character, though the "strength" of their aromaticity is somewhat lower than various other ...
- 29.2k
11
votes
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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?
Real molecules surely do rotate around their single C-C bonds all the time(*). So yes, if two models can be superimposed after an internal rotation of such sort, this means they represent the same ...
- 31.6k
10
votes
What is the seventh plane of symmetry in benzene?
Have a look at this picture which shows some of the symmetry axes and planes. You should be able to see other similar ones. Taken from www.molecule-viewer.com.(You can also use this site to practice ...
- 31.4k
10
votes
Accepted
If a chiral molecule reacts with an achiral molecule will the product be chiral or achiral?
The key here is to look at the transition state through which the reaction proceeds.
The short answer is that the transition states are enantiomeric, i.e., also mirror images of each other, and in ...
- 17.6k
9
votes
Accepted
Number of cyclic isomers of C4H6
You can answer such questions using D.U. (Degree of unsaturation)
The formula is $\mathrm{C + 1 - }\frac{H + X - N}{2}$
...
- 640
9
votes
What is metamerism
The terms metamerism, or metamer, in a sense of chemical isomerism (there are other meanings in zoology and colorimetry), are very old. Presently, they are not used nor mentioned in authoritative ...
- 6,262
9
votes
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Stability of 4-pyridone vs 4-pyridinol
I don't think this is an either this or that situation. As with most of the equilibria we know it depends very much on the circumstances we look at it. Many examples of keto-enol-tautomerism are ...
- 44.4k
9
votes
Why doesn't 2,3-pentadiene show geometrical/cis-trans isomerism?
The (cis)/(trans) nomenclature (or, more universally applicable, (E)/(Z) nomenclature) works fine for isolated and conjugated double bonds. In the case of 2,3-pentadiene, however, where double bonds ...
- 31.4k
9
votes
How can I find all possible isomers of a given molecule?
As drawn, there are 8 positions where the OH could replace an H, but only 3 structurally unique arrangements:
Two positions: on the centre-C (above or below are a symmetric reflection).
Two positions:...
- 690
8
votes
Accepted
Why does having identical groups on either side of the pi bond lead to no geometrical isomerism?
Hmm, you seem to be having a problem visualizing the structures in the case of 2 identical groups on one carbon. But never fear, 3D molecules are here.
Check out chloroethene:
It has two identical ...
8
votes
Accepted
Reactivity of different isomers of N2F2
According to Dinitrogen Difluoride Chemistry Inorg. Chem., 2010, 49 (15), pp 6823–6833:
This increased reactivity of the cis-isomer can be readily
explained. In both $\ce{N2F2}$ isomers, each ...
- 41k
8
votes
Why are carbons of Inositol chiral centers?
Consider 2,3-butanediol.
This compound has 2 stereocenters. The meso version of this compound is achiral. However, there are still two stereo centers. As drawn, the left one is (R) and the right one ...
- 17.6k
8
votes
How is 1,4,6-trichlorodiamantane optically inactive?
From this indeed Escheresque' screen photo, I assume the following molecular structure:
which reveals to be and example of
Note: There is a nice interactive symmetry gallery at Otterbein.edu, ...
- 31.4k
8
votes
How is exact racemization possible?
It's just theory vs. real life. When mixing components, you always have limitations with the purity of chemicals and the accuracy of the balance available.
When you look at chemical reactions which ...
- 629
8
votes
Stereo-isomerism in 7-methylbicyclo[2.2.1]hept-2-ene
7-Methylbicyclo[2.2.1]hex-2-ene exists as two diastereomers, anti-1 and syn-1, which differ by the relationship of the methyl group and the double bond. Both compounds are meso with the bridgehead ...
- 17.5k
8
votes
Accepted
Assigning E–Z configuration for alkenes with cyclic substituent groups
The compound is a tetra-substituted alkene with four different groups. Thus, it could be a (E)- or (Z)-ethene. To find the priority of the groups, you must follow CIP rules. The four groups are ...
- 42.1k
8
votes
How can I find all possible isomers of a given molecule?
To do so, you need to know in advance the atoms by type (carbon, hydrogen, nitrogen, etc.), their number, and their valence. The later states how many bonds an atom may share with an adjacent atom. ...
- 31.4k
8
votes
Accepted
Geometrical isomerism in 1-(chloromethylidene)-3,5-dimethylcyclohexane
There are four stereoisomers of the compound (two pairs of enantiomers), shown in the first row.
If you swap the chlorine with the hydrogen (second row, swap from structure right above), you don't ...
- 42.3k
7
votes
What is the reason of the color difference for the cis/trans isomers of tetraamminedichloridocobalt(III) chloride?
An attempt to simplify (to make it a bit more comprehensible to a curious highschooler) and explain some of the terminologies used in Xahoc's answer. This is not intended to be a standalone answer and ...
- 4,184
7
votes
What is the reason of the color difference for the cis/trans isomers of tetraamminedichloridocobalt(III) chloride?
An easy rationalisation starts off with symmetry considerations — and indeed any rationalisation should start off with symmetry considerations. The cis and trans complexes have a notably different ...
- 68.7k
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