11-Introduction to Organic Chemistry 

• Organic chemistry is the study of the millions of covalent compounds of the element carbon
• These structurally diverse compounds vary from naturally occurring petroleum fuels to DNA and the molecules in living systems.
• Organic compounds also demonstrate human ingenuity in the vast range of synthetic materials created by chemists. - Many of these compounds are used as drugs, medicines and plastics.

==Why can carbon form rings and very long chains?==

• A carbon atom has 4 electrons in its outer shell, so it forms 4 covalent bonds
• ==Carbon-carbon bonds== are relatively ==strong and non-polar==

Displayed formula

• shows every atom and every bond in the molecule
• shows the arrangement of atoms showing all the bonds and atoms in the molecule

Structural formula

• shows the unique arrangement of atoms in a molecule in a simplified form, without showing all the bonds

Skeletal formula

• carbon atoms are not drawn at all
• straight lines represent carbon to carbon bonds
• carbon atoms are assumed to be where the bonds meet
• shows that bonds of the carbon skeleton only.
• Hydrogen and carbon atoms are not shown, only functional groups are

Free radicals

• when a covalent bond breaks in a way that one electron goes to each atom that originally formed the bond
• the fragments of the original molecule have an unpaired electron - free radicals
• extremely reactive

@@Nomenclature - naming organic compounds@@

• The system used for naming compounds was developed by IUPAC
• Systematic names tell us… about the structure of the compounds rather than just the formula

Roots

• tells us whether there are any double bonds
• -@@ane@@ means no double bond
• -@@ene@@ means double bond

Functional groups

• reactive groups attached to a hydrocarbon chain
• halogenalkenes are named using a prefix rather than a suffix (bromo-, chloro-, fluoro-)

@@Chain and position isomers @@

• a number is used to tell us the position of any branching in a chain and the position of any functional group

• structural isomers have the same molecular formula but different structural formulae

@@Homologous series@@

• }}Homologous series is a family of organic compounds with the same functional group but different carbon chain length}}
• members of a homologous series have the same general formula
• successive members of the same homologous series increases by CH2
• 
• the length of the carbon chain $does not affect the chemical reactivity$ of the functional group
• the length of the carbon chain $does affect physical properties$ such as boiling and melting point
  • melting and boiling point increase by a small amount when the number of carbon in the chain increases
• $chain branching$ ==reduces== $the melting point$ because the $molecules pack together less well$

Isomers

• {{Isomers are molecules that have the same molecular formula but whose atoms are arranged differently{{
• There are 2 basic types of isomerism:
  • ==Structural isomerism==
  • ==Stereoisomerism==

Structural isomerism

• Structural isomerism - have the ==same molecular formula== but ==different structural formula==
• 3 Different Structural isomers:
  • $Positional isomerism$
  • $Functional group isomerism$
  • $Chain isomerism$

Positional isomerism

• the same functional groups attached to the main chain at different points
• same molecular formula but different position of the functional group

Functional isomerism

• functional groups that are different
• same molecular formula but different functional group

Chain isomerism

• a different arrangement of the hydrocarbon chain, e.g., branching

==Stereoisomerism==

• Stereoisomerism - where two or more compounds have the same structural formula. They differ in the arrangement of the atoms in space
• There are @@2 types of stereoisomerism:@@
  • ==E-Z isomerism==
  • ==Optical isomerism==

E-Z isomerism

• tells us about the position of substituents at either side of a carbon-carbon double bond
• two substituents can either be in the @@same side of the bond (Z isomer)@@ or on %%opposite sides (E isomer)%%
• substituted groups joined by a single bond can rotate around the single bond
• there is no rotation around a double bond
• have @@different chemical and physical properties@@
• e.g. different reaction rates for the same reaction (chemical property) or different melting/boiling points (physical property)
• \
• 

How can I tell if the compound is stereo or structural?

• Is there is @@no restricted bond rotation around C-C bond, (no double bond)@@ so it is @@structural isomerism@@
• structural isomerism = no restricted bond rotation = no double bond
• stereo isomerism = a restricted bond rotation = double bond

How to deduce isomers?

• Step 1: Draw the structural formula of the compound

• Step 2: Determine whether it is a stereo or structural isomer
  • There is no restricted bond rotation around the C-C bond, so it is structural isomerism
• Step 3: Determine whether it is a functional group, chain or positional isomerism
  • ==Functional group?== No, as there are no functional groups
  • ==Positional?== No, as there are no functional groups which can be positioned on different carbon atoms
  • ==Chain?== Yes!

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How to deduce isomers? Example 2

• Step 1: Draw the possible structural formula of the compound

• Step 2: Determine whether it is a stereo or structural isomer

The compound has to be ==unsaturated== for it to have molecular formula C2H2Cl2 ; Due to the ==double bond== there is ==restricted rotation about the C-C bond;== This compound will therefore display ==geometrical isomerism==