What is Isomerism: Definition and 21 Discussions

In chemistry, isomers are molecules or polyatomic ions with identical molecular formulas — that is, same number of atoms of each element — but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers.
Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural or constitutional isomerism, in which bonds between the atoms differ; and stereoisomerism or spatial isomerism, in which the bonds are the same but the relative positions of the atoms differ.
Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues. The depth of analysis depends on the field of study or the chemical and physical properties of interest.
The English word "isomer" () is a back-formation from "isomeric", which was borrowed through German isomerisch from Swedish isomerisk; which in turn was coined from Greek ἰσόμερoς isómeros, with roots isos = "equal", méros = "part".

View More On Wikipedia.org
  1. G

    Chemistry A dilemma with stereochemistry

    The answer to this question are the ones I've marked as shown above. But I'm confused as to how? The first option is okay since it has a chiral carbon with no plane or line of symmetry and shows geometric isomerism too. In the third option, the compound shows Geometrical isomerism but i fail to...
  2. Vishesh Jain

    Chemistry Optical isomerism in spite of plane of symmetry ....?

    Shown above is an octahedral coordination complex and it's mirror image. The complex has a plane of symmetry (shown in the left diagram, a diagonal plane passing through bottom left and top right corner, perpendicular to the square plane) ... but still it's mirror image is non-superimposable ...
  3. Wrichik Basu

    Reason for Optical Isomerism (at electron level)

    I have been studying Optical Isomerism recently, and I have got one question, answer to which was not in the books that I have. I have understood what the phenomenon is, and that, how one can determine whether the plane of polarised light is rotated, and how to tell from the structure whether...
  4. H

    Ketones behaviour towards isomerism?

    In an article I read that higher ketones show metamerism because of larger substituents but still other websites reveal that they show metamerism irrespective if lower or higher? help please thanks i hope mr. borek don't find fault with it now kindly...
  5. H

    Do ketones show metamerism? If yes then how? If no then why not?

    actually my teacher told ketones don't but certain sites tel that they do...but few sites say that they dont? what's correct??
  6. AdityaDev

    Alkylation of Imines: achiral to chiral compounds

    I found this in "March's Advanced organic chemistry" After that step, on using HCl in pentane, you will get 4-methyl-3-Heptanone. So this method was used to convert achiral 2-pentanone to a chiral compound, by first converting it to the compound on left by addition reaction and then using a 2...
  7. phoenixXL

    Solving CycloHexane Isomerism: Find Total # Possible Isomers

    Question Find out the total number of possible isomers with molecular formula C6H12 that contain a cyclobutane ring. Attempted Solution In Compound 3, Optical Isomerism is possible (geometrical isomerism is also possible but is neglected due to presence of optical isomerism) about both the...
  8. N

    Is This Compound Optically Active?

    Homework Statement Is this compound optically active or inactive?? Homework Equations The Attempt at a Solution This compound doesn't have the plane of symmetry.So according to me it should be optically inactive.is it right??
  9. B

    Isomerism in coordination compounds

    Can someone outline a comprehensive way to figure out and write all the different isomers of square planar and octahedral single-centre coordination compounds, without needing to be able to see them in 3D (and without a computer)? Questions come up all the time on my exams and a proper way of...
  10. N

    [Ma4b2] Isomerism in coordinate complexes cofusion

    Consider a complex with Central Metal atom M A and B are monodentate ligands . Consider a compound with formula as [M A4 B2] . Textbook and the web says there can be only 2 possible isomers of this compound . What I say is, why can't I in the first image put A on the top and bring B...
  11. I

    Confused about E-Z Isomerism Q9) - Butane

    I know what E-Z isomerism is, but I'm confused about Q9), couldn't the answer just be all of them? FOr 10, I know its but- since there are 4 carbons in the chain but how do I know which of the options are wrong? Thanks
  12. N

    Optical Isomerism: Chirality of Compound in GMP?

    Homework Statement is this compound chiral??why or why not?? http://img827.imageshack.us/i/gmp.png/ Homework Equations The Attempt at a Solution i don't think it is...what do u think??
  13. N

    Optical Isomerism: Enantiomeric Excess Calculation from -13.9 Degrees

    Homework Statement A sample of synthetic camphor contains both the d and l isomers in unequal amounts . The specific rotation of the sample is found to be -13.9 degrees . What is the enantiomeric excess of the sample? (A) 0.215 (B) 0.314 (C) 0.417 (D) 0.167 pleasez xplain ur...
  14. C

    Cis/Trans isomerism in Alkenes

    Hey,i just need someone to check my answers :) Which of these can exist as cis/trans isomers? a.1-pentene b.2-pentene c.1-chloropropene d.3-chloropropene e.1,3,5-hexatriene f.1,2-dibromocyclodecene g.propene h.3-hexene i.2-hexene j.2-methyl-2-butene I solved it & my answers are...
  15. L

    Understanding E and Z Isomerism in 3-Isopropyl-2-Heptene

    Is this the E or Z isomer of 3-isopropyl-2-heptene? My book says Z, but I would think it's E. On the left, there is no doubt which group has higher priority. I would believe that on the right side, the lower group has the higher priority because there is a longer chain of C-atoms.
  16. K

    Reverse of optical isomerism in a reaction

    Homework Statement when chiral 2-bromobutane reacts with aqueous hydroxide ions, the optical activity of the product is reversed. Suggest why the optical isomerism is reversed. The Attempt at a Solution i have no idea... but i don't know if the fact that the hydroxide ion will attack...
  17. L

    What is the difference between structural isomerism and geometric isomerism?

    What is the difference between structural isomerism and geometric isomerism?? Yea. The thread title explains it.
  18. B

    Optical Isomerism of [Fe(H2O)6] Complex

    Hi. I'm asked the following question: What isomers does the complex [\text{Fe}(\text{H}_2\text{O})_6] give rise to? Is it optically active? My answer to the first question would be 'none': The 6 identical H2O molecules are arranged in an octahedral fashion around the central Fe-atom, so...
  19. S

    Optical Isomerism: Levorotatory Tartric Acid Reduction

    hi, if levo tartric acid was reduced to its ketone derivative would it produce exclusivly the levo form or would a racemic mix be formed or even the dextro form be formed? (any examples you give me don't have to be for tartric acid i was just using it as an example as I've been reading the...
  20. denian

    Why Does Cis-Trans Isomerism Occur?

    so, i was given a cis-isomer and a trans-isomer. the question is very simple, why this isomer shows cis-trans isomerism. i answer it this way, "because the free rotation is prevented by the presence of carbon-carbon double bond" is that a correct answer? or maybe a more valid answer?
  21. K

    Calculating Degree of Unsaturation of C4H8O - Isomerism (Chemistry)

    To draw all possible structures for C4H8O, the first step we need to do is to calculate the degree of unsaturation of the molecule. Degree of Unsatuation of C4H8O = (C+O-H)/2 = (2*4+2-8*1)/2 = 1 (meaning it has 1 double bond) [degree of C=2, H=1 and O=2] My question is why can the degree...