1. Organic Chemistry

2. Introduction
Organic chemistry is the study of carbon compounds, and specifically compounds containing a C−H bond.
There are more compounds of carbon than all of the other elements put together
This is because of the fact that carbon atoms can join together to form chains and rings; a property called catenation
The source of many carbon compounds is crude oil; many substances can be separated from this complex mixture by fractional distillation

3. Hydrocarbons
Hydrocarbons are the foundation molecules of organic chemistry
Hydrocarbons can be separated into two main groups:
Aliphatic compounds
Aromatic compounds
There are different methods for writing and drawing the structures of hydrocarbons, which will be discussed later

4. Aliphatic Compounds
Aliphatic compounds are divided into alkanes, alkenes and alkynes

5. Saturated or unsaturated
Alkanes
Alkanes are referred to as saturated hydrocarbons; meaning that they contain only single carbon-carbon bonds.
In other words, they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms present
General formula: CnH2n+2
# of carbon atoms
# of hydrogen atoms
Saturated or unsaturated 4 10
Saturated 5 12 6 13
Unsaturated

6. The carbons in all alkanes can be assumed to be sp3 hybridised with a tetrahedral shape

7. Structural isomers
As the number of carbons atoms in alkanes increases beyond 3, the number of structural isomers increases rapidly
Heptane (C7H16) has 9 structural isomers
n stands for normal
n-butane

8. Structural Formulas
C7H16 is not a structural formula as it could be any of the isomers.
Condensed formulas are therefore used:
CH3(CH2)5CH3 2 4 6 1
Skeletal formula
Only the carbons are drawn 3 5 7

9. The first 10 straight-chain Alkanes
Name
Molecular Formula
Number of isomers
Melting Point (°C)
Boiling Point (°C)
Methane
CH4
−182.5
−161.6
Ethane
CH3 − CH3
−183.3
−88.6
Propane
CH3− CH2− CH3
−189.7
−42.1
Butane
CH3− (CH2)2 − CH3 2
−138.3
−0.5
Pentane
CH3− (CH2)3 − CH3 3
−129.8
36.1
Hexane
CH3− (CH2)4 − CH3 5
−95.3
68.7
Heptane
CH3− (CH2)5 − CH3 9
−90.6
98.4
Octane
CH3− (CH2)6 − CH3 18
−56.8
125.7
Nonane
CH3− (CH2)7 − CH3 35
−53.5
150.8
Decane
CH3− (CH2)8 − CH3 75
−29.7
174.0

10. Nomenclature
All organic compounds are named based on the recommendations of the International Union of Applied Chemistry (IUPAC).
The rules are as follows:
The parent name of the hydrocarbon is based on the longest continuous chain of carbon atoms in the molecule
Heptane

11. An alkane less one hydrogen is an alkyl group, e. g
An alkane less one hydrogen is an alkyl group, e.g. methane with one less hydrogen (CH3) is a methyl group
Methane less 1 hydrogen = Methyl
Ethane less 1 hydrogen = Ethyl

12. When one or more hydrogen atoms are replaced by other groups, the name must include the position where replacements are made. The procedure is to number each carbon of the longest chain in the direction that gives the smallest number for the locations of all branches. 1 7 5 6 7 3 2 1

13. When there is more than 1 alkyl branch of the same kind present, we use a prefix such as di-, tri-, or tetra- with the name of the alkyl group.
When there are two or more different groups they are listed alphabetically
Longest continuous chain = Replacement groups =
Pentane
Methyl
2,3-dimethylpentane
3-ethyl, 2-methylpentane

14. 4-ethyl-2-methylheptane1
7 carbons = heptane 5 6 7
4-ethyl-2-methylheptane

15. In the case that we have a substituent occurring at the same position regardless of which direction we number from we give priority to the substituent that occurs soonest alphabetically

17. Common substituent groups
Alkanes can have many different types of substituents.
Note that these groups are still listed alphabetically with the longest continuous carbon chain numbered in the direction that gives the lowest number(s)
Common substituent groups
Functional Group
Name
−NH2
Amino −F
Fluoro
−Cl
Chloro
−Br
Bromo −I
Iodo
−NO2
Nitro 3 2 1 4
1,2,3-tribromo,3-nitrobutane

18. Cycloalkanes
= CnH2n

19. Fluoro
ethyl 2 1 2 3 3 3 2 1 4 1 5 4 6
butyl 5 6
propyl

20. ‘Iso’ prefix
The prefix iso-, which stands for isomer, is commonly given to 2-methyl alkanes. In other words, if there is methyl group located on the second carbon of a carbon chain.
Isobutane (2-methylbutane)
Isopropane (2-methylpropane)

21. Properties of Alkanes
Non-polar molecules due to very similar electronegativities
Immiscible with water (not soluble)
Dispersion forces increase as the number of carbons increases
Low density; most are less dense than water
Boiling point increases as the number of carbon chains increases in the molecule
Generally have low chemical reactivity
Excellent fuels; highly exothermic combustion reactions

22. Alkenes
Unsaturated hydrocarbons containing at least one carbon-carbon double bond
Alkenes have the general formula CnH2n
The carbon atoms that form the double bonds are sp2 hybridized

23. The double bond consists of 1 sigma bond and 1 pi bond (for each carbon atom)
The hybridised sp2 orbitals form sigma bonds (σ).
The remaining hybridised 2p orbitals form pi bonds (π)
Ethylene (C2H4)

24. Structural Isomers of alkenes
Changes in the position of the double bond or in the positions of their substituents

25. Geometric Isomers of alkenes
Each carbon is bonded to 2 different groups
Geometric Isomers of alkenes
Occur due to the restriction to rotation about the C = C bond (the double bond is rigid).
Geometric isomers exhibit differences in both physical and chemical properties, but have the same molecular formula and structure.
The substituent groups are on the same side
The substituent groups are on different sides

27. Priority is assigned according to atomic mass
Cis and Trans does work well beyond di-substituted alkenes. In this case E/Z are used to prioritise substituents Cl F
Priority is assigned according to atomic mass Br H

29. Entgegen-Zusammen Nomenclature
Trans
Cis
Entgegen-Zusammen Nomenclature
Methyl 1 2 2 3 3 5 4 5 4 1
Longer chain takes precedence
(E)-3-methyl-2-pentene
(Z)-3-methyl-2-pentene
All cis- molecules are Z, but not all Z molecules are cis-; all trans-molecules are E, but not all E molecules are trans

30. Assign E or Z to each molecule1 3 5 7 4 6 2

32. Cis Isomer Trans Isomer Reason
More Polar
Less Polar
In trans-isomers the charge is balanced on opposite sides of the double bond
Higher boiling point
Lower boiling point
Intermolecular forces; stronger for cis-isomers
Lower melting point
Higher melting point
Trans isomers ‘pack together’ to form a lattice better due to their shape
Higher solubility in inert solvents
Lower solubility in inert solvents
Intermolecular forces
In acyclic systems the cis isomers are more unstable than trans isomers
In acyclic systems the trans isomers are more stable than cis isomers
Having both substituent groups on the same side of a double bond can produce steric hindrance
Steric hindrance is basically some bulky groups prevent other groups from attacking at a certain site

33. Alkynes
Unsaturated hydrocarbons containing at least one carbon-carbon triple bond
Alkenes have the general formula CnH2n−2
The carbon atoms that form the triple bond are sp hybridized

35. Alkyne Isomers
Alkynes have structural isomers but no geometrical isomers
Changes in the position of the triple bond or in the positions of their substituents
CH3 − CH2 − CH2 − CH2 − C ≡ CH
CH3 − CH2 − CH2 − C ≡ C − CH3

36. Naming Alkenes and Alkynes
IUPAC Rules
Identify the longest continuous chain of carbon atoms that contains the double/triple bond. (The chain must contain the double/triple bond, even though it may not be the longest chain)
Number the main chain beginning at the end that will result in the lowest possible number for the double or triple bond. Add the number as a prefix.
The suffix of the compound is “-ene” for an alkene or “-yne” for an alkyne

37. 1) 2)

38. Add substituents as prefixes, with their positions, in alphabetical order.

39.
4-ethyl-7-methyl-5-decyne

40. 4,4-diflouro-1,2,5-heptatriene
2,4-dichloro-1-pentene
1,5-hexadiene
4,4-diflouro-1,2,5-heptatriene

41. 3-methyl-cyclopentene
If there is only 1 double bond in a ring structure you do not need to add the position of the double bond to the name (it is always 1) 4 6 5 5 1 3 4 2 6 2 3 1
3-methyl-cyclopentene
2,3,5 not 1,4,6

42. Assign numbers so that the double bond has the lowest possible number
A molecule that contains both double and triple bonds is called an alkenyne
Assign numbers so that the double bond has the lowest possible number 2 4 1 5 3
1,3-Pentenyne
1-Penten-3-yne 6 7 8 9
5-ethyl-2-methyl-2,7-nonenyne

44. Aromatic Hydrocarbons
Aromatic hydrocarbons can be defined as cyclic hydrocarbons with delocalised pi electrons between carbon atoms of ring.
Since benzene is simplest aromatic compound, aromatic hydrocarbons can be defined as hydrocarbons which contain one or more benzene rings.

45. Aromatic Nomenclature
Straightforward for monosubstituted benzenes

47. Disubstituted Benzenes
1,3-dibromobenzene
1,4-dibromobenzene
1,2-dibromobenzene
p-dibromobenzene
para
o-dibromobenzene
ortho
m-dibromobenzene
meta

48. Compounds in which the two substituted groups are different are named accordingly:4 5 3 3 3 2 2 2 1 1 1
3-ethyl-5-methylchlorobenzene

49. For di-substitutions numbers or m, o, p can be used

50. Xylene
Toluene
m- o- p-

51. Functional Groups
Functional groups are structural units within organic compounds that are defined by specific bonding arrangements between specific atoms.
It is important to be able to quickly recognize the most common functional groups, because they are the key structural elements that define how organic molecules react.

52. Alcohols and Phenols
Alcohols contain the hydroxyl function group (─OH)
Alcohols can be identified as primary, secondary or tertiary based on their structures
Primary – the carbon which carries the hydroxyl group is only bonded to one alkyl group
Secondary - the carbon which carries the hydroxyl group is directly bonded to two alkyl groups, which may be the same or different.
Tertiary - the carbon which carries the hydroxyl group is bonded directly to three alkyl groups, which may be any combination of same or different.

55. Naming Alcohols
1. Find the longest chain containing the hydroxy group (OH). 2. Place the OH on the lowest possible number for the chain. With the exception of carbonyl groups, such as ketones and aldehydes, the alcohol or hydroxy groups have first priority for naming. 3. When naming a cyclic structure, the -OH is assumed to be on the first carbon unless the carbonyl group is present, in which case the later will get priority at the first carbon. 4. When multiple -OH groups are on the cyclic structure, number the carbons on which the -OH groups reside. 5. Add the suffix -ol. When multiple alcohols are present use di, tri, etc before the ol, after the parent name. ex. 2,3-hexandiol. If a carbonyl group is present, the -OH group is named with the prefix "hydroxy," with the carbonyl group attached to the parent chain