Questions tagged [isomers]

Compounds that have identical molecular formula but different chemical structure.

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Reactivity of 1-bromo-4-tert-butylcyclohexane isomers with methanol

(1s,4s)-1-bromo-4-tert-butylcyclohexane (1) and (1r,4r)-1-bromo-4-tert-butylcyclohexane (2) are heated (E2) with $\ce{NaOCH3}/\ce{CH3OH}.$ Which isomer will react faster? What will change when $\ce{...
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Why does 1-ethylidene-2,3-dimethylcyclopropane exhibit cis-trans isomerism?

I think the carbons 2 and 3 have different configuration according to the CIP rules which makes the groups different: Am I correct? Is there any official criteria regarding these cases ?
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How does the size of a molecule subject to photo-isomerization affect it's isometric configuration?

When azobenzene is photo-excited to a higher energy configuration, the electron orbital take new energy levels and position's, changing the over all configuration of the molecule. Now, if various ...
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Number of stereoisomers of 1,3,5-trimethylcyclohexane

When I searched the stereoisomers of 1,3,5-trimethylcyclohexane, I got four structures given below. I don't get how structures 1 and 2, 3, and 4 are not the same. Could anyone explain?
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How can I find all possible isomers of a given molecule?

I attend a course on combinatorics (mathematics) which contains many examples related to chemistry. Unfortunately, I don't have enough chemistry knowledge to feel comfortable with the examples. For ...
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How many tetramethylcyclobutanes are possible? (structural+ geom) (no enantiomers)

I drew 5 structural isomers.(TMeCBut means tetramethyl cyclobutane) For 1,2,3,4-tetramethylcyclobutane I drew 4 geometrical isomers For ​1,2,2,3-TMeCBut I drew 2 geometrical isomers (similar to 1 ) ...
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Do ketdione molecules have diol tautomers?

In my chemistry textbook there's a keto-enol tautomerism example: But will it also be in equilibrium with pent-1,3-dien-2,4-diol in a reaction like this or will it just be a functional isomer?
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Why this structure is diastereomers instead of enantiomers

In this diagram optical isomers has divided in to 2 categories, one is diastereomers and enantiomers. Is the example for diastereomers correct? For me its looks like enantiomers
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Why doesn't 2,3-pentadiene show geometrical/cis-trans isomerism?

There are two different groups bonded to each terminal C in the C=C=C system, and there is restricted rotation about the C=C=C. So why doesn't it show cis-trans isomerism? The most common answer I get ...
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Why is the formation of the nitro isomer more favorable under acidic conditions

In the reaction between chloropenataamminecobalt and nitrite either the NO2 or the ONO linkage isomer is formed. This preference seems to be mainly due to the pH of the solution with acidic conditions ...
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Why total stereoisomers is 1 even if no geometrical isomers and optical-isomers are present [closed]

Let's for example take the complex structure type $\ce{MA_6}$, What will be the Total number of Stereo-isomers (=[Geometrical-isomers]+[optical-isomers]). My effort was that There will be no G.I and ...
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1 answer
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How many geometrical isomers will be formed here?

Can someone help me calculate the number of geometrical isomers in this compound? According to me there should be 3 isomers here but according to my teacher, there are 4.I believe that both EZ and ZE ...
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Total number of Isomers of [Co(NH3)5(NO2)](NO3)2 [closed]

I encountered this question in my country's Chemistry textbook of class 12. No solutions are published, but the answer given at the back states - "There are 10 possible isomers. (Hint: There are ...
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Does solvate isomers exist for coordination compounds with ammonia solvent as ligand?

I could find many sources confirming the hydrate isomerism(with water as solvent) but I couldn't find any information about any other solvent. In all the sources "hydrate/solvate isomerism" ...
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For a structure of a compouund optically active, what is the number of stereo isomers if no geometrical isomers are present?

Suppose for example the compounds $\ce{M(AA)3}$ and $\ce{M(AA)3bc}$, with $\ce{M}$, the central metal atom and $\ce{AA}$, a bidentate ligand. What is the total number of stereo-isomers of both? I was ...
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Number of enol forms of acetylacetone

Here is what I tried: These are the two enolic forms that I could make. So according to me, the total number of distinct enol forms of acetylacetone is $2$. But the answer is 3, what am I missing?
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What is the error in the number of aromatic isomers of C7H8O?

I am a student studying basic organic chemistry (isomerism) and was asked a question to find the number of aromatic isomers of $\ce{C7H8O}$.In fact this was a question in IITJEE exam. So I tried to ...
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The total number of stereoisomers of 1,2-dibromo-3,4-dichlorocyclobutane

I tried writing all the geometrical isomers for 1,2-dibromo-3,4-dichlorocyclobutane, and then saw if they were optical or not. And I am getting the answer as 10: However, the given answer is 8. I can'...
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Confusion in D/L nomenclature [duplicate]

With regard to carbohydrates, it is known that in a Fischer projection, if the $-OH$ group is on the right side of the lowest priority asymmetrical (chiral) carbon, then we name it as D and if it is ...
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Chirality of conformations of butane

I have read that the conformations of butane are as follows: I came across a question about number of chiral conformations of butane. My Attempt : The total or fully eclipsed is achiral because it ...
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Tautomerism between cyclohex-2-en-1-one and cyclohex-3-en-1-one

I think cyclohex-2-en-1-one and cyclohex-3-en-1-one should undergo tautomerism as shown below: I'm calling it tautomerism because of it's similarity with the tautomerism mechanism in basic medium. I ...
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Confusion in R/S Nomenclature and Chirality [closed]

I have many confusions regarding optical isomerism: What is the use of the R/S nomenclature? I understand that it is used to distinguish between the different spacial arrangements that are possible ...
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How do molecules with opposite rotational photoisomerization bonds behave? [closed]

If a molecules bond change upon isomerization with the respective bonds straining the molecules as they orient themselves opposite from each other, would the molecule undergo some kind of ...
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3 votes
1 answer
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Why is [M(AB)2] a geometrical isomer?

Our teacher told us that for coordination number 4 and tetrahedral shape $\ce{[M(AB)2]}$ doesn't have a plane of symmetry, so it shows optical isomerism. What if we take a plane passing through the ...
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What is the isomeric relation between bicyclo and spiro hydrocarbons?

Take for example octahydropentalene (bicyclo[3,3,0]octane) and spiro(3.4)octane: I would think that they are chain isomers of sort but according to nomenclature counting rules, they are both 8-carbon ...
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Isomerisation Reactions of Alkyl Halides

My organic chemistry textbook says: Haloalkanes on heating at 573K or in presence of anhydrous at low temperature undergo molecular rearrangement to form an isomeric haloalkane. I noticed a ...
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Do ambident nucleophiles form functional isomers?

I came across cyanide and isocyanide in an example for functional isomerism. As they are also ambident nuclephiles, I wanted to know if other ambident nucleophiles would also exhibit functional ...
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Does this molecule show cis-trans isomerism? [duplicate]

I want to find if the above molecule shows cis-trans isomerism, per an assignment. I am assuming that such isomerism, if present, will be shown by the substituted chlorines. It seems clear to me that ...
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How does optical activity work? [duplicate]

I have learnt that chiral molecules are able to show optical activity; that is, they are able to rotate plane polarized light by some angle. But how does it actually happen? Won't the orientation of ...
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6 votes
1 answer
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Stereoisomers of 1,3,4,6-tetramethylcyclohex-1,4-diene

How many stereoisomers are possible for following compound (1,3,4,6-tetramethylcyclohex-1,4-diene)? My Approach the 1,4 methyl groups lie in the plane, whereas 3,6 are possible chiral centers. ...
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2 votes
2 answers
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Keto-enol tautomerism in a bicyclo compound

Question Which one is more stable- the keto or enol form. The compound given is this: Solution The enol form would violate Bredt's Rule and would therefore be unstable. Hence the keto form is more ...
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4 votes
1 answer
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Assigning E–Z configuration for alkenes with cyclic substituent groups [duplicate]

I was taught that according to CIP rules, we must check the priority order for the substituents. But how can we do the same for molecules with cyclic groups as substituents? How do we compare the ...
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1 answer
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Properties of stilbene isomers

(E)-stilbene may be separated by crystallization from (Z)-stilbene and the side product of the Wittig reaction, triphenylphospine oxide (TPPO), by using absolute ethanol. My question is why? (E)-...
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2 votes
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Are (1R,2S)‐1,2‐dibromocyclopentane and (1R,3S)‐1,3‐dibromocyclopentane positional isomers?

Are these positional isomers or not? According to me they are, since Br substituent is located at different positions in both the pictures, but the answer key in one of my mock test websites says they'...
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How many stereoisomers are present in octahedral complexes of type MA3B2C?

Does $\ce{MA3B2C}$ type have optical isomerism or just geometric isomerism? I was told that it has three isomers, two cis and one trans. Are the two cis isomers optically active?
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In a pair of diastereomers, which of the following is true?

While going through my book, I came across this question and got really confused. Here's what the problem was: In a pair of diastereomers, Both can be laevo-rotatory or both can be dextro-rotatory ...
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3 votes
1 answer
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cis- and trans-isomers in equilibrium

Rotation of groups about double bonds are usually restricted due to large torsional strain and it is due to this reason that cis- and trans-isomers have their independent existence. However, certain ...
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What happens when tran-2-butene reacts with aqueous bromine in the presence of chloride?

$\ce{Br2-H2O}$, containing some $\ce{NaCl,AlCl3}$ ? I initially though that there would be anti addition of Br and OH to give 3-Bromobutan-2-ol but then I also got the intuition that NaCl might ...
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How would we arrange these in the increasing order of stability? [duplicate]

Here we have three isomers of butene there structure of who I have attached: cis-butene trans-butene iso-butene I was able to figure out that the trans isomer would obviously be more stable than the ...
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0 votes
1 answer
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Constitutional Isomers [duplicate]

Is there a formula to know how many constitutional isomers are there for a compound? For instance in this example, most students would miss the 6th constitutional isomer and will probably only write ...
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2 votes
2 answers
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Is it correct to look at plane of symmetry in substituted cyclohexane for determining a meso compound?

I read this question and it's answer by @orthocresol. Now, he has written that the compound in question is meso not because there is a plane of symmetry but because of the rapid flipping of the ...
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How many structural isomers does 1,2-dimethyl-cyclohexane have?

Can someone tell me how many structural isomers exist for 1,2-dimethyl cyclohexane? My teacher said there is one structural isomer but I believe there aren't any because there is no other way to ...
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14 votes
5 answers
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Is light a reactant in photochemical reactions?

According to IUPAC a photochemical reaction is a reaction caused by absorption of light. I still can't understand how we should consider light as a part of a reaction. Is a catalyst or a reactant? In ...
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A question about rotational symmetry of organic molecules and in particular, the cyclic Isomers of C3H4X2

I was thinking about an organic chemistry problem a few days ago but reached a dead end. There were 2 parts to this question. The first was thinking about the isomers of 'C3H4X2' [where X could be ...
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Optical activity of tartaric acid

The meso-form of tartaric acid is optically inactive due to the plane of symmetry. But how are these forms able to show optical activity when the σ-bonds can freely rotate, which can change the ...
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2 votes
2 answers
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Is reforming and isomerization the same thing?

Okay, just to give an idea of my current understanding. Reforming is a step one can do after one has cracked some hydrocarbons. As such, the process of reforming is dependent on a separate process, ...
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Number of stereoisomers of pentane‐2,3,4‐triol [duplicate]

What will be the number of stereoisomers of $\ce{CH3CH(OH)CH(OH)CH(OH)CH3}?$ By formula $2^n - 1 + 2^n + 1/2$ for $n$ being the odd number of chiral centres, it's $6;$ four optically active and two ...
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For a flat, planar molecule, how do you determine which side is up? Or down?

I was just reading about alpha and beta linkages in certain cyclic molecules, and it said that the alpha configuration was the one in which a hydrogen was sticking out above the plane, and an OH ...
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Are these molecular structures enantiomers or diastereomers?

What relationship exists between the two structures shown? I think that since the configuration at the bridge head carbons remains the same and only there is an inversion at the carbon bearing $\ce{...
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Are these molecular structures of cyclodecapentaene identical?

I think that the above structures are identical compounds as I doesn't exist in the shown form but it would exist naturally in the II form, so these should be identical. But these are mentioned to be ...
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