Chapter 11

Organic Chemistry

The study of the compounds of carbon

Some Properties Typical of Organic Compounds Organic compounds form covalent bonds have low melting points and boiling points tend to be flammable are soluble in non-polar solvents are not very soluble in water

A 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

Oil and water

The bonding environment of carbon: Type of bonds

Geometry of carbon

4 single bonds

tetrahedral geometry

2 single bonds + 1 double bond

triangular at carbon

1 single bond + 1 triple bond

linear at carbon

2 double bonds

linear at carbon

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 carboncarbon 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

CH3

CH3

CH CH2 CH3

Are these structural isomers? These are two different ways of drawing the same compound

CH3

CH2 HC CH3

CH3

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:

CH3

CH3

butane

C

2. 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

CH3

CH2 CH3

CH3

CH2

CH3

C

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

CH3

CH3

Name the following:

hexane parent: both methyl groups position of groups 2 at carbons 2 and 4 2,4-dimethylhexane

parent: heptane groups 2 chlorines and methyl position of groups chlorine at positions 3 and 5, methyl at position 3 Cl as a group is named chloro

3,5-dichloro-3 methylheptane

Name this compound:

5, pentane

longest carbon chain

chloro, methyl

groups: 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 chain groups:

10, decane ethyl

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? The general formula for all the compounds is given by CnH2n+2 How many C?

8

How many H?

18 2*8+2 = 18

2n+2

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

. H-CH2CH2CH2CH2-H

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

C3H6 C5H10

C6H12

C4H8

≡

CH2-CH3

parent: cyclohexane

CH

groups: ethyl, chloro

H2C

CH2

H2C

CH CH2

location: 1, 3 Cl

1-chloro-3-ethylcyclohexane 1-ethyl-3-chlorocylohexane

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

CH3

CH

CH3

parent: groups:

cyclopentane isopropyl

isopropylcyclopentane

Properties of n-alkanes The properties of alkanes include being nonpolar insoluble in water less dense than water flammable in air Alkanes with 1–4 carbon atoms are methane, ethane, propane, and butane all are gases at room temperature all are used as heating fuels Alkanes with 5–8 carbon atoms are liquids at room temperature all are very volatile all are found in gasoline Alkanes with 9–17 carbon atoms are liquids at room temperature all have higher boiling points all are found in kerosene, diesel, and jet fuels Alkanes with 18 or more carbon atoms are waxy solids at room temperature are 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

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

ethyl alcohol, ethanol hydroxyethane The the oxygen atom is bonded to two carbon atoms it is called an ether (–C–O–C–) . In both these cases, the oxygen is single bonded to carbon

O

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

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

2 carbons

N

A Summary of the typical functional groups encountered in organic chemistry

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