What is Isomers: Definition and 58 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".

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  1. katsui

    I can't figure out why isomers change their structure...

    I'm new to chemistry, I'm looking at isomers, chiral topics, but I can't figure out why isomers change their structure, why chirals want to change in polarized light, why cis and trans do not remain constant but produce two different structures and which of these is the real structure, where do...
  2. I

    Chemistry Isomers of tert-butylnitrobenzene

    Question: Answer: I don't understand how the para and meta resonance structures were created (what the electron transfer was). Also, why is the ortho isomer stabilized in the same way as the para isomer? Thanks.
  3. M

    How are the isomers of tris(acetylacetonato) chromium(III)?

    Homework Statement How to draw it? Can someone tell me the electronic configuration of the chromium atom in tris( acetylaceato)chromium( III) please Homework Equations N/A The Attempt at a Solution N/A
  4. Krushnaraj Pandya

    Stability of geometrical isomers

    Homework Statement Among the following, which should be the most stable compound? 1)Cis-cyclohexane-1,2-diol 2)Trans-cyclohexane-1,2-diol 3)Cis-cyclohexane-1,3-diol 4)Trans-cyclohexane-1,3-diolHomework Equations -- The Attempt at a Solution My thought process is-cis isomers with adjacent OH...
  5. Delta2

    Caffeine Isomers and Their Effects on the Nervous System

    I noticed that different brands of espresso coffee have different effect on my nervous system. Some are really good in the sense that they wake me up and make me feel fresh and dynamic, while others do nothing, and others make me really jumpy and nervous and stressed. Why is that? I am not good...
  6. T

    Number of carboxylic acids and esters isomers for C4H8O2

    Homework Statement What is the total number of isomeric carboxylic acids and esters having the molecular formula C4H8O2? A.6 B.5 C.4 D.3 E.2 Homework EquationsThe Attempt at a Solution My answer was 4. The isomers I got was: -2-methyl propanoic acid -butanoic acid -methyl...
  7. J

    Understanding Optical Isomers: Identifying Correct Answers for Problem 1

    1. Homework Statement I thought G was the answer for part i) but it should be J, why? I can roughly see the pattern- the RHS of G is rotated 120 ° and J is formed, but why isn't G or H the answer? How to see if any two structures are optical isomers of each other? Does mirror images come into...
  8. Docscientist

    Using Iso and Neo Prefixes for Alkanes and Alkenes Isomers

    My teacher taught me to use the word "iso" and "neo" as perfix. Is it okay if I use the word "neo" for the all isomers of all the alkanes and alkenes like hexane,heptene etc.? Like for pentane we have iso pentane and neo pentane But for hexane we have names like 2,3 dimethylbutane. Is that...
  9. Anithadhruvbud

    How do I learn to make isomers for a compound?

    I get so confused when it comes to making isomers for a compound like propanol,di ethyl ketone and those which has double and triple bonds. It seems I can make an isomer by changing the position of double bonds too. Isn't there any easy way to do it? Also When I come up with 4 isomers for a...
  10. N

    Which is the more stable structure?

    Hello! I've been trying to figure out what the most stable structure of inositol is, but I keep running into conflicting information. I'm not sure whether the most stable conformation is the myo-inositol form or the scyllo-inositol. All of the stereoisomers can be seen on wikipedia at this link...
  11. J

    Possible Outcomes for Cis-Trans Isomers

    Homework Statement I chose B, because since there are 3 C=C in the compound and each C=C constituting in both cis-trans isomers. But the correct answer is C, how come there are 8? Sorry the title should be "how many cis-trans isomers"
  12. EternusVia

    Why do enantiomers rotate polarized light?

    We are currently learning about enantiomers in organic chemistry class. So far, we've covered what makes an enantiomer, the concept of chirality, optical isomer naming systems, and the physical and chemical properties of enantiomers. One of the physical properties listed is that enantiomers...
  13. Garlic

    Neutron Isomerie: Can Neutronium Have Metastable Stage?

    Hello everyone, Can a hadron be in an excited stage? If yes, can neutrons -the element- neutronium have a nuclear isomer in a metastable stage, making it have a longer half life?
  14. Prashasti

    Relative stability of ortho and para isomers

    Generally, in organic reactions, the para isomer is found to be more stable (as it is symmetrical) because of which it is produced in greater amount than the ortho isomer. However, there are some exceptions also, for example, in some reactions the less sterically hindered ortho isomer is...
  15. 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...
  16. S

    Cyclohexene radical isomers stability

    The enthalpies of creating a cyclohexene radical isomers are: ORTHO: 444 kJ/mol META: 361 kJ/mol PARA: 401 kJ/mol The meta-isomer is most stable (that is the reason for the formation of meta product in radical addition). Para/meta isomers energies seem obvious - both carbons...
  17. N

    A very simple qn on geometrical isomers

    Homework Statement Can anybody explain how this compound can have 3 geometrical isomers isomers. <----------CLICK TO SEEHomework Equations NOThe Attempt at a Solution The compound contains two double bonds hence will have 2 pairs of cis-trans isomers.That means it will have four geometrical...
  18. B

    Finding Isomers of Octahedral Complexes

    How do I find all the different geometric and optical isomers of a general octahedral complex ion with only monodentate ligands? I know well the method for finding geometric isomers in a square planar complex: any pair of ligands positioned diagonally to each other are opposite and their...
  19. E

    Geometric Isomers Lab Calculations

    Homework Statement Calculate the theoretical yield of the isomers from your data. Note: Find the limiting reagent. List of Masses I obtained during lab: Maleic Anhydride (C4H2O3): 5.05g, molar mass=98.1g/mol Impure Fumaric Acid: 2.28g Pure Fumaric Acid(trans-C4H4O4): 1.45g Pure Maleic...
  20. D

    Drawing Isomers of cyclopentane?

    Homework Statement Draw the products of the mono-chlorination reaction of methylcyclopentane. Indicate the minor and major products. Homework Equations The Attempt at a Solution I've tried looking up examples of how to do this problem but can't seem to find any. From what I...
  21. U

    Question regarding optical isomers

    Homework Statement We know that all meso compounds are optically inactive but is the reverse true? Are all optically inactive compouds meso?
  22. M

    Are cis en-en ethylenediamines always chiral in octahedral complexes?

    Hello, I am wondering... If you have two ethylenediamines (en) oriented in a cis en-en fashion, will they always have an optical isomer? I have not found a case yet where they do, and it would probably save time to assume optically active in an environment presseed for time (such as on a...
  23. Y

    Isomers of [Fe(SCN)2(H2O)4]: How Many Possibilities?

    Homework Statement How many possible isomers exist for the neutral octahedral complex[Fe(SCN)2(H2O)4]? Homework Equations The Attempt at a Solution i got three which are trans-, cis-, and the mirror image of cis-. so is there anymore? please help.
  24. M

    How many structural and cis-trans isomers are there for dichloropropene, C3 H4 Cl

    20 How many structural and cis-trans isomers are there for dichloropropene, C3H4Cl2. I could find a total of 4, with 2 structural and 2 cis trans. But the answer sheet says 7! can someone tell me all the isomers it can form?
  25. K

    How Many Isomers are in C3H6O2?

    Homework Statement How many isomers are there in the molecular formula C3H6O2? Solution: I know that the above molecular formula is propanoic acid, but it doesn't help. I wasted some time drawing structural formulas and I got 3 as the answer. Is there any short-cut way to find the answer? Thanks.
  26. C

    Identifying Possible Structural Isomers

    C3H6Br2 There are 4 structural isomers possible to draw... which I'd like to do :) The carbon skeleton isn't of much importance here, as we only have three carbon atoms. The two halides, however, are a pain, I've found. The linear sigma bonds may rotate around its axis, meaning that...
  27. D

    Are these the correct skeletal formulas for all structural isomers of C5H10?

    Homework Statement Draw the skeletal formula for all of the structural isomers of C5H10 Homework Equations The Attempt at a Solution I attached a picture of what I got so far. Are they right and am I missing any. Thanks a lot. I know that there should be another line coming from the corner...
  28. W

    Are these cis/trans isomers? Why or why

    Are these cis/trans isomers? Why or why not?
  29. C

    Enantiomers and isomers of c6h12

    alright so of the 38(as far as i know) isomers of C6H12 i have found 37/38 needing just one more,as well marks are included for enantiomers. but what I am really looking for just one more(if any) enantiomers of C6H12. what i have so far is Trans-1-ethyl-2-methylcyclopropane...
  30. S

    Isomers: Geometric and Diastereometric Isomers

    What is the difference between Diastereomers and Geometric Stereomers? Im a little confused on this one as I thought they were the same thing? Stevo1925
  31. M

    (CHEM) Which of the following compounds can exist as cis and trans isomers ?

    Using average bond enthalpy values estimate ΔH (kJ/mol) for the following gas phase r Using average bond enthalpy values estimate ΔH (kJ/mol) for the following gas phase reaction. CH2=CH2 + Br2 --> CH2BrCH2Br I followed this topic...
  32. O

    Organic Chemistry Geometric Isomers Lab

    Homework Statement The experiment was changing dimethyl maleate into dimethyl fumerate, with the intent of being analogous to changing maleic acid into fumeric acid. In the experiment, we added 1 M Bromine in dimethylchlorine to our dimethyl fumerate, put the mixture in a hot water bath and...
  33. S

    Understanding Dihydrogen Spin Isomers: An Overview and Explanation

    I am kinda rusty at my quantum, but I cannot figure out the coupling b/t ortho and para hydrogen forms. My quantum book doesn't discuss it and I really confused with the notation and superficial treatment I see on Wikipedia and other sites...
  34. E

    Gen Chem - Isomers in a complex ion

    How can you know if a complex ion has an optical isomer or not? I understand that it's when the mirror image can't be superimposed but am having trouble recognizing it. For example, take [Co(NH3)4F2]+. Does this have an optical isomer or just cis/trans?
  35. X

    Is there a systematic approach to determining isomers in organic compounds?

    Ok i don't really get how everyone forms isomers, in my class people just move carbons and other things to turn them into branches Is there a specific way to determine the isomer of a compound without guesswork and counting to c if the hydrogens and carbons stay the same? For example how...
  36. M

    Organic Chemistry- Geometric and Structural Isomers of C6H12

    Homework Statement Draw and name all of the structural isomers of hydrocarbons with the formula C6H12 (cyclohexane). 2. Relevant information This is "only" a grade 11 Chemistry Assignment, therefore I only really need the basics when it comes to isomers- not some of the more complex...
  37. C

    List & Draw Isomers of C5H10O for Chemistry Project

    I am doing an extra credit project for my Chemistry class and we have to list by name and draw the structures of as many isomers of C5H10O as we possibly can. I already have the following. 2-pentanone 3-pentanone pentanal cyclopentanol methyl isopropyl ketone 3-methyl-2-buten-1-ol oxane...
  38. S

    How many stereoisomers of C4H8Br2 have structural isomers?

    Homework Statement Name the structural isomers of C4H8Br2 and remember to number the carbon atoms such that you minimize the numbers in the name. How many stuctural isomers of C4H8Br2 are there? The Attempt at a Solution I'm not sure how many there should be. So far I've found 9...
  39. M

    Draw 4 isomers of an aldehyde C5H10O

    Hey Guys, I have a question that says to draw 4 isomers of an aldehyde C5H10O and I can only find three (pentanal, 3-methylbutanal, and 2-methylbutanal). Can anybody help with a fourth?
  40. N

    Isomers, how do you know how many to draw?

    How do I know how many isomers to draw for a molecular formula? My professor said there was a formula, but he did not know it off the top of his head. He said to google it, but I CANNOT find a formula, and I have about 12 opened windows with diff. searches *rolls eyes*. Ex. I know...
  41. A

    Are There Any Geometric or Optical Isomers in Ni(OH)2Cl(NH3)3?

    For the molecule \textrm{Ni}\left(\textrm{OH}\right)_{2}\textrm{Cl}\left(\textrm{NH}_{3}\right)_{3}, how do you determine the number of geometric and optical isomers? I first drew the molecule with a central \textrm{Cl} bonded to three \textrm{NH}_{3} molecules and a \textrm{Ni}; the...
  42. M

    Understanding Ionic Isomers in Covalent Bonded Compounds

    Im reading about covalent bonds and I read that Molecular or true formula can fully identify ionic bonding compouds but not covalent ones because they cannot identify isomers. Does that mean the only kind of compouds that can have isomers are covalently bonded compounds?
  43. L

    Isomers of Pentene So confused

    I have a question where I have to name the isomers of pentene. I understand how to do pent-1-ene and pent-2-ene, then I am stuck. Any prodding? Thanks!
  44. S

    Reason for optical activity(of optical isomers)

    Can anyone tell me the reason why an enatiomer rotates the plane of polarised light? Or at least tell me where i can read more on the reason why some compounds exibit optical activity. Thanx Saurya
  45. T

    Optical Isomers: Why Do L-Types Cost More?

    Hi all. It has been a while since I last posted. I was reading a couple of days ago about optical isomers. I found that L-type isomers cost more than D-type isomers, to manufacture and sell. I was wondering if anyone knew why? Because of the new rules on PF, I am going to state what I...
  46. A

    Isomers of C6H10 and C6H12: How Many and What Are They?

    could someone please tell me how many isomers there are for C6H10 and C6H12, even better could u tell me what they are, I was trying to get them but i keep getting too many repeats
  47. A

    Find 12 Isomers for C4H8BrCl: Get Help Here

    im trying to get the 12 isomers for C4H8BrCl, but I can only find 8, could someone please help me out ?
  48. G

    Geometric Isomers in Alkenes & Alkynes: Why?

    Hi everyone... can anyone help me out? I am not sure if i am on the rigth track. Why do geometric isomers exist in alkenes, but not in alkynes? Does it have something to do with the that alkenes have a double bond and alkynes have a triple bond? Also the pi bond restricts the rotational...
  49. S

    Isomers Of Nitrogen Difluoride

    Isomers Of DiNitrogen Difluoride.. Why Nitrigen Difluorife(N2F2) Shows Geometric Isomerism?? Can Anybody Help Me Please? Thanks!