Che 163Introductory Organic Chemistry

ALKANESSummer Quarter 2010

What is Organic chemistry?

What is Organic chemistry?

The study of carbon and its compounds.

What is Organic chemistry?

The study of carbon and its compounds.

First we will concentrate on compounds just containing carbon and hydrogen, these compounds are called hydrocarbons.

What is Organic chemistry?

The study of carbon and its compounds.

First we will concentrate on compounds just containing carbon and hydrogen, these compounds are called hydrocarbons.

Hydrocarbon Classification

Hydrocarbons

Alkanes AlkenesCycloalkanes AlkynesCycloalkenes

1. Alkanes (saturated) hydrocarbons, or aliphatic hydrocarbons)

A. General formula of CnH2n+2

B. Examples

a. CH4 b. C2H6 c. C3H?

1. Alkanes

A. General formula of CnH2n+2

B. Examples

a. CH4 b. C2H6 c. C3H8 d. C4H?

1. Alkanes

A. General formula of CnH2n+2

B. Examples

a. CH4 b. C2H6 c. C3H8 d. C4H10

C. Draw Lewis Structures

CH4 C2H6 C3H8

1. Alkanes

A. General formula of CnH2n+2

B. Examples

a. CH4 b. C2H6 c. C3H8 d. C4H10

C. Draw Lewis Structures

CH4 C2H6 C3H8

D. Polarity? Polar or nonpolar?

1. Alkanes

A. General formula of CnH2n+2

B. Examples

a. CH4 b. C2H6 c. C3H8 d. C4H10

C. Draw Lewis Structures

CH4 C2H6 C3H8

D. Polarity? Polar or nonpolar? Nonpolar

1. Alkanes (Continued)

E. Draw three dimensional structures, bond angles and hybridization.

CH4 C2H6 C3H8

F. There are two different structures for C4H 10

Structure 1

Structure 2

G. Types of carbon 1. Primary (1◦) Carbon connected to one carbon atoms. 2. Secondary (2◦) Carbon connected to two carbon atoms. 3. Tertiary (3◦) Carbon connected to three carbon atoms. 4. How many primary, secondary, and tertiary carbons in the

two different structures of C4H10

C

H

C

H

H

H C C

H

HH H

H

H

Butane, C4H10 =>

C

H

C

H

H

H C H

H

HC H

H

H

Isobutane, C4H10

Primary = ?Secondary = Tertiary =

Primary =Secondary = Tertiary =

G. Types of carbon 1. Primary (1◦) Carbon connected to one carbon atoms. 2. Secondary (2◦) Carbon connected to two carbon atoms. 3. Tertiary (3◦) Carbon connected to three carbon atoms. 4. How many primary, secondary, and tertiary carbons in the

two different structures of C4H10

C

H

C

H

H

H C C

H

HH H

H

H

Butane, C4H10 =>

C

H

C

H

H

H C H

H

HC H

H

H

Isobutane, C4H10

Primary = 2Secondary = ? Tertiary =

Primary =Secondary = Tertiary =

G. Types of carbon 1. Primary (1◦) Carbon connected to one carbon atoms. 2. Secondary (2◦) Carbon connected to two carbon atoms. 3. Tertirary (3◦) Carbon connected to three carbon atoms. 4. How many primary, secondary, and tertiary carbons in the

two different structures of C4H10

C

H

C

H

H

H C C

H

HH H

H

H

Butane, C4H10 =>

C

H

C

H

H

H C H

H

HC H

H

H

Isobutane, C4H10

Primary = 2Secondary = 2 Tertiary = ?

Primary =Secondary = Tertiary =

G. Types of carbon 1. Primary (1◦) Carbon connected to one carbon atoms. 2. Secondary (2◦) Carbon connected to two carbon atoms. 3. Tertiary (3◦) Carbon connected to three carbon atoms. 4. How many primary, secondary, and tertiary carbons in the

two different structures of C4H10

C

H

C

H

H

H C C

H

HH H

H

H

Butane, C4H10 =>

C

H

C

H

H

H C H

H

HC H

H

H

Isobutane, C4H10

Primary = 2Secondary = 2 Tertiary = 3

Primary = ?Secondary = Tertiary =

G. Types of carbon 1. Primary (1◦) Carbon connected to one carbon atoms. 2. Secondary (2◦) Carbon connected to two carbon atoms. 3. Tertiary (3◦) Carbon connected to three carbon atoms. 4. How many primary, secondary, and tertiary carbons in the

two different structures of C4H10

C

H

C

H

H

H C C

H

HH H

H

H

Butane, C4H10

C

H

C

H

H

H C H

H

HC H

H

H

Isobutane, C4H10

Primary = 2Secondary = 2 Tertiary = 3

Primary = 3Secondary = ? Tertiary =

G. Types of carbon 1. Primary (1◦) Carbon connected to one carbon atoms. 2. Secondary (2◦) Carbon connected to two carbon atoms. 3. Tertiary (3◦) Carbon connected to three carbon atoms. 4. How many primary, secondary, and tertiary carbons in the

two different structures of C4H10

C

H

C

H

H

H C C

H

HH H

H

H

Butane, C4H10

C

H

C

H

H

H C H

H

HC H

H

H

Isobutane, C4H10

Primary = 2Secondary = 2 Tertiary = 3

Primary = 3Secondary = 0 Tertiary = ?

G. Types of carbon 1. Primary (1◦) Carbon connected to one carbon atoms. 2. Secondary (2◦) Carbon connected to two carbon atoms. 3. Tertiary (3◦) Carbon connected to three carbon atoms. 4. How many primary, secondary, and tertiary carbons in the two different structures of C4H10

C

H

C

H

H

H C C

H

HH H

H

H

Butane, C4H10

C

H

C

H

H

H C H

H

HC H

H

H

Isobutane, C4H10

Primary = 2Secondary = 2 Tertiary = 3

Primary = 3Secondary = 0 Tertiary = 1

Constitutional Isomers (Structural Isomers) are different compounds of the same formula. The different structures from the previous slide for the formula C4H10 is an example of Constitutional isomers.

How many isomers are there of an alkane containing five carbons (C5H10)?

NOMENCLATURE1.Common system

a. Works best for low molecular weight hydrocarbonsb. Steps to give a hydrocarbon a common name:

1. Count the total number of carbon atoms in the molecule.

2. Use the Latin root from the following slide that corresponds to the number of carbon atoms followed by the suffix “ane”.

3. Unbranced hydrocarbons use the prefix normal, or n-, 4. Branched hydrocarbons use specific prefixes, as

shown on a subsequent slide

Latin Hydrocarbon

RootsNumber of Carbons

LatinRoot

1 meth

2 eth

3 prop

4 but

5 pent

6 hex

7 hept

8 oct

9 non

10 dec

11 undec

Latin Hydrocarbon

RootsNumber of Carbons

LatinRoot

12 dodec

13 tridec

14 tetradec

15 pentadec

16 hexadec

17 heptadec

18 octadec

19 nonadec

20 eicos

21 unicos

22 doicos

C

H

H

H

C

H

C

H

HH

C

H

H

H

CH

H

H

C

CH H

C

HH

H H

H

n-butane

isobutane

H C C C H

H C H

H C H

H

H

H

H H

H

Examples

neopentane

2. Systematic System of Nomenclature (IUPAC)

•Find the longest continuous chain of carbon atoms.•Use a Latin root corresponding to the number of carbons in the longest chain of carbons.•Follow the root with the suffix of “ane” for alkanes•Carbon atoms not included in the chain are named as substituents preceding the root name with Latin root followed by “yl” suffix.•Number the carbons, starting closest to the first branch.•Name the substituents attached to the chain, using the carbon number as the locator in alphabetical order.•Use di-, tri-, etc., for multiples of same substituent.• If there are two possible chains with the same number of carbons, use the chain with the most substituents.

Substituent Names (Alkyl groups)

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

Which one?

Systematic Nomenclature continued.

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

Which one?

Systematic Nomenclature continued.

The one with the most number of substituents

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

Which one?

Systematic Nomenclature continued.

The one with the least number of substituents

The top structure has four substituents and the bottom has threeSubstituents.

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

Which one?

Systematic Nomenclature continued.

The one with the least number of substituents

The top structure has four substituents and the bottom has threeSubstituents.

Name = ?

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

Which one?

Systematic Nomenclature continued.

The one with the least number of substituents

The top structure has four substituents and the bottom has threeSubstituents.

Name = ? heptane

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

Which one?

Systematic Nomenclature continued.

The one with the least number of substituents

The top structure has four substituents and the bottom has threeSubstituents.

Name = 3,3,5-trimethyl-4-propylheptane

CHH3C

CH3

CH

CH2CH3

CH2 CH2 CH

CH3

CH3

Another Example:

Name = 3-ethyl-2,6-dimethylheptane

CHH3C

CH3

CH

CH2CH3

CH2 CH2 CH

CH3

CH3

Another Example:

Name = 2,6-dimethyl-3-ethylheptane

Notice substituents are in alphabetical order; di, tri, etc. do not participate in the alphabetical order

Line StructuresA quicker way to write sturctures

CHH3C

CH3

CH

CH2CH3

CH2 CH2 CH

CH3

CH3 (Condensed Structure)

(A line structure of the above condensed structure)

ethyl

methyl

methyl

Complex Substituents•If the branch has a branch, number the carbons from the point of attachment.•Name the branch off the branch using a locator number.•Parentheses are used around the complex branch name.

1-methyl-3-(1,2-dimethylpropyl)cyclohexane

12

13

Alkane Physical PropertiesSolubility: hydrophobic (not water soluble)Density: less than 1 g/mL (floats on water)

Boiling points increase with increasing carbons (little less for branched chains) due to dispersion forces being larger.

Melting points increase with increasing carbons (less for odd-number of carbons).

Boiling Points of AlkanesBranched alkanes have less surface area contact,so weaker intermolecular forces.

Melting Points of AlkanesBranched alkanes pack more efficiently into a crystalline structure, so have higher m.p.

Reactions of AlkanesI. Combustion reaction

CH

H

H

H + O2

heatCO2 + H2O

+ O2

heatCO2 + H2O

II. Cracking reactionheat

catalyst

+

III. Halogenation reaction (substitution reaction)

+ Cl2

+ HCl+

Cl Cl

Butane 2-chlorobutane 1-chlorobutane

sun

Sample problem: Which isomer of C5H12 has the most monochloro isomers?

Problem solving process:Step 1 draw the isomers of C5H12

Step 2 react each isomer with chlorineStep 3 count the products

Sample problem: Which isomer of C5H12 has the most monochloro isomers?

Problem solving process:Step 1 draw the isomers of C5H10

Step 2 react each isomer with chlorineStep 3 count the products

+ Cl2

+ Cl2

+ Cl2

Sample problem: Which isomer of C5H12 has the most monochloro isomers?

Problem solving process:Step 1 draw the isomers of C5H10

Step 2 react each isomer with chlorineStep 3 count the products

+ Cl2

+ Cl2

+ Cl2

Cl

Cl

Cl

+ +

2-chloropentane 1-chloropentane 3-chloropentane

Sample problem: Which isomer of C5H12 has the most monochloro isomers?

Problem solving process:Step 1 draw the isomers of C5H10

Step 2 react each isomer with chlorineStep 3 count the products

+ Cl2

+ Cl2

+ Cl2

Cl

Cl

Cl

+ +

2-chloropentane 1-chloropentane 3-chloropentane

Cl

ClCl

Cl

1-chloro-3-methylbutane 2-chloro-3-methylbutane 2-chloro-2-methylbutane 1-chloro-2-methylbutae

Sample problem: Which isomer of C5H12 has the most monochloro isomers?

Problem solving process:Step 1 draw the isomers of C5H10

Step 2 react each isomer with chlorineStep 3 count the products

+ Cl2

+ Cl2

+ Cl2

Cl

Cl

Cl

+ +

2-chloropentane 1-chloropentane 3-chloropentane

Cl

ClCl

Cl

1-chloro-3-methylbutane 2-chloro-3-methylbutane 2-chloro-2-methylbutane 1-chloro-2-methylbutae

Cl

1-chloro-2,2-dimethylpropane

Sample problem: Which isomer of C5H12 has the most monochloro isomers?

Problem solving process:Step 1 draw the isomers of C5H10

Step 2 react each isomer with chlorineStep 3 count the products

+ Cl2

+ Cl2

+ Cl2

Cl

Cl

Cl

+ +

2-chloropentane 1-chloropentane 3-chloropentane

Cl

ClCl

Cl

1-chloro-3-methylbutane 2-chloro-3-methylbutane 2-chloro-2-methylbutane 1-chloro-2-methylbutae

Cl

1-chloro-2,2-dimethylpropane

Winner!

Conformers of Alkanes

•Structures resulting from the free rotation of a C-C single bond•May differ in energy. The lowest-energy conformer is most prevalent.•Molecules constantly rotate through all the possible conformations.

Ethane ConformersStaggered conformer has lowest energy.Dihedral angle = 60 degrees

model

H

H

H

H

H H

Newmanprojection sawhorse

Dihedral angle

Ethane Conformers (2)Eclipsed conformer has highest energyDihedral angle = 0 degrees

=>

Conformational Analysis•Torsional strain: resistance to rotation.•For ethane, only 12.6 kJ/mol

=>

Propane ConformersNote slight increase in torsional straindue to the more bulky methyl group.

Butane Conformers C2-C3Highest energy has methyl groups eclipsed.Steric hindranceDihedral angle = 0 degrees

=>totally eclipsed (methyl groups)

Butane Conformers (2)Lowest energy has methyl groups anti.Dihedral angle = 180 degrees

=>Staggered-anti

Butane Conformers (3)•Methyl groups eclipsed with hydrogens•Higher energy than staggered conformer•Dihedral angle = 120 degrees

=>Eclipsed (hydrogen and methyl)

Butane Conformers (4)•Gauche, staggered conformer•Methyls closer than in anti conformer•Dihedral angle = 60 degrees

=>Staggered-gauche

Conformational Analysis

Cycloalkanes

•Rings of carbon atoms (-CH2- groups)

•Formula: CnH2n

•Nonpolar, insoluble in water•Compact shape•Melting and boiling points similar to branched alkanes with same number of carbons•Slightly unsaturated compared to alkanes

Naming Cycloalkanes•Count the number of carbons in the cycle•If the bonds are single then use the suffix “ane”•First substituent in alphabet gets lowest number.•May be cycloalkyl attachment to chain.

cyclopropane cyclobutane cyclopentane cyclohexane cycloheptane

mehtylcyclopropane 1-ethyl-2-methylcyclobutane

CH3 H3CH2C CH3

2-cyclopropylheptane

Cis-Trans Isomerism(a type of stereoisomerism)

Cis: like groups on same side of ringTrans: like groups on opposite sides of ring

Cycloalkane Stability• 6-membered rings most stable• Bond angle closest to 109.5• Angle (Baeyer) strain• Measured by heats of combustion per -CH2 -

Heats of Combustion/CH2 Alkane + O2 CO2 + H2O

658.6

697.1 686.1664.0 663.6 kJ/mol

662.4658.6 kJ

Long-chain

Cyclopropane

• Large ring strain due to angle compression• Very reactive, weak bonds

=>

Cyclopropane (2)

Torsional strain because of eclipsed hydrogens

Cyclobutane• Angle strain due to compression• Torsional strain partially relieved by ring puckering

=>

Cyclopentane• If planar, angles would be 108, but all hydrogens would be eclipsed.• Puckered conformer reduces torsional strain.

Cyclohexane• Combustion data shows it’s unstrained.• Angles would be 120, if planar.

• The chair conformer has 109.5 bond angles and all hydrogens are staggered.

• No angle strain and no torsional strain.

Chair Conformer

Boat Conformer

Conformational Energy

Axial and Equatorial Positions

Monosubstituted Cyclohexanes

1,3-Diaxial Interactions

Disubstituted Cyclohexanes

Cis-Trans IsomersBonds that are cis, alternate axial-equatorial around the ring.

=>

CH3

CH3

One axial, one equatorial

Bulky Groups• Groups like t-butyl cause a large energy difference between the axial and equatorial conformer. • Most stable conformer puts t-butyl equatorial regardless of other substituents.

=>

End of Chapter 2