Presentation on theme: "CHM 122 Wk 12, II Isomers It is possible (actually fairly common, especially in organic chemistry) for two compounds (or complexes) to have the same formula,"— Presentation transcript:
1 CHM 122Wk 12, IIIsomersIt is possible (actually fairly common, especially in organic chemistry) for two compounds (or complexes) to have the same formula, yet NOT be the same chemical substance (or species).How can you tell? At least one property is different! (You can tell operationally)How can this be? ANS: Something is different about the way the atoms in the species are “arranged”. There can be MANY ways for this to happen!Different Connections between atoms (different bonds)Same connections, but different arrangement in spaceTwo compounds (species) are called isomers if they have the same formula but are not the “same”
2 Different “ways” to be isomers (very comparable to Tro, Fig. 24.6) CHM 122Wk 12, IIDifferent “ways” to be isomers (very comparable to Tro, Fig. 24.6)StructuralOptical Isomers orCoordination IsomersGeometric Isomers cis-trans same ligand, but connected via a different atom anionic ligand swaps with counter(an)ion will occur if species is “chiral” (no plane of symmetry) other “geometrical” for salts onlyOmit in S’13
3 CHM 122Wk 12, IIExample of Linkage Isomers (a type of Structural Isomerization) *The same ligand is attached, but via a different atomCo(NH3)5(NO2)2+Co(NH3)5(ONO)2+donor atom
4 Coordination Isomers (the other kind of Structural type of isomer(s)) CHM 122Wk 12, IICoordination Isomers (the other kind of Structural type of isomer(s))The word “coordination” implies that “somebody different is coordinating” (not just a different atom, but a different ligand). [still a different “connection” or bond]How can there be a different ligand if the formula must be the same?ANS: You move a ligand “out” and put a counterion* “in”. I called this “swapping”Unlike linkage isomers (in which no counterions need be shown), one can only have coordination isomers with coordination compounds that are salts (i.e., counterions must be present/shown)*You can also swap ligands in the special case in which both the cation and anion are metal complex ions. See later
5 Coordination Isomers (continued) CHM 122Wk 12, IICoordination Isomers (continued)You can check to see if you have coordination isomers by considering the dissociation in water.When complex is dissolved in water, the complexes will have a different formula (only the “compounds” are isomers here)Remember, you cannot swap a neutral ligand with a counter anion!!!!
7 Coordination Isomers (different kind of example) CHM 122Wk 12, IICoordination Isomers (different kind of example)*As noted earlier, in the special case in which both the cation and anion are metal complexes, one can get coordination isomers by simply swapping ligands.The key is that the ligands coordinating to each metal are now different. Different “connection”[Ru(en)3][Fe(CN)6] & [Ru(en)2(CN)2][Fe(en)(CN)4]1st dissociates, get: Ru(en)33+ and Fe(CN)63-2nd dissociates, get: Ru(en)2(CN)2+ andFe(en)(CN)4-
8 Two Families of Stereoisomer CHM 122Wk 12, IITwo Families of StereoisomerIn both, all bonds are the same, but something is different about the relative positions of the atoms in spaceGeometric: not mirror imagesRelative spatial position of atoms is differentCis-trans, or other “geometric” isomerOptical (Enantiomers) : ARE mirror imagesRelative spatial position of atoms is same, except “inverted” (mirror image)
9 Example of (one kind of) Geometric Isomerism (cis-trans type) CHM 122Wk 12, IIExample of (one kind of) Geometric Isomerism (cis-trans type)All bonds same, but relative spatial arrangement differs (Cl’s 90° vs 180° degrees “apart“)
10 Cis-trans isomerization can occur in octahedral geometry also CHM 122Wk 12, IICis-trans isomerization can occur in octahedral geometry alsocistrans
11 CHM 122Wk 12, IIOrientation Needs to Be Considered! If structures are superimposable (i.e., identical), then not isomersBoth are cis (identical)Both are trans (identical)
12 Not all complexes have a geometrical isomer! CHM 122Wk 12, IINot all complexes have a geometrical isomer!
13 Yet another kind of Geometric Isomer Pair (not cis-trans)* CHM 122Wk 12, IIYet another kind of Geometric Isomer Pair (not cis-trans)*Same # and type of each bond, but different relative spatial arrangement of atoms*Tro (correctly) calls these “fac” and “mer”. You do not need to know these names, but just be able to recognize that these are geometric isomers
14 CHM 122Wk 12, IIThe following three slides are not needed for S’13, but I am including them for completeness
15 Enantiomers and “Chirality” CHM 122Wk 12, IIEnantiomers and “Chirality”A molecule or complex is chiral ifThere is NO plane of symmetryIts mirror image is NOT the same structure (i.e., NOT superimposableA molecule or complex is achiral ifThere IS one (or more) plane of symmetryIts mirror image IS the same exact structure (i.e., superimposable)Enantiomers are isomers that are mirror images, THUS:If a structure IS chiral, it WILL have an enantiomerIf a structure is achiral, it will NOT have an enantiomer
16 Enantiomers and Chirality--Examples CHM 122Wk 12, IIEnantiomers and Chirality--Examplesachiral => mirror image is identical, so no enantomerchiral => has a mirror image that is not identical