Chapter 11 Organic Chemistry

The study of the compounds of carbon

Some Properties Typical of Organic Compounds

Organic compounds form covalent bondshave low melting points and boiling pointstend to be flammableare soluble in non-polar solventsare not very soluble in water

Oil and waterA Review of the Bonding in Carbon

Compounds of Carbon and Hydrogen

Carbon has 4 valence electrons, and hydrogen has 1;

to achieve an octet, C forms four bonds

We will use a line __ to indicate the sharing of 2 electrons

You may recall that when 4 groups are attached to a central atom, the groups arrange themselves so they point to the corners of a tetrahedron

The following illustrates 4 different but equivalent ways of illustrating the structure of methane:

Compound solely of carbon and hydrogen are called hydrocarbons;

if more than on carbon atom is present, then the molecule must have carbon-carbon bonds. The molecule shown below is called ethane

CH3CH3 different ways of writing ethane

If carbon can form stable bonds to itself, there is no reason why there can’t be hydrocarbon composed of more than 2 carbons

Butane (butane lighter) has the following structures:

Although the two forms of butane shown differ in the orientation of the CH3 groups circled, rotation of the groups as shown occurs quite rapidly

Butane, C4H10 has one other feature worth describing.

In the structure shown above, each carbon is either attached to one or two other carbon atoms.Consider a different way in which these four carbon atoms can be attached

The lower molecule is called isobutane

If we consider hydrocarbons with 5 carbons, you can imagine a number of ways of putting the carbon backbone together

CH3-CH2-CH2-CH2-CH3

C – C – C

All of these compounds have a molecular formula of C5H12 are referred to as structural isomers. All are known compounds

Structural isomers have similar but different properties and can be distinguished from one another by identifying carbon atoms that have different number of carbon atoms attached

CH

CH3

CH2

CH3CH3

CH2CH3

HC CH3

CH3

Are these structural isomers?

These are two different ways of drawing the same compound

butane

Some different ways of writing butane; all of then refer to the same compound because of rotation about the carbon-carbon bonds

A systematic way of naming alkanes and identifying identical structures

1. Locate the longest carbon chain in the molecule: this identifies the parent alkane

the longest carbon chain is 4: butane C

CH3

CH2

CH3CH3

CH2CH3

C CH3

CH3

CH3

CH32. Identify the points of branching and count the number of carbons in each branch

2 points of branching at the same carbon: each 1 carbon

3. Name the branch on the basis of the number of carbons by dropping the ane of the parent and adding yl:

4. Give the first branch encountered the lowest number and use the prefix di, tri, tetra, ... for multiple groups

2 methyl groups both at carbon 2

2,2-dimethylbutane

methane methyl

Name the following:parent:groupsposition of groups

hexaneboth methyl

2 at carbons 2 and 4

2,4-dimethylhexane

parent:groupsposition of groups

heptane2 chlorines and methyl

chlorine at positions 3 and 5, methyl at position 3

3,5-dichloro-3 methylheptaneCl as a group is named chloro

Name this compound:

longest carbon chain

groups:

5, pentane

chloro, methyl

location: CH3 at C2 and Cl at C3

3-chloro-2-methylpentane

CH3-CH2-CH2-CH2-CH2-CH2-CH-CH2-CH2-CH3

│ CH2CH3

longest carbon chaingroups:

10, decaneethyl

location: ethyl at C4

4-ethyldecane

What is a general molecular formula for these alkanes?

if n = the number of carbon atoms, note that the number of hydrogens is? 2n+2

The general formula for all the compounds is given by CnH2n+2

How many C?

How many H?

8

18

2*8+2 = 18

Can we make an alkane with n C but less the 2n+2 hydrogens?

C3H6 C4H8

C5H10C6H12

cycloalkanes can have less the (2n+2) H’s

H-CH2CH2CH2CH2-H .

The textbook often draws hydrocarbons without all of the hydrogen shown. This is an abbreviated way of drawing the molecule. Please remember that carbon always has 4 bonds to it and if all the bonds are not designated, you need to assume there are hydrogens at these positions

H2C

H2CCH2

CH

CH2

CH

CH2-CH3

Cl

parent: cyclohexane

groups: ethyl, chloro

location: 1, 3

1-chloro-3-ethylcyclohexane

1-ethyl-3-chlorocylohexane

CHCH3 CH3

parent: groups:

cyclopentaneisopropyl

isopropylcyclopentane

Properties of n-alkanes

The properties of alkanes include beingnonpolarinsoluble in waterless dense than waterflammable in air

Alkanes with 1–4 carbon atoms aremethane, ethane, propane, and butaneall are gases at room temperatureall are used as heating fuels

Alkanes with 5–8 carbon atoms are liquids at room temperatureall are very volatileall are found in gasoline

Alkanes with 9–17 carbon atoms are liquids at room temperatureall have higher boiling pointsall are found in kerosene, diesel, and jet fuels

Alkanes with 18 or more carbon atomsare waxy solids at room temperatureare used in waxy coatings of fruits and vegetables

The hydrocarbons in crude oil are often cracked to produce smaller hydrocarbons which are separated by their different boiling points

All hydrocarbons can be burned in oxygen to produce carbon dioxide and water

C8H18 + O2 = CO2 + H2O + Heat

C8H18 + O2 = 8CO2 + 9H2O + Heat

C8H18 + 25/2O2 = 8CO2 + 9H2O + Heat

2C8H18 + 25O2 = 16CO2 +18H2O + Heat

Compounds of carbon with other elements Oxygen oxygen has 6 valence electrons; needs to form 2 bonds

If a molecule contains a hydroxyl (–OH) group, it is called an alcohol.

The the oxygen atom is bonded to two carbon atoms it is called an ether (–C–O–C–) .

O

O

ethyl alcohol, ethanol hydroxyethane

In both these cases, the oxygen is single bonded to carbon

..

Compounds of carbon with other elements Nitrogen nitrogen has 5 valence electrons; needs to form 3 bonds

NIn an amine, nitrogen is attached by a single bond to 1, 2, or 3 different carbon atoms

..

2 carbons

A Summary of the typical functional groups encountered in organic chemistry

Functional groupsare a characteristic feature of organic molecules that behave in a predictable way are composed of an atom or group of atomsare groups that replace a H in the corresponding alkaneprovide a way to classify families of organic compounds