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Structure of Alkanes: Different Representa4ons of Organic Molecules

The document discusses the structures, properties, and nomenclature of alkanes and cycloalkanes. It provides examples of drawing line structures, determining molecular formulas, identifying functional groups, giving IUPAC names, and depicting conformations using Newman projections. Resonance structures, constitutional isomers, chair conformations, and cis-trans isomers are also explained. Ranking of boiling points based on molecular polarity is demonstrated.

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Janice Chua
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46 views11 pages

Structure of Alkanes: Different Representa4ons of Organic Molecules

The document discusses the structures, properties, and nomenclature of alkanes and cycloalkanes. It provides examples of drawing line structures, determining molecular formulas, identifying functional groups, giving IUPAC names, and depicting conformations using Newman projections. Resonance structures, constitutional isomers, chair conformations, and cis-trans isomers are also explained. Ranking of boiling points based on molecular polarity is demonstrated.

Uploaded by

Janice Chua
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Structure

of Alkanes
Dierent representa4ons of organic molecules
Draw the line-structure for the following molecules.
H H C H H H H C H C H C H C H H

H
H C H H

H C C C C C H CH2 CH CH3 CH3

C H

What is the molecular formula of the following molecules? Also iden4fy func4onal groups in each molecule.
HO HO O HO OH glucose OH

O OH NH2 phenylalanine

C6H12O6

C9H11NO2

Structure of Alkanes
Dierent representa4ons of organic molecules
Give the resonance structures of the following molecules.

O N O

O N O N

O O

O N O

Cons4tu4onal Isomerism
Cons4tu4onal isomers
Same formula but have dierent connec4vity

Draw three cons4tu4onal isomers with the formula C3H6O. Use line structures.
O O OH

OH

OH

OH

Alkane Nomenclature
Give the IUPAC names of the following alkanes.
5 6 7 4 3

2 1

2-methylbutane

2-methyl-4-(1-methylethyl)heptane or 4-isopropyl-2-methylheptane
7 6 9 8 10

4 3

8 7
1

2 3

1 2

2,6-dimethyl-5-propyloctane

5-butyl-5-(2-methylpropyl)decane

Cycloalkanes
What are the IUPAC names of the following cycloalkanes?

1-ethyl-1-methylcyclopropane

2-ethyl-1,4-dimethylcyclohexane

1-ethyl-4-(1,1-dimethylethyl) cyclohexane or 1-tert-butyl-4-ethylcyclohexane

(1,2-dimethylbutyl)cycloheptane

Bicycloalkanes
Alkanes with two rings (CnH2n-2)
Carbons divided into bridgehead carbons and bridge carbons
1 2 3 0 3 1

2 3 1

2
2

3 4

1 3

bicyclo[3.3.0]octane

bicyclo[4.3.3]dodecane

IUPAC naming
Add prex bicyclo- to name of alkane with same number of carbons Indicate bridge lengths in brackets in decreasing order What are the IUPAC naming of the following molecules?

bicyclo[2.2.2]octane

bicyclo[4.2.0]octane

Alkane and Cycloalkane Conforma4ons


Alkane
Newman projec4on View of molecule down a C-C bond
H H H H H
H H H H H H

H H

H H

Draw a Newman projec4on for propane. Place C1 in front.

Draw the Newman projec4on for the conforma4on shown below. Look down the C2-C3 bond with C3 in front.
3 2

H H

CH3

H H

H H

CH3

CH3 OH

OH

Et

Alkane and Cycloalkane Conforma4ons


Draw the Newman projec4ons for the most and least stable conforma4ons of 2,3,4-trimethylpentane looking down the C2-C3 bond.
iPr CH3 H3C H3C H H

least stable

H H3C

iPr

CH3 H

H3C H3C

iPr

H H

H3C H3C

iPr

CH3 H

CH3

CH3

1 Me-iPr Gauche 1 Me-Me Gauche most stable

1 Me-iPr Gauche 2 Me-Me Gauche

2 Me-iPr Gauche 1 Me-Me Gauche

Alkane and Cycloalkane Conforma4ons


Cycloalkanes
Draw the two chair conforma4ons of the following molecules. Is the equilibrium constant = 1, > 1 or < 1?

K < 1 trans

cis

K > 1

Cis, Trans Isomersim in Cycloalkanes


Stereoisomers
Compounds with same molecular formula, same connec4vity but dierent orienta4on of atoms in space Cis and trans isomers have subs4tuents on the same side and opposite side of the ring respec4vely

Draw the two chair conforma4ons of cis-1-uoro-2-methylcyclohexane. Is the K = 1, >1 or < 1?


F F

K < 1

Physical Proper4es
Alkanes nonpolar
Rank the following molecules in order of increasing bp.
NaOH A B C

F3C D E

E < A < C < D < B

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