Upload
lytuyen
View
220
Download
2
Embed Size (px)
Citation preview
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
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 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: 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
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:
location:
10, decaneethyl
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 CH3parent: 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