Hydrocarbons

CxHy

Hydrides of Carbon

C

H

HH

H

Carbonhas fourvalence electrons.Wants to form fourbonds.

Hydrogen has one valenceelectron and wants to form one bond

Methane

C

H

HH

H

Ethane

C

H

CH

H

H

H

H

C

H

CH

H

H

C

H

H

H

H

Propane

C

H

CH

H

H

C

H

H

H

C

H

H

H

Butane

Methane CH4 Ethane C2H6

Propane C3H8 Butane C4H10

Compound Formula Melting Pt. ºC Boiling Pt. ºC

methane CH4 -182.5 -162ethane CH3CH3 -183.3 -88.6n-propane CH3CH2CH3 -187.7 -42.1n-butane CH3(CH2)2CH3 -138.3 -0.5n-pentane CH3(CH2)3CH3 -129.8 36.1n-hexane CH3(CH2)4CH3 -95.3 68.7n-heptane CH3(CH2)5CH3 -90.6 98.4n-octane CH3(CH2)6CH3 -56.8 125.7n-nonane CH3(CH2)7CH3 -53.5 150.8n-decane CH3(CH2)8CH3 -29.7 174.0n-undecane CH3(CH2)9CH3 -25.6 195.8n-dodecane CH3(CH2)10CH3 -9.6 216.3n-eicosane CH3(CH2)18CH3 36.8 343

Ethane Conformations

Staggered Eclipsed

0 60 120 180 240 300 360

Angle of Rotation, degrees

12 kJ

Variation of Energy with Rotation of C-C bond in Ethane

Butane C4H10 n- 2-methylpropaneor isobutane

These two molecules are structural isomers.

They differ in the way their atoms are connected

They have different chemical and physicalproperties.

2-methylpropaneor isobutane

CC

C

C

H

HHH

HH

HH

HH

CH3CH(CH3)CH3

n-hexane

These structures represent differentconformations of n-hexane, not isomers.

n-hexane 2-methylpentane

3-methylpentane4-methylpentane

2,3-dimethylbutane 2,2-dimethylbutane

The Same

These are the five isomers of hexane, C6H14

Methane becomes Methyl

Ethane becomes Ethyl

Propane becomes Propyl

C H

H

HHC

H

HH

C H

CH3

HHC

CH3

HH

C H

CH3CH2

HHC

CH3CH2

HH

1 Methane Methyl2 Ethane Ethyl3 Propane Propyl4 Butane Butyl5 Pentane Pentyl6 Hexane Hexyl7 Heptane Heptyl8 Octane Octyl9 Nonane Nonyl10 Decane Decyl

12

3

4

56

7

Find the longest chain 7 carbons. It’s a heptane

Number the atoms

Add the substituents inalphabetic order

4-ethyl-2-methylheptane

5 carbon chain. It’s a pentane

3 methyls so use the prefix - tri

2 di-3 tri-4 tetra-5 penta-6 hexa-

2,2,4-trimethylpentane

not

4,4,2-trimethylpentane

9 carbon chain

It’s a nonane

2 methyl groups and1 ethyl group

4-ethyl-3,7-dimethylnonane

not

6-ethyl-3,7-dimethylnonane

hexane2-methylpentane

3-methylpentane

2,3-dimethylbutane

2,2-dimethylbutane

What is special about this compound?

3-methylhexane

These two compounds are different.

CH3 H H CH3

One Is left handed and the other is right handed.

The two compounds are mirror images.

Put your thumb toward you representing the hydrogenatom, the lightest group. Point your fingers toward thepropyl group, the heaviest group. Curl your fingerstoward the ethyl group, the second heaviest group.

Left Handed or S Right Handed or R

These molecules are Chiral. They have handedness.

S-3-ethyl-2-methylhexane

H

Molecular Formulas for Alkanes

are all of the form CnH2n+2

2,2,4-trimethylpentanen-octane

n = 8 2n + 2 = 18 C8H18

Molecular Formulas for Alkenes

are all of the form CnH2n

2,4,4-trimethyl-2-pentene1-octene

n = 8 2n = 16 C8H16

H

H

H H

cis-2-pentenetrans-2-pentene

If an alkene has two identical substituents on the twodifferent carbons, they can be named cis or trans.

If the identical substituents are on the same side we call themolecule cis. If they are on opposite sides we call the molecule trans.

The two compounds shown above are stereoisomers.

If two substituents on one carbon are the samecis and trans do not apply

But what do we do if all groups are different?

Instead of cis or trans use E or Z

Z means the two heaviest groups are on thesame side of the double bond.

E means the two heaviest groups are on different sides of the double bond.

(E) - 3-methyl-3-heptene (Z) - 3-methyl-3-heptene

cis-3,5-dimethyl-2-hexene

(E)-2,4-dimethyl-3-hexene

2-ethyl-4-methyl-1-pentene

Molecular Formulas for Alkynes

are all of the form CnH2n-2

1-octyne

n = 8 2n - 2 = 14 C8H14

H

2-methyl-3-hexyne

3-ethyl-6-methyl-1-heptyne

trans-2-pentene cyclopentane

C5H10

Cycloalkanes CnH2n

cyclopropane cyclobutane

cyclopentane cyclohexane

60

Cyclopropane

CH3 H

CH3H

CH3 CH3

HH

cis-1,2-dimethylcyclopropane

trans-1,2-dimethylcyclopropane

trans-1,2-dimethycyclobutane

cis-1-ethyl-3-methylcyclobutane

120

Cyclohexane

Ideal angles are 120 degrees.

Actual angles are 109.5degrees, the tetrahedral angle

Benzene

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

1,3-dimethylbenzene

1,4-dimethylbenzene

1,2-dimethylbenzenemethylbenzene

toluene

ortho

meta para

Draw all compounds of formula C4H8

Draw all compounds of formula C4H6

Draw all compounds of formula C4H10