Has isomers notes from lecture, Lecture notes of Chemistry

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V. Mozol 2023

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LO 6 Draw/recognize valid and complete Lewis diagrams, whichinclude all non-zero formal charges, and use them to draw/recognizevalid

structural isomers

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Structural (Constitutional) Isomers.^ Structural isomersare identified asthose species thathave the samenumber and type ofatoms BUT connectthem to each otherdifferently.Structural Isomerscan be identifiedusing simple Lewisdiagrams orVSEPR diagrams.^ In Chem 201 youneed to be able toboth recognizeand drawStructuralIsomers.

V. Mozol 2023

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LO 12 Draw Perspective Diagrams from valid VSEPR diagrams andvice versa, and use them to identify

stereoisomers

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Recognizing Steroisomers.^ Stereoisomers havethe same numberand type of atomsAND connect themto each other in thesame way.

How they differ is the 3Dspatial arrangementof that connection.It can be due tobond rotation or thepresence of astructural feature.VSEPR diagrams(those wherewedges and hatchesmay be present)must be used toidentifyStereoisomers.The name “stereo”implies threedimensions.

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Easiest way to “generate” one is to

rotate ONLY ONE single bond

such that

atoms change position

in space.

Questions: Could the conformational isomers A and B be represented as line drawings?

Draw a different perspective of B.

Practice finding a Constitutional Isomer CH^ CH(OH)CHCHCH^3 Convert any Lewis to a VSEPR diagram A, thenuse it to generate the conformational isomer B

A B In a first approximation most of the isomersare drawn the same way.

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CH^2

CClCH

e.g. C

HCl 3 5

To have a geometric isomer the double bond MUSThave two different groups bonded at each end. Which of the following could have geometric isomers? CHCH

CCH^3

Cl, CHClC(CH

)^32

CHClCHCH

Quick ways of finding a geometric isomer of a compound is to

exchange the two atoms/groups bonded to

to the same “end” of the double bond

and orient them differently in 3D space.

R = atom or groups of atoms.R^ and R^1

must be different from each other 2 R^ and R^3

must be different from each other 4 R^ may be the same as R^1

OR R^3 R^ may be the same as R^2

OR R^ and so on…. 3 4

Has no geometric isomers as two atoms are thesame on one side of the double bond.

Geometric Isomers – structural feature is double bond

Hint: the VSEPR diagrams for these are obtained by simply replacing the H next to the Cl in Structures A and B with a CH

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Structure A

Structure B

Constitutional isomers havedifferent condensed formulas

Structure B is ageometric isomer ofStructure A.

Z isomer (Zusammen; zame side)

E isomer (Entgegen; epposite)

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-^ Simple “optical” isomers arenon-superimposable mirror images. In this course we will concentrate on tetrahedral geometries that have four different atoms/groups bondedto them (i.e.

“chiral” centers

R -CH

CH(NH 3

)C(O)OH 2

e.g. C

HO 3 7

N 2

Quick ways of finding an optical isomer of a

chiral center (most often a carbon atom)

is to^ exchange

ANY two groups/atoms bonded to it

in 3D space. Taking a mirror image may

seem^ quicker but really

Optical isomers – structural feature is a chiral centerthink how much more of the molecule you have to make sure you draw correctly on an exam!

S -CH

CH(NH 3

)C(O)OH 2

R^ and^ S

identify the two isomers from each other. What other atoms could be chiral tetrahedral centers?

Hint: What atoms other than carbon can have four things bonded to them?

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Easiest way to “generate” one is to

exchange any two groups bonded to an

atom with four different groups

such that atoms change position in

space…but you can also take the

mirror image

.

Question:Suggest why not?

Chiral^

NOT chiral

Practice finding an Optical Isomer

optical forms cannot be isolated..side of the N atom to the other. The twoN atom and moves unrestricted from one Answer:The lone pair is in the cloud of the

drawnexactlythe same

H^ I

NBr ClN Br

Cl I

CH^ CH(OH)CHCHCH^3 A B C

Convert any Lewis to a VSEPR diagram A, thenuse it to generate the optical isomer B which is thesame as C.