1. Introduction Alkanes Nomenclature
Organic Chemistry
Introduction
Alkanes
Nomenclature

2. Electron Dot structuresB C N O F Li Be
Class exercise 1:
Draw the electron dot structure of Carbon
Class exercise 2:
Draw the electron dot structure of oxygen and fluorine Ne

3. Lewis Dot structures B C N O F Li Be
Along with carbon, we will also deal with hydrogen, oxygen, nitrogen and the halogens (fluorine, chlorine, bromine and iodine). Let's go through some of the bonding features of each of these elements also. (The properties listed below are summarized in a table at the bottom of the page.)
Again let's start with carbon. Carbon has four unpaired electrons in its outer shell. It needs four electrons to get eight in its outer shell; therefore, it tends to form four covalent bonds. It can form these four covalent bonds to other carbon atoms or to atoms of other elements such as hydrogen, oxygen, nitrogen, or chlorine or a wide variety of others as well. Because it can form four bonds, carbon is said to have a valence of four. It can form single, double or triple bonds.
Hydrogen is quite different. It has one electron in its outer shell and needs only one more to complete its outer shell. So it can form one covalent bond, and it is said to have a valence of one. It can form only single bonds.
Oxygen has six electrons in its outer shell, needs two more, and will form two covalent bonds to get those two additional electrons. Thus, oxygen is said to have a valence of two. Please note the difference between "valence" and "valence electrons". Oxygen has a valence of two, and it has six valence electrons. It can form single or double bonds.
Nitrogen has five valence electrons, five electrons in its outer shell, and needs three electrons to complete that outer shell. It can gain those three through covalent bonds by forming three covalent bonds. So, it is considered to have a valence of three. It can form single, double or triple bonds.
Chlorine is typical of the halogens so I will use it as a specific example of the halogens in general. Everything I say about the bonding of chlorine can be applied to the other halogens as well. Chlorine has seven valence electrons, needs one to fill its outer shell, so chlorine has a valence of one and can form only single bonds.

4. Organic Chemistry Chemistry of Carbon Bonding of H,O, X and N
"Carbon is element number 6, which means that it has six protons in its nucleus and a total of six electrons. Two of those electrons are in the first shell and the remaining four electrons are valence electrons which are found in the outermost shell of carbon. Carbon is a nonmetal, but it is not very electronegative, because it is not very far to the right side of the periodic table. Because it is a nonmetal, it likes to gain electrons in order to complete its outer shell. Because it is not very electronegative, it does not have the ability, in most cases, of completely gaining electrons to form negative ions. Consequently, it forms covalent bonds in which it shares its electrons with other elements. It can also bond to other atoms of carbon to form covalent bonds from one carbon to another. It is bonds of this type that give carbon its very central role in life."

5. Valence Summary C H O N Halogen Valence electrons 4 1 6 5 7 Valence 23
Bond types
Single
Double
triple
single

6. Complete Structural Formulas
Show the bonds between each of the atoms
H H
 
H  C  H H C H
CH4 , methane
First we have the molecular formula CH4. In the electron dot diagram you can see how the four valence electrons of carbon match up with the one valence electron of each of the four hydrogen atoms to give eight electrons around carbon. The electrons are arranged in four pairs representing four covalent bonds. You should remember that the arrangement of those four pairs of electrons is called a tetrahedral arrangement. The structural formula emphasizes the bonds rather than the electrons and shows one line for each of the bonds that connect the atoms together. Each line represents one shared pair of electrons. In methane, CH4 the four valence electrons of carbon are shared with the single electrons of four hydrogen (H) atoms. Each pair of electrons is a single bond, which can be drawn as a line. When a structure is drawn to show each bond, it is called a complete structural formula.

7. More Alkanes H H Condensed Structural Formulas H C C H CH3 CH3
H H Ethane
H H H
H C C C H CH3 CH2 CH3
H H H Propane
The complete structural formula for ethane shows the single bonds between two carbon atoms and six H atoms. The complete structural formula of propane shows the 3-carbon chain with single bonds to the attached H atoms. To write a condensed structural formula, the H atoms are written as a group next to their respective C atoms.

8. IUPAC Names Methane 1 CH4 Ethane 2 CH3CH3 Propane 3 CH3CH2CH3
Name # carbons Structural Formula
Methane 1 CH4
Ethane 2 CH3CH3
Propane 3 CH3CH2CH3
Butane 4 CH3CH2CH2CH3
Pentane 5 CH3CH2CH2CH2CH3
The names of organic compounds are determined by the IUPAC rules (International Union of Pure and Applied Chemistry). The stem of the name states the number of carbon atoms in the carbon chain of the compounds. The suffix, in this case –ane, indicates the alkane family.

9. IUPAC NAMES Hexane 6 CH3CH2CH2CH2CH2CH3
Name # carbons Structural Formula
Hexane CH3CH2CH2CH2CH2CH3
Heptane CH3CH2CH2CH2CH2CH2CH3
Octane CH3CH2CH2CH2CH2CH2CH2CH3
Nonane CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

10. Learning Check Alk1 A. What is the condensed formula for H H H H
H C C C C H
B. What is its molecular formula?
C. What is its name?

11. Solution Alk1
A. CH3CH2CH2CH3
B. C4H10
C. butane

12. So what exactly do these things do?
Properties of Alkanes
So what exactly do these things do?

13. Physical Properties of Alkanes
1. Combustion - Alkanes are inflammable, i.e. they burn.
2. Boiling and melting points
a. Both bp and mp increase with increasing carbon number for straight-chain
alkanes with formula CnH2n+2
Carbon Number Physical State
C1- C gases
C5 – C liquids
C17 – C30 oils and greases
C30 – C50 paraffin waxes
>C plastics (polyethylene)

14. b. Branching tends to lower the boiling point and raise the melting point
BP oC oC oC
MP oC oC oC
Explanation:
MP Branching reduces the flexibility of the molecule which reduces the entropy term
S in the equation Tmp = H/S. Since S is in the denominator, Tmp increases.
BP Branching reduces surface area (more compact structure), and therefore London
dispersion forces which control boiling point for these molecules.
3. Solubility – alkanes are nonpolar molecules and therefore insoluble in water, which
is polar. Alkanes are hydrophobic.
4. Densities – alkanes are less dense than water, with densities near 0.7 g/mL. Therefore
they float on water, e.g. Exxon Valdez oil spill.

15. Naming Hydrocarbons (nomenclature)

16. Drawing Structures: It’s All Good
2-butene
This is called the “condensed structure”
On a test, choose a method that shows all Hs
CH3CH=CHCH3
Using brackets can also shorten some formulas: CH3CH2CH2CH2CH2CH3 vs. CH3(CH2)4CH3

17. Basic Naming of Hydrocarbons
Hydrocarbon names are based on:
1)type,
2) # of carbons,
3) side chain type and position
1) name will end in -ane, -ene, or -yne
2) the number of carbons is given by a “prefix”
1 meth eth prop but-
5 pent hex hept oct-
9 non dec-

18. Basic Naming of Hydrocarbons
Q - What names would be given to these:
7C, 9C alkane
2C, 4C alkyne
6C, 3C alkene
heptane, nonane
ethyne, butyne
Hexene, propene

19. Mnemonic for First Four Prefixes
Monkeys
Eat
Peeled
Bananas
First four prefixes
Meth-
Eth-
Prop-
But-

20. ? Decade Decimal Decathalon Other Prefixes Pent- Oct- Dec-
Hex-, Hept-, Non-

21. Straight chain hydrocarbons Learning Check
Pentane
Propane
Heptane
Ethane
Octane

22. Numbering Carbons 1-pentene Q- draw pentene
A- Where’s the double bond? We # C atoms.
Naming compounds with multiple bonds is more complex than previously indicated.
When 2+ possibilities exist, #s are needed.
Always give double bond the lowest number.
Q - Name these
C2H4
2-butene
ethene
3-nonyne

23. Learning Check - Numbering Carbons
Name the following compounds:
C2H4
2-butene
ethene
3-nonyne

24. The names of molecules with branches are based on: side chains, root
Naming Side Chains C H 3
The names of molecules with branches are based on: side chains, root
2,3-dimethylpentane
The “root” or “parent chain” is usually the longest possible hydrocarbon chain.
The root must include multiple bonds if they are present. If a cyclic structure is present it will be the root even if it is not the longest chain.
Side chains are also called “side branches” or “alkyl groups”. Their names end in -yl.
Common side chains :
-CH3 methyl, -CH2CH3 ethyl, -CH2CH2CH3 propyl

25. IUPAC Rules for Naming Hydrocarbons
Choose the correct ending: -ane, -ene, or -yne
Determine the longest carbon chain. Where a double or triple bond is present, choose the longest chain that includes this bond. If there is a cyclic structure present, the longest chain starts and stops within the cyclic structure.
Assign numbers to each C of the parent chain. For alkenes and alkynes the first carbon of the multiple bond should have the smallest number. For alkanes the first branch (or first point of difference) should have the lowest #. Carbons in a multiple bond must be numbered consecutively.
Attach a prefix that corresponds to the number of carbons in the parent chain. Add cyclo- to the prefix if it is a cyclic structure.

26. IUPAC Rules for Naming Hydrocarbons
Determine the correct name for each branch (“alkyl” groups include methyl, ethyl, propyl, etc.)
Attach the name of the branches alphabetically, along with their carbon position, to the front of the parent chain name. Separate numbers from letters with hyphens (e.g. 4-ethyl-2-methyldecane)
When two or more branches are identical, use prefixes (di-, tri-, etc.) (e.g. 2,4-dimethylhexane). Numbers are separated with commas. Prefixes are ignored when determining alphabetical order. (e.g. 2,3,5-trimethyl-4-propylheptane)
When identical groups are on the same carbon, repeat the number of this carbon in the name. (e.g. 2,2-dimethylhexane)

27. Example: use the rules on this handout to name the following structure
Naming Side Chains
Example: use the rules on this handout to name the following structure
Rule 1: choose the correct ending
ene

28. Naming Side Chains
Rule 2: determine the longest carbon chain
ene

29. Naming Side Chains
Rule 3: Assign numbers to each carbon
ene

30. Naming Side Chains
Rule 3: Assign numbers to each carbon
ene

31. Naming Side Chains Rule 4: attach prefix (according to # of Cs) ene
1-hexene

32. Naming Side Chains Rule 5: Determine name for side chains 1-hexene
ethyl
methyl
methyl
Rule 5: Determine name for side chains
1-hexene
1-hexene

33. Naming Side Chains 2-ethyl-4-methyl-4-methyl-1-hexene 1-hexene ethyl
Rule 6: attach name of branches alphabetically
2-ethyl-4-methyl-4-methyl-1-hexene
1-hexene

34. Naming Side Chains Rule 7,8: group similar branches
ethyl
methyl
methyl
Rule 7,8: group similar branches
2-ethyl-4-methyl-4-methyl-1-hexene
1-hexene

35. Similar questions will be issued on Moodle and in the tutorial sheets
Naming Side Chains
ethyl
methyl
methyl
Rule 7,8: group similar branches
2-ethyl-4,4-dimethyl-1-hexene
Similar questions will be issued on Moodle and in the tutorial sheets

36. Learning Check – Naming
propene
2-butene
2,4-dimethyl-2-pentene
1-butyne

37. a) 3,3-dimethyl-1-pentene b) sameC H C H 3 3 C H C C C H C H C H 3 2 C H C H 2 3
c) 5-ethyl-4-methyl-2-heptyne