:''This article is about chemical isomers. For another use, see nuclear isomer''. In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of chemical bond between atoms, but in which the atoms are arranged differently. Many isomers share similar if not identical properties in most chemical contexts. A simple example of isomerism is given by propanol: it has the formula Carbon3Hydrogen8Oxygen (or Carbon3Hydrogen7Hydroxide) and the isomers Propan-1-ol (n-propyl alcohol; left) Propan-2-ol (isopropyl alcohol; right) H H H H H H | | | | | | H-C-C-C-O-H H-C-C-C-H | | | | | | H H H H O H | H Note that the position of the oxygen atom differs between the two: it is attached to an end carbon in the first isomer, and to the center carbon in the second. It can be readily shown that the number of possible isomers increases rapidly as the number of atoms increases; for example the next largest alcohol, named butane (C4H10O), has five different isomers. In the example above it should also be noted that in both isomers all the bonds are covalent bonding bonds; there is no ''type'' of bond that appears in one isomer and not in the other. Also the number of bonds is the same. From the structures of the two molecules it could be deduced that their Standard enthalpy change of formation are liable to be identical or nearly so. There is, however, another isomer of Carbon3Hydrogen8Oxygen which has significantly different properties: methyl ethyl ether: H H H | | | H-C-C-O-C-H | | | H H H Notice that unlike the top two examples, the oxygen is connected to two carbons rather than to one carbon and one hydrogen. As it lacks a Hydroxyl_group the above molecule is no longer considered an alcohol but is classified as an ether, and has chemical properties more similar to other ethers than to either of the above alcohol isomers. == History == Isomerism was first noticed in 1825, when Friedrich Woehler prepared cyanic acid and noted that although its elemental composition was identical to fulminic acid (prepared by Justus von Liebig the previous year), its properties were quite different. This finding challenged the prevailing chemical understanding of the time, which held that different chemical compound were different because they had different elemental compositions. After additional discoveries of the same sort were made, such as Woehler's 1828 discovery that urea had the same composition as, yet was not, ammonium cyanate, Berzelius introduced the term ''isomerism'' to describe the phenomenon. == Different forms of isomerism == There are two main forms of isomerism: structural isomerism and stereoisomerism. In structural isomers, the atoms and functional groups are joined together in different ways, as in the example of propyl alcohol above. This group includes ''chain isomerism'' whereby hydrocarbon chains have variable amounts of branching; ''position isomerism'' which deals with the position of a functional group on a chain; and ''functional group isomerism'' in which one functional group is split up into different ones. In stereoisomers the bond structure is the same, but the geometrical positioning of atoms and functional groups in space differs. This class includes optical isomerism where different isomers are mirror-images of each other, and geometric isomerism where functional groups at the end of a chain can be twisted in different ways. While structural isomers typically have different chemical properties, stereoisomers behave identically in most chemical reactions. Enzymes however can distinguish between different stereoisomers of a compound, and organisms often prefer one stereoisomer over the other. Some stereoisomers also differ in the way they rotate polarized light. There also exist topological isomers called topoisomers. Molecules with topoisomers include catenanes and DNA. Topoisomerase enzymes can knot DNA and thus change its topology. In nuclear physics, isomers are excited states of atomic nuclei; see nuclear isomer. ==See also== * diastereomer * enantiomer * Conformational isomerism Chemical compounds
Does the definition of "isomerism" require "the same kinds of bonds between atoms"? I would have said that, say, benzene and prismane are isomers. And is it true that "isomers typically share similar if not identical properties in most chemical contexts"? In fact the examples given in the history section seem to belie both of these claims. : User:Josh Cherry 22:18, 13 Oct 2003 (UTC) I wrote both those statements and I definitely wasn't thinking of prismane, which does seem to disprove the rule. On the other hand, I think a qualifier like "typically" or "generally" covers a multiple of ills. Since you pulled the example of prismane out of the air, I suspect you know more chemistry than me. If prismane is one of a relatively narrow category of exceptions (I don't know), then to me I think "typically" still cuts the mustard. I think the priority should be to convey information and not to construct all inclusive definitions. In other words, if rules of thumb exist, I think we should tell people. I arrived at "the same kinds of bonds between atoms" by thinking of a simple ketone or alcohol or halagonated alkane. I couldn't think of an isomer of one of those where you wouldn't still have a "C" double-bonded to "O", then I thought of the electron shell filling principle, and from there I jumped to my rule of thumb. But if you give a couple not too bizarre examples besides prismane, you'll convince me that I was mentally impaired. My motive in concocting this rule-of-thumb statement about isomers was my intuition that a reader who knows even less chemistry than I is likely to assume that there's no limit to the number of ways that a given set of atoms can bond to form a stable molecule--such that isomers (defined only as sharing the same chemical forumla) are unlikely to be more than trivially related--whereas actually something closer to the reverse is true. User:168... 00:27, 14 Oct 2003 (UTC) I don't think prismane/benzene is especially bizarre. Here are a few other isomer pairs to consider: * Cyclohexane and any acyclic hexene * Any ketone and its enol tautomer * Lactic acid and glyceraldehyde * H2C=C=CH2 and methyl acetylene * Some organic sulfate and some sulfide isomer with the oxygens put into hydroxyl groups or something User:Josh Cherry 01:44, 14 Oct 2003 (UTC) O.K.. I can't remember o-chem but I think I recognize when I see it. I just weakened the intro generalizations. Does that work for you? I think one of your examples above with a figure would be good to add somewhere below the intial one to illustrate how the intro generalizations do not always apply.User:168... 03:25, 14 Oct 2003 (UTC)
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Words begining with Isomer:
Isomer
Isomer
Isomerase
Isomerases
Isomeric
Isomeric_states
Isomeric_transition
Isomerisation
Isomerism
Isomerization
Isomers
Isomers_of_Butene
Isomers_of_butene
Isomers_of_Butylene
Isomers_of_butylene
Isomer
:''This article is about chemical isomers. For another use, see nuclear isomer''. In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of chemical bond between atoms, but in which the atoms are arranged differently. Many isomers share similar if not identical properties in most chemical contexts. A simple example of isomerism is given by propanol: it has the formula Carbon3Hydrogen8Oxygen (or Carbon3Hydrogen7Hydroxide) and the isomers Propan-1-ol (n-propyl alcohol; left) Propan-2-ol (isopropyl alcohol; right) H H H H H H | | | | | | H-C-C-C-O-H H-C-C-C-H | | | | | | H H H H O H | H Note that the position of the oxygen atom differs between the two: it is attached to an end carbon in the first isomer, and to the center carbon in the second. It can be readily shown that the number of possible isomers increases rapidly as the number of atoms increases; for example the next largest alcohol, named butane (C4H10O), has five different isomers. In the example above it should also be noted that in both isomers all the bonds are covalent bonding bonds; there is no ''type'' of bond that appears in one isomer and not in the other. Also the number of bonds is the same. From the structures of the two molecules it could be deduced that their Standard enthalpy change of formation are liable to be identical or nearly so. There is, however, another isomer of Carbon3Hydrogen8Oxygen which has significantly different properties: methyl ethyl ether: H H H | | | H-C-C-O-C-H | | | H H H Notice that unlike the top two examples, the oxygen is connected to two carbons rather than to one carbon and one hydrogen. As it lacks a Hydroxyl_group the above molecule is no longer considered an alcohol but is classified as an ether, and has chemical properties more similar to other ethers than to either of the above alcohol isomers. == History == Isomerism was first noticed in 1825, when Friedrich Woehler prepared cyanic acid and noted that although its elemental composition was identical to fulminic acid (prepared by Justus von Liebig the previous year), its properties were quite different. This finding challenged the prevailing chemical understanding of the time, which held that different chemical compound were different because they had different elemental compositions. After additional discoveries of the same sort were made, such as Woehler's 1828 discovery that urea had the same composition as, yet was not, ammonium cyanate, Berzelius introduced the term ''isomerism'' to describe the phenomenon. == Different forms of isomerism == There are two main forms of isomerism: structural isomerism and stereoisomerism. In structural isomers, the atoms and functional groups are joined together in different ways, as in the example of propyl alcohol above. This group includes ''chain isomerism'' whereby hydrocarbon chains have variable amounts of branching; ''position isomerism'' which deals with the position of a functional group on a chain; and ''functional group isomerism'' in which one functional group is split up into different ones. In stereoisomers the bond structure is the same, but the geometrical positioning of atoms and functional groups in space differs. This class includes optical isomerism where different isomers are mirror-images of each other, and geometric isomerism where functional groups at the end of a chain can be twisted in different ways. While structural isomers typically have different chemical properties, stereoisomers behave identically in most chemical reactions. Enzymes however can distinguish between different stereoisomers of a compound, and organisms often prefer one stereoisomer over the other. Some stereoisomers also differ in the way they rotate polarized light. There also exist topological isomers called topoisomers. Molecules with topoisomers include catenanes and DNA. Topoisomerase enzymes can knot DNA and thus change its topology. In nuclear physics, isomers are excited states of atomic nuclei; see nuclear isomer. ==See also== * diastereomer * enantiomer * Conformational isomerism Chemical compounds
Isomer
Does the definition of "isomerism" require "the same kinds of bonds between atoms"? I would have said that, say, benzene and prismane are isomers. And is it true that "isomers typically share similar if not identical properties in most chemical contexts"? In fact the examples given in the history section seem to belie both of these claims. : User:Josh Cherry 22:18, 13 Oct 2003 (UTC) I wrote both those statements and I definitely wasn't thinking of prismane, which does seem to disprove the rule. On the other hand, I think a qualifier like "typically" or "generally" covers a multiple of ills. Since you pulled the example of prismane out of the air, I suspect you know more chemistry than me. If prismane is one of a relatively narrow category of exceptions (I don't know), then to me I think "typically" still cuts the mustard. I think the priority should be to convey information and not to construct all inclusive definitions. In other words, if rules of thumb exist, I think we should tell people. I arrived at "the same kinds of bonds between atoms" by thinking of a simple ketone or alcohol or halagonated alkane. I couldn't think of an isomer of one of those where you wouldn't still have a "C" double-bonded to "O", then I thought of the electron shell filling principle, and from there I jumped to my rule of thumb. But if you give a couple not too bizarre examples besides prismane, you'll convince me that I was mentally impaired. My motive in concocting this rule-of-thumb statement about isomers was my intuition that a reader who knows even less chemistry than I is likely to assume that there's no limit to the number of ways that a given set of atoms can bond to form a stable molecule--such that isomers (defined only as sharing the same chemical forumla) are unlikely to be more than trivially related--whereas actually something closer to the reverse is true. User:168... 00:27, 14 Oct 2003 (UTC) I don't think prismane/benzene is especially bizarre. Here are a few other isomer pairs to consider: * Cyclohexane and any acyclic hexene * Any ketone and its enol tautomer * Lactic acid and glyceraldehyde * H2C=C=CH2 and methyl acetylene * Some organic sulfate and some sulfide isomer with the oxygens put into hydroxyl groups or something User:Josh Cherry 01:44, 14 Oct 2003 (UTC) O.K.. I can't remember o-chem but I think I recognize when I see it. I just weakened the intro generalizations. Does that work for you? I think one of your examples above with a figure would be good to add somewhere below the intial one to illustrate how the intro generalizations do not always apply.User:168... 03:25, 14 Oct 2003 (UTC)
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IA | IB | IC | ID | IE | IF | IG | IH | IJ | IK | IL | IM | IN | IO | IP | IR | IS | IT | IU | IW | IX | IY | IZ |Words begining with Isomer:
Isomer
Isomer
Isomerase
Isomerases
Isomeric
Isomeric_states
Isomeric_transition
Isomerisation
Isomerism
Isomerization
Isomers
Isomers_of_Butene
Isomers_of_butene
Isomers_of_Butylene
Isomers_of_butylene
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