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Why is cis-1,2-dichloroethene more stable than trans-1,2-dichloroethene?

Here's a pre-MOT rationalisation of the cis form being more stable than the trans form for 1,2-dihaloethylenes: The lone pair of chlorine atoms is involved in resonance with the double bond, as it ...
Archer's user avatar
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13 votes

How to check for geometrical isomerism in cyclic compounds?

I hope the statutes of limitation haven't run out. Structure 1 is a (Z)-alkene. Using Cahn-Ingold-Prelog (CIP) protocol, the rings are deconstructed as shown in diagram 2. The larger red arrow marks ...
user55119's user avatar
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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 ...
user55119's user avatar
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13 votes
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Can geometrical isomers be enantiomers?

The enantiomers 1a and 1b can have their double bonds defined by CIP rules 1a and 5. Rule 1a dictates that CH3>H while Rule 5 has R>S. Thus, 1a has an E-double bond and 1b is of the Z-...
user55119's user avatar
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12 votes
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The number of geometrical isomers of complex of type [Ma₃b₂c]

First, let's establish that we're all talking about octahedral complexes to eliminate any possible confusion. Fix $\ce{c}$. You can have either $\ce{b}$ trans or $\ce{a}$ trans. If $\ce{b}$ is trans ...
Zhe's user avatar
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12 votes

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

I managed to crack the formula for optical isomers with odd chiral centers, so I'll share my attempt here. Hopefully others may innovate on it and post solutions for other formulae. Pseudo-chiral ...
Gaurang Tandon's user avatar
12 votes

Can geometrical isomers be enantiomers?

Technically, this double bond should not be labelled as (E)- or (Z)-. It is what is known as an enantiomorphic double bond, for which the proper stereodescriptors are seqCis and seqTrans. This is ...
orthocresol's user avatar
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12 votes
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Does 1,4-dimethylcyclohexane have a chiral center?

As it is said in the definition of IUPAC, for a carbon atom to be chiral it should be attached to 4 different groups: In case of 1,4-dimethylcyclohexane, you will see that the two groups on the right ...
Azamat's user avatar
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11 votes

Determining if the product would be cis or trans after an anti elimination on fischer projections

As you have mentioned, the basic Fischer operations are: Vertical positions are below the plane of paper and horizontal positions are Above the plane of paper, thus you have already remember that when ...
Mathew Mahindaratne's user avatar
10 votes

Why is cis-1,2-dichloroethene more stable than trans-1,2-dichloroethene?

In this answer, I will point out an inadequacy of the reasoning based on resonance structures and I will also provided another MO perspective, which I believe is more convincing, on the issue. A ...
Tan Yong Boon's user avatar
10 votes

Can geometrical isomers be enantiomers?

Edited version: I originally wrongfully assumed these two structures are not geometrical isomers of the double bond, because it is a trisubstituted double bond with at least two identical groups (...
Mathew Mahindaratne's user avatar
10 votes
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Determining if the product would be cis or trans after an anti elimination on fischer projections

There are two possible eliminations that can happen (see the image below) As you can see, we then have two final products depending upon which $\ce{H}$ is eliminated. From the image 1a is cis and 2a ...
Safdar Faisal's user avatar
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 ...
Buttonwood's user avatar
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8 votes
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Determining geometry of trisubstituted alkene

As @Zhe points out, its not possibly to definitively answer your questions without knowing the structure of the olefin, as its important what is around the olefin, as well as just how many protons are ...
NotEvans.'s user avatar
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8 votes
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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 ...
Pritt says Reinstate Monica's user avatar
7 votes
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E/Z stereoisomers : assigning priorities with a cycloalkane group

The reasoning you have used is clearly faulty as there is no meaning in assigning more number of carbon to one end in a cyclic system. Just look at the both the branches you have marked using orange ...
Pulkit Aditya's user avatar
7 votes

Number of geometrical isomers when a cyclic ring is involved along with axis of symmetry

The answer in your textbook is correct. Here are all possible isomers: I added a symmetry axis to the right, so you can see that these compounds are mirror images and are not superimposable. The ...
vapid's user avatar
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7 votes

How to determine if an alkene is an E or Z isomer?

Just adding on to Ivan's comment, you have to split the double bond "into half" such that both halves have two sets of double bonds not having "to split and remain with single bond". After that ...
xavier_fakerat's user avatar
7 votes

Number of Stereoisomers of C(CHClCH3)4

To answer your question, if you haven't figured it out by now, RRSS is the same as RSRS and it is the only one of the five that is optically inactive (Compare with nonactin). Structure A numbers the ...
user55119's user avatar
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7 votes
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Stereoisomers of 1,3,4,6-tetramethylcyclohex-1,4-diene

Your compound, 1,3,4,6-tetramethylcyclohex-1,4-diene, does not have line symmetry (plane of symmetry), and hence $\ce{C}$3 and $\ce{C}$6 are chiral centers. Thus, maximum possible stereoisomers are $2^...
Mathew Mahindaratne's user avatar
6 votes

Why is this molecule considered a cis isomer of 2-bromobut-2-ene?

With the same reasoning as provided here, I recommend that you name this compound (2 E)-2-bromobut-2-ene. Using (cis/trans) may be useful around an isolated double bond with only two substitutents. ...
Buttonwood's user avatar
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6 votes

Are glucose and galactose cis-trans isomers of each other?

Glucose and Galactose are best described as epimers of one another. The three structures below all have the same molecular formula and the same connectivity, but differ in the absolute configuration ...
NotEvans.'s user avatar
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6 votes

How many stereoisomers are possible for 1,2-dimethyl-4-(propan-2-ylidene)cyclopentane?

In this structure the left hand methyl groups can be on the same side of the ring. This is one stereoisomer. This molecule is not chiral and there is only one isomer with the methyl groups on the same ...
matt_black's user avatar
6 votes

Is there geometrical isomerism in case of 2-methylcyclopentanone?

If you look at the structure of 2-methylcyclopentanone, you'll notice that it is asymmetric about the C-2 atom This gives rise to two isomers; the R isomer on the left and the S isomer on the right ...
Aniruddha Deb's user avatar
5 votes
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Are glucose and galactose cis-trans isomers of each other?

Since the question was revised, I have revised the answer as well to include more information: Part A Glucose and galactose are not cis isomers, but diastereomers called epimers, Two sugars that ...
xavier_fakerat's user avatar
5 votes
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When is rotation around double bonds to form cis-trans isomers allowed?

Generally, all single bonds are said to permit free rotation while all double bonds are said to inhibit free rotation. This can actually be explained numerically as well: the rotation around the $\ce{...
Jan's user avatar
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5 votes

When is rotation around double bonds to form cis-trans isomers allowed?

In rhodopsin this normally occurs only after the 11 cis in the chromophore (a retinylidene schiff base) is placed into an electronically excited singlet state after absorbing a visible photon. This ...
porphyrin's user avatar
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5 votes

Why is tautomers not possible in benzoquinone?

You could sort of devise a tautomer by transferring an $\alpha$ hydrogen from carbon to oxygen. But if you draw the resulting structure you find a pair of cumulated double bonds. That tends to be ...
Oscar Lanzi's user avatar
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5 votes

Does CHT=CHT have a geometric isomerism because of tritium atoms?

Yes isotopes can induce geometric isomerism. You can induce chirality by using different isotopes of atoms; the molecule $\ce{CHDClF}$ is chiral with the deuterium atom (you do not need radioactivity)...
Oscar Lanzi's user avatar
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