IB Chemistry on Structural Isomers, Geometric Isomers and Stereoisomerism

http://lawrencekok.blogspot.com

Prepared by Lawrence Kok

Tutorial on Structural Isomers, Geometric Isomers and Stereoisomerisms.

http://lawrencekok.blogspot.com/


Isomerism

Isomers – Organic molecules with same molecular formula but different arrangement of atoms

Two types of Isomerism

Structural Isomerism• Same molecular formula• Different structural formula• Different arrangement of atoms

Stereoisomerism• Same molecular formula• Same structural formula• Different spatial arrangement of atoms

Isomerism


Two types of Isomerism

Structural Isomerism• Same molecular formula• Different structural formula• Different arrangement of atoms

Hydrocarbon Chain Isomer• Different hydrocarbon chain skeleton

Stereoisomerism• Same molecular formula• Same structural formula• Different spatial arrangement of atoms

Positional Chain Isomer• Different

functional group position

Functional Group Isomer• Different functional group

Geometric Isomers

Optical Isomers

Cis IsomersAtoms are located

on the same side

Trans IsomersAtoms are located

on the different side

CH3 -CH –CH2 –CH3

│ OH

CH3 -CH –CH –CH3 │ OH

CH3 –CH2–CH2 – O – CH3


Structural Isomerism

Structural Isomerism for C4H9OH• Same molecular formula• Different structural formula• Different arrangement of atoms


Positional Chain Isomer• Different functional group position


CH3 –CH2 –CH2 –CH3

│ OH


│ OH

Butan – 1-ol

Butan – 1-ol

Butan – 1-ol



│ OH



Structural Isomerism for C4H9OH• Same molecular formula• Different structural formula• Different arrangement of atoms


Positional Chain Isomer• Different functional group position



│ OH

CH3 –CH2 –CH –CH3 │ OH

CH3 - CH – CH2 – OH │ CH3

CH3 │ CH3 - C – OH │ CH3


│ OH

CH3 –CH2–CH2 – O – CH3

CH3 –CH2 – O – CH2 -CH3

Butan – 1-ol 2- Methylpropan-1-ol

2- Methylpropan-2-ol

Butan – 1-ol Butan – 2- ol

Butan – 1-olMethoxypropane Ethoxyethane



│ OH

H │CH3 –CH2– C=O

Structural Isomers for C4H9OH – All have same Molecular Formula but different Structural Formula




│ OH

C4H9OH

Structural Isomers for C4H9Br – All have same Molecular Formula but different Structural Formula


│ Br

Structural Isomers for C3H6O – All have same Molecular Formula but different Structural Formula

C4H9Br

C3H6O

H │CH3 –CH2– C=O

O ║ CH3 – C– CH3

Structural Isomers for C4H9OH – All have same Molecular Formula but different Structural Formula




│ OH

CH3 –CH2 –CH –CH3 │ OH

CH3 - CH – CH2 – OH │ CH3

CH3 │ CH3 - C – OH │ CH3

CH3 –CH2–CH2 –O – CH3

CH3 –CH2 –O– CH2 -CH3

C4H9OH C4H9OHC4H9OH

C4H9OH

C4H9OH C4H9OH

Structural Isomers for C4H9Br – All have same Molecular Formula but different Structural Formula


│ Br

CH3 –CH2 –CH –CH3 │ Br

CH3 - CH – CH2 – Br │ CH3

CH3 │ CH3 - C – Br │ CH3 Structural Isomers for C3H6O – All have same Molecular Formula but different Structural Formula

OH │CH3 –CH = C-H

OH │CH2 =CH - C-H2

CH3 – O – CH = CH2

C4H9Br C4H9Br C4H9Br

C4H9Br

C3H6O C3H6O C3H6O C3H6OC3H6O

Geometrical Isomerism

Geometric Stereoisomerism• Same molecular formula• Same structural formula• Different spatial arrangement

of atoms

Requirement for geometrical isomers• Presence of C=C double bond to prevent bond rotation• Presence of ring structure to prevent bond rotation• Carbon atom in double bond must be bonded to different atoms

Cis IsomersAtoms are located on the same side

Trans IsomersAtoms are located on the different side



of atoms




Presence of Double Bond C=CCI –CH=CH –CI

CI CI │ │ C = C │ │ H H

CI H │ │ C = C │ │ H CI

Cis 1, 2 dichloroethene

Trans 1, 2 dichloroethene



of atoms





CI CI │ │ C = C │ │ H H

CI H │ │ C = C │ │ H CI

Presence of ring structure


Trans 1, 2 dichloroethene Cis

1, 2 dichlorocyclopropaneTrans

1, 2 dichlorocyclopropane


Geometric Isomers• Same chemical properties – Same functional group• Different physical properties – Different spatial arrangement (Different density, polarity, solubility, melting point /boiling point)


of atoms





CI CI │ │ C = C │ │ H H

CI H │ │ C = C │ │ H CI

Presence of ring structure


Trans 1, 2 dichloroethene Cis

1, 2 dichlorocyclopropaneTrans

1, 2 dichlorocyclopropane

Carbon atom bonded to different atoms

H CI │ │ C = C │ │ H H

H CI │ │ C = C │ │ H H

CI CI │ │ C = C │ │ H H

CI H │ │ C = C │ │ H CI

NO Cis/TransCis

1, 2 dichloroetheneTrans

1, 2 dichloroethene

X X

Geometric IsomerismGeometric Isomers – Organic molecules with same molecular/structural formula but different spatial arrangement



CI –CH=CH –CI CI CI │ │ C = C │ │ H H

CI H │ │ C = C │ │ H CI

Cis 1, 2 dichloroethenem/p : -80C ↓

Trans 1, 2 dichloroethenem/p : -50C ↑

CH2 –CH = CH–CH2 CH3 CH3 │ │ C = C │ │ H H

CH3 H

│ │ C = C │ │ H CH3

Cis but-2-enem/p : -139C ↓

Trans but-2-enem/p: -106C ↑

Cis melting point is lower ↓ Trans melting point higher ↑

Cis

Isom

er

Trans

Isomer


of atoms





CI H │ │ C = C │ │ H CI

Cis 1, 2 dichloroethenem/p : -80C ↓

Trans 1, 2 dichloroethenem/p : -50C ↑

CH2 –CH = CH–CH2 CH3 CH3 │ │ C = C │ │ H H

CH3 H

│ │ C = C │ │ H CH3

Cis but-2-enem/p : -139C ↓

Trans but-2-enem/p: -106C ↑

Cis melting point is lower ↓• Bend structure (kink) prevent molecules from interacting /pack together• Less surface area due to bend/spherical structure• Lower intermolecular forces of attraction – lower melting point ↓

Trans melting point higher ↑• Linear structure – molecules interacting/ pack together • More surface area due to linear structure• Greater intermolecular forces of attraction – higher melting point ↑

Cis

Isom

er

Trans

Isomer


of atoms





CI H │ │ C = C │ │ H CI CH2 –CH = CH–CH2

CH3 CH3 │ │ C = C │ │ H H

CH3 H

│ │ C = C │ │ H CH3

Cis

Isom

er

Trans

Isomer

Cis boiling point is higher ↑ Trans boiling point lower ↓

Cis 1, 2 dichloroetheneb/p : 60C ↑

Cis but-2-eneb/p : 4C ↑

Trans 1, 2 dichloroetheneb/p : 48C ↓

Trans but-2-eneb/p : 1C ↓


of atoms





CI H │ │ C = C │ │ H CI CH2 –CH = CH–CH2

CH3 CH3 │ │ C = C │ │ H H

CH3 H

│ │ C = C │ │ H CH3

Cis

Isom

er

Trans

Isomer

Cis boiling point is higher ↑• CI groups are on same side- Bond polarity- Net dipole moment• Cis molecule is polar – Dipole interaction• Stronger intermolecular forces of attraction – Higher boiling point ↑

Trans boiling point lower ↓ • CI groups on diff side – Bond polarity cancel – No net dipole moment• Trans molecule is non polar – No Dipole interaction• Weaker intermolecular forces attraction – Lower boiling point ↓

Cis 1, 2 dichloroetheneb/p : 60C ↑

Cis but-2-eneb/p : 4C ↑

Trans 1, 2 dichloroetheneb/p : 48C ↓

Trans but-2-eneb/p : 1C ↓


of atoms

HOOC–CH = CH–COOH

HOOC COOH │ │ C = C │ │ H H

Cis butene dioic acidm/p: 130 ↓

Decomposes at 130C

HOOC H │ │ C = C │ │ H COOH

Trans butene dioic acidm/p: 286 ↑

Decomposes at 280

Cis melting point lower ↓• COOH same side – intramolecular hydrogen bonding• Less H atoms available for hydrogen bonding between molecules• Lower intermolecular forces attraction- m/p lower ↓

Trans melting point higher ↑• COOH opposite side – intermolecular hydrogen bonding• More H atoms available for hydrogen bonding between molecules• Higher intermolecular forces attraction – m/p higher ↑

Cis

Isom

er

Trans

Isomer





of atoms




Decomposes at 130C



Decomposes at 280



Cis

Isom

er

Trans

Isomer

Cis decomposes at lower temperature ↓• COOH same side – undergo condensation when heated• Loss of water molecule forming anhydride

Trans decomposes at higher temperature ↑• COOH opposite side – condensation of water molecule happens at higher temperature





of atoms




Decomposes at 130C



Decomposes at 280



Cis

Isom

er

Trans

Isomer

Cis decomposes at lower temperature ↓• COOH same side – undergo condensation when heated• Loss of water molecule forming anhydride

Trans decomposes at higher temperature ↑• COOH opposite side – condensation of water molecule happens at higher temperature

O O= C C = O │ │ C = C │ │ H H





heated HOOC H │ │ C = C │ │ H COOH

heated


of atoms

Stable cause COOH at different sides, (no condensation)

C2 H2 CI2

Draw the structural formula of isomers having MF C2H2CI2, and state the type of isomerism

Questions on Structural and Geometrical Isomerism

Draw the structural formula of cyclic isomers having MF C3H4CI2, and state the type of isomerism

C3H4CI2

C2 H2 CI2

H H │ │ C = C │ │ CI CI

CI H │ │ C = C │ │ CI H


Both are Structural formula



C3H4CI2


C2 H2 CI2

H H │ │ C = C │ │ CI CI

CI H │ │ C = C │ │ CI H



Geometric IsomersCis/Tans isomerism

H H │ │ C = C │ │ CI CI

H CI │ │ C = C │ │ CI H

TransCis



C3H4CI2


Geometric IsomersCis/Tans isomerism

CisTrans


Which of the following exhibit cis/trans isomerism ?

Br H │ │ C = C │ │ Br H

CH3 CH3 │ │ C = C │ │ H H

H CH3 │ │ C = C │ │ CI CI

CH3CH=CH-CH3 CH3CH=CH2CH(CI)=CH(CI)-CH3

Which of the following is an structural isomer of CH3COCH2CH3?

CH2 = CH- CH-CH3

│ OH

CH3 –CH2-CH2-CH ║ O

CH3 –CH2- O- CH2-CH3

Draw the structural isomer for the following

CH3CH=CHCH2CH3 F-CH = CH-F

A B C

A B C

A B C


Which of the following exhibit cis/trans isomerism ?

Br H │ │ C = C │ │ Br H

CH3 CH3 │ │ C = C │ │ H H

H CH3 │ │ C = C │ │ CI CI

CH3CH=CH-CH3 CH3CH=CH2CH(CI)=CH(CI)-CH3

Which of the following is an structural isomer of CH3COCH2CH3?

CH2 = CH- CH-CH3

│ OH

CH3 –CH2-CH2-CH ║ O

CH3 –CH2- O- CH2-CH3

Draw the structural isomer for the following

CH3CH=CHCH2CH3 F-CH = CH-F

H H │ │ C = C │ │ CH3 CH2CH3

CH3 H │ │ C = C │ │ H CH2CH3

Cis pent-2-ene Trans pent-2-ene

F F │ │ C = C │ │ H H

Cis 1, 2 difluoroethene

F H │ │ C = C │ │ H F

Trans 1, 2 difluoroethene

A B C

A B C

A B C

√ √

√ √

√ √

X

X

X

Same atoms on carbon

Same atoms on carbon

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com

http://creativecommons.org/licenses/


Education

IB Chemistry on Structural Isomers, Geometric Isomers and Stereoisomerism