Draw all possible diastereoisomers of [Cr(C 2 O 4 ) 2 (H 2 O) 2 ] - . Which can exist as a pair of enantiomers?

Hi, everybody. Welcome back. Our next problem says, true or false. The given image shows all of the dia stereo isomers of and we have a complex ion here. So all within brackets with a charge two plus, we have co and in parentheses, lowercase E lowercase N subscript two. And then in parentheses, NH three subscript two with accompanying an anti American pair is clearly identified. So we have two different and anti immerse here, both showing of course, Cobalt as our central atom, we have our ligand of N, the en which is ethylene diamine, it's by dentate. So there's two of these en ligands and they're both by dentate. So they have two nitrogens that can form bonds. And then our other two ligands here are both amino groups NH three. So first, we'd put on our ligands that are by the bent take ligands. And we see we have two possible arrangements indicated here. One where we have the en ligand going from one bond within the square plane. Don't forget the octahedral arrangements have to the square plane in the middle, projecting out and projecting back from our screen and then two groups projecting up on top and bottom. So our first arrangement shows our N molecule going from one nitrogen in the square plane up to the top and then another one going from another adjoining nitrogen in the square plane down to the bottom. Our other drawing shows all of the en molecules in the same square plane. So they're both by dentate, both of them have their two nitrogens in that middle square plane. And then the NHC groups on top and bottom. So it's pretty easy to see that these are not superimposable on each other the way these are arranged, so they do not equal each other. So we definitely have at least two here. And if we try and rotate our second molecule where they're all within the square plane where this is clearly a symmetrical molecule and any rotation there will just be super imposable in the original or you can duplicate it just by rotating. However, our first molecule is a little bit different this connections on top and bottom. And what we have is a situation where we could continuously rotate this around. Now it is symmetrical. So our different rotations won't result in uns superimposable structures. So let's just put up those different rotations. And we can see that this second arrangement does have a plane of sympathy. And thus all of these different four structures I have drawn are essentially rotations of the first one. They can all be superimposed on the original structure so a little complex to think through. But again, if we focus on the fact that there's a plane of symmetry, we can each one represents a rotation around. So our given image does show all of the diary isomers, just these two versions, one with all the nitrogens in that central plane, one with them in different planes. And the pears are not labeled because since an an tumors are mirror images, we don't have any mirror images here because the first one has these sort of five rotational images. And the second one is also symmetrical. So we have no and anti American Paris. So the answer here since it's a true or false question is true because our image does show all of the dier isomers and we can't label any in anti American Paris because there are none. See you in the next video.

Ch.21 - Transition Elements and Coordination Chemistry

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McMurry 8th Edition

Ch.21 - Transition Elements and Coordination Chemistry

Problem 21.90

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Chapter 21, Problem 21.90

Draw all possible diastereoisomers of [Cr(C₂O₄)₂(H₂O)₂]^-. Which can exist as a pair of enantiomers?

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Identify the coordination geometry of the complex. Chromium(III) typically forms octahedral complexes.

Determine the ligands and their arrangement. The complex has two oxalate (C_2O_4) ligands and two water (H_2O) molecules.

Consider the possible arrangements of the ligands around the chromium center. The oxalate ligands can be either cis (adjacent) or trans (opposite) to each other.

Draw the possible isomers: For the cis arrangement, the two water molecules are adjacent, and for the trans arrangement, they are opposite.

Identify which isomers can exist as enantiomers. Only the cis isomer can have non-superimposable mirror images, making it capable of existing as a pair of enantiomers.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Diastereoisomers

Diastereoisomers are stereoisomers that are not mirror images of each other. They occur in molecules with multiple chiral centers, where at least one but not all chiral centers differ in configuration. Understanding diastereoisomers is crucial for analyzing the spatial arrangement of ligands around a central atom, particularly in coordination compounds like the one in the question.

Chirality and Enantiomers

Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, leading to the formation of enantiomers. Enantiomers are pairs of chiral molecules that are mirror images of each other and have identical physical properties except for their interaction with polarized light. Identifying which diastereoisomers can exist as enantiomers is essential for understanding the optical activity of the compound.

Coordination Chemistry

Coordination chemistry studies the structures and properties of complex compounds formed by metal ions and ligands. The geometry of these complexes, such as octahedral or tetrahedral arrangements, influences their stereochemistry and the potential for isomerism. In the context of the question, recognizing the coordination environment of chromium and the arrangement of oxalate and water ligands is vital for determining possible diastereoisomers.