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
Oil and 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 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 CH can be distinguished from one another by identifying carbon CH3 3 atoms that have different number of carbon atoms attached CH CH2 CH3 Are these structural isomers?
CH3 CH2 These are two different ways of drawing HC CH the same compound 3 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
CH CH3 the longest carbon chain is 4: butane 3 C CH2
CH3 2. Identify the points of branching and count the number of carbons CH3 in each branch
2 points of branching at the same carbon: each 1 carbon CH3 CH2
CH3 C CH3 3. Name the branch on the basis of the number of carbons by dropping CH3 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: hexane groups both methyl 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:
longest carbon chain 5, pentane groups: 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 chain 10, decane 4-ethyldecane groups: ethyl
location: ethyl at C4 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? 8 How many H? 18
2*8+2 = 18 . 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 C4H8
C5H10 C6H12 CH2-CH3 parent: cyclohexane
CH groups: ethyl, chloro ≡ H2C CH2 location: 1, 3 H2C CH CH2 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 CH3 CH parent: cyclopentane groups: 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
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O If a molecule contains a hydroxyl (–OH) group, it is called an alcohol.
ethyl alcohol, ethanol hydroxyethane O 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 Compounds of carbon with other elements Nitrogen nitrogen has 5 valence electrons; needs to form 3 bonds
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N In 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 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