sevada chamras, ph.d. glendale community …4 indicate the location of the substituent(s) [side...

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Sevada Chamras, Ph.D.

Glendale Community College

Chemistry 105

Exam. 1 Lecture Notes

Chapters 1, 2, & 3

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CHAPTER 3

*** 3-D Molecular Model Set Needed***

Saturated Hydrocarbons (AKA: Alkanes) (AKA:Paraffins)

1. General Formula:

2. “Functional Group” or “Side Chain”:

2. General IUPAC Nomenclature for Alkanes:

C's Molecular Formula ! Name Functional GroupFormula ! Name

1 CH4 ! –CH3 !

2 ! !

3 ! !

4 ! !

5 ! !

6 ! !

7 ! !

8 ! !

9 ! !

10 ! !

11 ! !

12 ! !

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***Note: Only 4 bonds are extended from carbons, and only 1 bond is extended from

hydrogens.

3. Isomerism in Hydrocarbons:

n-alkanes:

Constitutional isomers of n-alkanes:

EXAMPLE:

Methane: (1)

Ethane: (1)

Propane: (1)

Butane: (2)

Pentane: (3)

Hexane: (5)

How many isomers? Is there a predicting formula?

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4. IUPAC Nomenclature Steps and Rules for Alkanes:

• Locate the longest continuous chain! This will be used as the name of the base compound

Example:

***What if there is more than 1 longest continuous chain?

Example:

• Number the carbons in the main chain.

***Note: There are 2 ways (from 2 ends) of numbering the chain. Choose the end as the #1

carbon that is nearest to the substituent.

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Indicate the location of the substituent(s) [side chain(s)].

When there is more than one side chain, the correct way for naming should have the

side-chains mentioned by alphabetical order.

When two or more of the side chains are the same, use numbering prefixes like di, tri,

tetra, etc. …, in order to avoid repetition of the names for the side chains.

Numbers are separated from each other with commas.

Numbers are separated from letters with dashes.

Types of Carbons Based on Substitution:

1. Methyl:

2. Primary:

3. Secondary:

4. Tertiary:

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Some Common Side Chains:

CH3

CH

H3C

CH3CH3C

CH3H3C

CH

H2C

CH3

H3C

CH2

H2C

H3C

H2C

CH2

H2C

H3C

H2C

CH

CH3

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Examples for Naming More Complex Side Chains:

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Physical Properties of Alkanes:

a) Solubility (Polarity):

b) Average Density:

c) Melting Point:

What Happens at Melting Point?

1. The Effect of Molar Mass:

CH CH

CH3CH2H3C

VCH3

H3C

C

H2C

CH

CH3

CH3CH3

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2. The Odd-Even Carbon Effect:

3. The Effect of Branching:

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Structure & Conformation of Alkanes:

1. Hybridization and Structure of Carbons in Alkanes:

Hybridization ! Bonds ! Geometry ! Ideal Bond Angle

2. What is Conformation?

3. What is Free Rotation?

4. What is Conformational Isomer? (Conformer)

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5. An Initial Look at Ethane and Its Two Possible Conformations:

***Drawing 3-Dimensional (Wedge-Dash) Structures: (Use the model set now)

Drawing Tools

a) Draw the carbon skeleton in the plane of the paper, showing the carbons:

Ethane Propane

CH3H3C

C2H6Molecular Formula:

Condensed Formula: H3CCH3

Bond-Line Formula:

Expanded Structural Formula: C C

H

H

H

H

H

H

3-Dimensional Structural Formula:

(AKA: Wedge-Dash)

Wedge DashLine

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b) Add in the hydrogens using the wedges, the dashes, and the straight lines:

Ethane Propane

6. Two Methods for Structure Drawing to Study Conformers More Effectively:

a) Newman Projection: (Viewing the molecule along the C-C bond axis)

• Draw two possible Wedge-Dash structure for Ethane:

Structure A Structure B

• Convert the Wedge-Dash to Newman Projection by looking at it through the C-C

bond of ethane: (Construct the model and view it along the C-C axis)

Structure A Structure B

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Names for Structures (conformers) A and B, based on the relative orientations of the hydrogen

atoms on the carbons:

Structure A:

Structure B:

Energetic Relation between Eclipsed and Staggered Conformers:

Reason for the Energetic Trend:

• Dihedral Angle (! ): Definition: ___________________________________

b) Sawhorse Projection:

• Start with the Newman Projection for each conformer drawn above:

• In your mind (or using the model set now) rotate the molecule thus tilting it

enough to be able to see the C-C bond:

• Draw what you see:

Eclipsed Staggered

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Conformational Analysis of Ethane: Study of the change in the potential energy of ethane as

a function of rotation around C-C bond (change in the dihedral angle size):

Dihedral Angle (o)

Conformational Analysis of Butane:

Dihedral Angle (o)

New Words:

Gauche Conformer:

Anti Conformer:

Tortional Strain (Tortional Energy):

Steric Strain (Steric Energy):

E

0o 60o 120o 180o

E

0o 60o 120o 180o 240o 300o 360o

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Cyclic Saturated Hydrocarbons (AKA: Cycloalkanes)

• General Formula:

• Naming Unsubstituted Cyclic Alkanes:

___________________ ___________________ ___________________

___________________ ___________________ ___________________

• Naming Substituted Cyclic Alkanes:

1. With one substituent: Similar to open-chain alkanes:

Example:

___________________ ___________________

2. With more than one substituent:

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• Number the ring carbons. The correct direction for numbering is the one that results in

the smallest numbers for the substituents:

Example:

________________________

________________________

• When the open chain contains more carbons than the ring, the open chain becomes the

main compound, and the ting becomes a substituent (side chain).

Example:

________________________

__________________________________________________________________________

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Conformations in Cycloalkanes:

1. Cyclopropane: An equilateral triangle (seemingly). Angles: 60o vs. 72

o.

Bent Bonds:

Strengtth of the C-C bonds:

Angle Strain: sp3 angle = 109.5

o, C-C-C angle in cyclopropane =

2. Cyclobutane: Flat vs. puckered ring:

Angles = 90o

109.5o>Angles > 90

o

3. Cyclopentane: Angle = 108o

Three conformations:

Planar Envelope Half-Chair

More torsional Less Torsional Less Torsional

Strain Strain Strain

60o

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4. Cyclohexane: Virtually free of torsional and angle strain.

Conformations: Chair, boat, twist-boat.

Drawing the Chair Conformer

a) Drawing the carbon skeleton:

1. Draw 2 parallel lines as shown:

2. Draw another set of two parallel lines stemming from the end of one and the beginning

of the other line:

3. Connect the two bent shapes to complete the carbon skeleton of the ring:

b) Drawing in the substituents (hydrogens in case of an unsubstituted cyclohexane):

1. The axial substituents are drawn as vertical lines pointing above and below the plane of

the ring in an alternating fashion.

Hint: Start with the higher tip of the ring and have the substituent pointing above the plane

of the ring.

H

H

H

H

H

H

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2. The equatorial substituents are drawn as tilted straight lines pointing above and below the

plane of the ring, and directed away from the body of the ring. If the axial substituent points

above the plane, then the axial should point below, and vice versa.

*Hint: To get a better, more precise idea on the exact direction of the equatorial substituents, 4

of the 6 equatorial substituents are parallel to 4 C-C bonds of the ring. The picture below

illustrated the corresponding parallel pairs:

Conformation Conversions in Cyclohexane:

Chair 1 "! Half-Chair 1 "! Twist Boat "! Half-Chair 2 "! Chair 2

Energetic comparison of the conformers:

.Chairs:

.Half-Chairs:

.Twist Boat: E

Boat

H

H

H

H

H

H

HH

H

H

H

H

H

H

H

H

H

H

HH

H

H

H

H

1

1

2

2

3

3

4

4

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Flipping Chairs!

Substituted Cyclohexanes:

1,3-Diaxial Interaction:

Equilibrium between the chair forms of mono-substituted cyclohexanes:

1

4

7

12

9

6

211

3

5

8

10

H

H

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Disubstituted Cyclohexanes:

Cis & trans Substituents:

Cis-

Trans-

1. 1,2 substitution:

2. 1,3 substitution:

3. 1,4 substitution:

Examples of disubstituted cyclohexanes and the equilibria for the chair conformers.

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Bicyclic Compounds:

Compounds containing 2 joined rings.

Types: 1. Brigded

2. Fused EXAMPLES

3. Spirocyclic

Nomenclature:

a) For Bridged and Fused:

• Locate the bridgehead.

• Count the number of carbons in each bridge, excluding the bridgehead

carbons.

• Start with the prefix “bicyclo”

• Follow with the bridge count in decreasing order of carbons.

• List the name of the alkane matching the total number of carbons in the

bicyclic compound.

Example:

____________________________ _______________________________

b) For Spirocyclics:

• Start with the prefix “spiro”

• Count the carbons of the two tethered portions joined at one point, excluding the

spiro carbon.

• Follow with the tether count in decreasing order of carbons.

• List the name of the alkane matching the total number of carbons in the spiro

compound.

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Example:

__________________________