1. Hydrocarbon Isomerism & Bond Reactivity

2. Introduction
Every organic molecule has a skeletal framework of C and H
Octane has 8 C atoms with C – C bonds to make a linear Chain
Each C is also bonded to a number of H atoms to fulfill its octet
Octane is an example of a hydrocarbon because it only has C and H

3. Functional Groups
The unique properties of an organic compound depend on the carbon skeleton and the presence of any functional groups
A functional group is a set of atoms that are bound in a characteristic pattern and exhibit predictable chemical behavior
The simplest functional groups involve >C=C< and –C≡C – in a skeletal framework
As long these molecules only contain C and H atoms these are still hydrocarbons

4. Hydrocarbon Classes
3-hexyne
hexane
Alkanes are hydrocarbons that contain only single bonds
Alkenes are hydrocarbons that contain one or more >C=C<
Alkynes are hydrocarbons that contain one or more –C≡C –
Aromatics are hydrocarbons that contain one or more
benzene
3-hexene

5. A molecule’s “backbone” is not always linear
Often there are many ways to build a framework that corresponds to the molecular formula
Compounds that share the same formula but have a different structure are called isomers

6. Naming Alkanes
All alkanes are named according to the parent name of the longest continuous carbon chain in the molecule
Names of the straight-chain alkanes with skeletons of 1-10 Carbons

7. Simplifying the Structures
There are different ways to draw molecular structures
Up till now we have drawn the extended structure

8. Substituents
Any C groups attached to the main chain are called substituents
To name an alkane find the longest continuous carbon chain and its name
Number the C in the chain starting from the side closest to the substituents
Identify the substituents and name them (if CH3- methyl, if CH3CH2- ethyl …. Cl- chloro, Br- bromo ) and place the number of the C in the chain they are attached to in front of the name followed by a dash
If there are more than one substituent of the same type group them (2 methyl groups are called dimethyl, 3 methyl groups trimethyl etc)
Combine the substituent identifiers with the parent name

9. Physical Properties All hydrocarbons exhibit similar properties
Alkane
Boiling Point
Alkene
Aromatic
Pentane
35oC
2-pentene
36oC
Hexane
68oC
1-hexane
66oC
Cyclohexane
80oC
Cyclohexene
85oC
Benzene
Heptane
98oC
1-heptane
94oC
Toluene
111oC
2-methylheptane
118oC
Cycloheptene
115oC
Ethylbenzene
136oC
Ethylcyclohexane
132oC
4-vinyl-cyclohexane
130oC
Physical Properties
All hydrocarbons exhibit similar properties
All are non-polar and less dense than water
All are immiscible in water (don’t mix)
They do have differing boiling points though

10. Chemical Properties reaction with Br2
Alkane
Alkene
Add
alkane or alkene
Chemical properties differ
Alkenes and alkynes react quickly with bromine (Br2) to produce the dibromoalkane
Alkanes react slowly with bromine (Br2) to produce the bromoalkene (in light)
Aromatics do not react with bromine except if you add AlCl3
AlCl3

11. Chemical Properties reaction with KMnO4
Alkane or aromatic (negative test)
Alkene (positive test)
Alkenes react quickly with potassium permanganate (KMnO4) to produce the diols
Alkanes and Aromatics do not react with KMnO4
Alkenes therefore turn the solution from purple to a light brown/yellow

12. Part A Make a model of the 3 isomers of pentane and name them
Make a model of chloroethane and draw the 3d structure for it and ethane
Make a model of 1,2 dichloroethane and draw the 3d structure
Make a model of ethene C2H4
Make a model chloroethane and 1,2 dichloroethane
Answer questions 1-3 on the data sheet
Part A

13. B: Boiling Point Determination
Instructions
Vapor
water
methanol
Boiling chip
Assemble apparatus shown
¾ fill 250 ml beaker with tap water
Turn on hotplate
Add boiling chip in test tube and 3 mL methanol
Cap test tube with split stopper insert thermometer so its tip is 2 cm above the hexane
When water is boiling turn off the hotplate
Lower clamp with test tube until methanol just below surface of water
When hexane boils and is steadily dripping off tip of thermometer record T
Repeat for a mystery hydrocarbon liquid
Identify your liquid based on the BP
Part B
Calcium caseinate has its isoelectric (neutrality) point at pH 4.6. Therefore, it is insoluble in solutions of pH less than 4.6. The pH of milk is about 6.6; therefore casein has a negative charge at this pH and is solubilized as a salt. If acid is added to milk, the negative charges on the outer surface of the micelle are neutralized (the phosphate groups are protonated) and the neutral protein precipitates:
Ca2+Caseinate + 2HCl Casein + CaCl2
B: Boiling Point Determination

14. 3 drops 1% bromine solution
hexane
cyclohexane
toluene
unknown
Part C
If the red-brown color persists, add 2 crystals of AlCl3 and record changes
For any test tube where the red-brown color continues to persist hold the sample in front of a bright light for 3 minutes, and record your observations

15. Part C 2 drops 1% KMnO4 solution 10 drops hexane cyclohexane toluene
unknown
Part C
Stopper the test tubes and shake for 10 s
Then allow them to stand for 2 minutes
Record the color after 2 mins
Remember that if the color stays purple it didn’t react

16. Part D Identification of the Mystery Substance
The mystery hydrocarbon is one of those listed below
Using your results from parts B and C propose an identity for your mystery hydrocarbon and record it on the data sheet on page 146
Alkane
Boiling Point
Alkene
Aromatic
Pentane
35oC
2-pentene
36oC
Hexane
68oC
1-hexane
66oC
Cyclohexane
80oC
Cyclohexene
85oC
Benzene
Heptane
98oC
1-heptane
94oC
Toluene
111oC
2-methylheptane
118oC
Cycloheptene
115oC
Ethylbenzene
136oC
Ethylcyclohexane
132oC
4-vinyl-cyclohexane
130oC